Investigation of flame emission and absorption ...
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Master of Science Thesis by Susan Lindecrantz Division of Combustion Physics Lund University
May 2010
Investigation of flame emission and absorption spectroscopy using the HITRAN/HITEMP database and simulations for concentration and temperature determination in combustion environments
2 Abstract
Susan Lindecrantz | LTH
© Lindecrantz, Susan
Investigation of flame emission and absorption spectroscopy using
the HITRAN/HITEMP database and simulations for concentration
and temperature determination in combustion environments.
Master of Science Thesis - May, 2010
Lund Report on Combustion Physics, LRCP-140
ISRN LUTFD2/TFC -- 140 -- SE
ISSN 1102-8718
Susan Lindecrantz
Division of Combustion Physics,
Department of Physics
Faculty of Engineering, LTH
Lund University
P.O. Box 118
S-221 00 Lund
Sweden
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Abstract
In this thesis the possibility of using the HITRAN/HITEMP database for
spectroscopic studies in combustion applications was investigated. The database was
used for radiative gas emission and absorption simulations. From the relation of the
radiative transfer for absorption (Beer-Lambert law) and emission, the spectra from
a methane/air premixed flame was measured and studied. A model for temperature
and species concentrations was suggested for combustion applications.
A Fourier Transform Infrared Spectrometer was used to record high resolution
spectra from specific height-positions around the visible flame zone, above a
premixed laminar burner. The recorded spectrum was used to study the flame
characteristics and compared with simulated emission spectra based on the
HITRAN/HITEMP database. The goal was to study the flame spectra and identify
its species and also to develop the simulation program.
The second application was to perform simulation just before combustion in a
spark assisted HCCI, i.e. homogeneous charge compression ignition, engine with a
spark-plug added in the combustion chamber. A simulation procedure was
formulated to be able to determine important parameters of the investigated gas
mixture, such as temperature and concentration. With this information the internal
exhaust gas recirculation (EGR) ratio just before combustion in the engine can be
determined with cycle-to-cycle resolution. For this investigation the concentration of
carbon dioxide was in focus to find the EGR with known temperature. An estimation
of the temperature would come from emission measurement on optically thick bands
originating from the in-cylinder gas just before combustion. An alternative method
to extract the temperature from two line absorption was investigated. With known
temperature the concentration can also be determined. A setup with an LED or a
diode laser was suggested for absorption measurements to find the concentration, in
which Beer-Lambert’s law is applied.
4 Content
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Content
Abstract ............................................................................................................................ 3
Content ............................................................................................................................. 4
Chapter 1 – Introduction ................................................................................................ 6
1.1 Objectives .................................................................................................................. 6
1.2 Scope .......................................................................................................................... 7
1.3 Outline ....................................................................................................................... 7
Chapter 2 – Background and Motivation ..................................................................... 8
2.1 The study of light and matter interaction .............................................................. 8
2.1.1 Atomic and molecular spectra ................................................................................ 8
2.1.2 Broadening of spectral lines ................................................................................. 10
2.2 The equation of radiative transfer ........................................................................ 11
2.2.1 Absorption ............................................................................................................ 12
2.2.2 Emission ............................................................................................................... 13
2.3 Line-by-line gas radiation simulation ................................................................... 14
2.3.1 HITRAN/HITEMP database ................................................................................ 14
2.3.2 Applications of HITRAN database ...................................................................... 15
2.4 Briefly about combustion ....................................................................................... 18
2.5 Internal combustion engine ................................................................................... 19
Chapter 3 - Experimental equipment and considerations ........................................ 21
3.1 Measurements with FTIR Spectrometer on a flame ........................................... 21
3.1.1 Experimental setup ............................................................................................... 21
3.1.2 Burner .................................................................................................................. 21
3.1.3 Slit ........................................................................................................................ 23
3.1.4 Fourier Transform Infrared Spectrometer .......................................................... 23
3.2 Engine experiment proposal .................................................................................. 25
3.2.1 Experimental setup ............................................................................................... 25
3.2.2 Possible light sources ........................................................................................... 26
3.2.3 Filters ................................................................................................................... 27
3.2.4 Engine .................................................................................................................. 28
3.2.5 Detectors .............................................................................................................. 29
Chapter 4 - Measurement and Simulations ................................................................ 31
4.1 Introduction ............................................................................................................ 31
4.2 Investigation and modelling infrared spectra in a flat flame ............................. 31
4.2.1 Experiment setup ................................................................................................. 31
4.2.2 Construction and simulation of flame spectra ..................................................... 32
4.2.3 Discussion of the flame investigation and simulation ......................................... 35
4.3 Temperature and Concentration simulations in the combustion chamber ...... 43
4.3.1 Implementation and simulation of engine spectra ............................................... 43
4.3.2 Suggestion of experiment setup ........................................................................... 48
4.3.3 Discussion of the engine simulations .................................................................. 49
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Chapter 5 – Conclusion and outlook ........................................................................... 60
5.1 Conclusion ............................................................................................................... 60
5.2 Outlook .................................................................................................................... 62
Acknowledgement ......................................................................................................... 64
Bibliography .................................................................................................................. 65
List of figures ................................................................................................................. 67
List of tables ................................................................................................................... 70
Appendix A: Code for flame investigation ................................................................. 71
A.1 CallProcessFTIRSpectra ........................................................................................ 71
A.2 CallOpticalDepthFunc ............................................................................................ 73
A.3 CallEmissionFunc .................................................................................................. 75
A.4 FlameEmissionSimulations .................................................................................... 78
Appendix B: Code for engine investigation ................................................................ 80
B.1 EngineOpticalDepthAndEmissionSimulations ...................................................... 80
B.2 EngineTemperatureSimulations ............................................................................. 82
B.3 EngineConcentrationSimulations ........................................................................... 85
B.4 CallTwoLineMethodAbsorptionTemperatureSimulation ...................................... 88
B.5 EngineConcentrationLEDSimulations ................................................................... 90
B.6 EngineConcentrationDiodeLaserSimulations ........................................................ 92
Appendix C: Comparison between measured and simulated spectra ..................... 94
C.1 Comparison for 3 mm below the flame zone ......................................................... 94
C.2 Comparison for 1 mm below the flame zone ......................................................... 94
C.3 Comparison at the flame zone ................................................................................ 95
C.4 Comparison for 1 mm above the flame zone ......................................................... 95
C.5 Comparison for 3 mm above the flame zone ......................................................... 96
Appendix D: Populärvetenskapling sammanfattning ............................................... 97
6 Chapter 1 – Introduction
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Chapter 1 – Introduction
1.1 Objectives
In today’s society, combustion is a large part of the everyday life; more than
90% of the energy used in the world is related to combustion [1]. The combustion of
fossil fuels leads to environmental problems, e.g. air pollutants and global warming,
requires a better understanding of the processes taking place in combustion.
Combustion also plays a big role in many industrial devices like engines and requires
industries to think about efficiency and environmentally friendly combustion to be
able to compete on an international market [2]. Many different non-intrusive optical
techniques for spectroscopic diagnostics have been developed for measurements of
species concentrations and temperatures.
Within the field of flame spectroscopic studies the infrared regions are of high
interest because important fuels like methane and combustion products like CO2, CO
and H2O are detectable in the infrared region. Detection of species, within the
infrared region, for concentration measurements can give an opportunity to better
understand the processes in an engine or a flame.
In previous master’s projects [3] it has been stated that spectroscopic
diagnostic techniques, e.g. LIF (Laser-Induced Fluorescence) and Rayleigh
scattering, are mostly conduced in the ultraviolet and visible region, in which
molecules undergo electronic transitions and thus have broad and structure less
distribution. Therefore the UV and visible regions are not always optimal for
spectroscopic diagnostics since these species do not have accessible transitions in
those regions. In the field of engine measurements, these methods require not only
optical access for observation and also an additional opening for introduction of
excitation signal to the combustion chamber.
However, in the infrared regions it can appear with strong rotational or
vibrational transitions, forming bands and band-heads. The spectra from a flame or a
combustion chamber may be recorded with line-of-sight absorption or thermal
emission spectroscopy. The main difficulties with diagnostics in this region are line
overlapping and spectral interference [3].
Combustion based engines will remain indispensable for many years, despite
efforts in introducing new energy sources; and thus urgently need to be improved
with regard to fuel efficiency and pollutant emission. One promising approach to
reduce pollution emission is to dilute the air with recirculated gases from the
preceding ignition cycle, so called internal exhaust gas recirculation (EGR). But, in
order to control and optimize this complicated process, new high-speed diagnostic
techniques are needed to determine the amount of recirculated gas in the engine,
especially near the spark plug, during intake and compression cycle by monitoring
water vapor or carbon dioxide. If one can, with line-of-sight measurements determine
the concentration of the carbon dioxide just before the ignition; it can be used to
estimate the amount of internal EGR.
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1.2 Scope
In this thesis the objective was to investigate the infrared radiation properties
from a flame or a gas flow theoretically with help of the HITRAN/HITEMP database
and compare with experimental measurements.
The main focus in this study was molecular species such as CO2, H2O, CO and
hydrocarbon fuels. The ambition was to be able to simulate or describe the detailed
spectroscopy of the infrared emission and absorption of hot gases mixtures. Based on
the simulations, valuable information likes temperature; species concentrations are to
be extracted from either emission or absorption spectroscopy.
A high resolution FTIR emission spectrum from laminar methane/air premixed
flame has been recorded, which will be used as a validation of the developed code for
hot gas emission simulation. A model for temperature and carbon dioxide
concentration measurement in an HCCI engine to obtain real time EGR ratio inform-
ation is going to be proposed.
1.3 Outline
The outline of the report is as follows: The following chapter contains a brief
review of the background theory applied in this work. A theory involving emission
and absorption is discussed as well as a brief description of combustion applications
such as premixed flames and the type of engine proposed for application of testing
the simulations. The concept of the HITRAN/HITEMP is described together with
line-to-line modelling used for simulations of the spectra. The following chapter
describes the experimental setup and its components used or suggested for the flame
and the engine part respectively. Thereafter, the creation and implementation of the
simulations is described, as are methods for the experiments. The result and the
objective of the project are presented together with the discussion, as well as
conclusions. In the appendix the written simulations programs and the spectra
obtained from the FTIR measurement and simulations are listed.
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Chapter 2 – Background and Motivation
The main physical phenomenon encountered in this work is infrared emission
and absorption spectroscopy, arising from the theory of radiative transfer and its
associated relation to optical depth. In the following sections, this theory has been
discussed. Important subjects such as line broadening effects, molecular and atomic
transitions have also been touched upon briefly. Afterwards constructions of the
different experiments and simulations are presented.
2.1 The study of light and matter interaction
In short, spectroscopy is the study of light and matter interaction and is used
important and useful in many various fields, e.g., astrophysics, lasers and
combustions studies; in which the different transition processes between various
energy states of the molecules are the atoms are studied. The aim of this work was to
extract valuable information from the studied system, such as species concentration
and temperature. For this purpose, different theories and models are used together
with experimentally determined energy levels and transition probabilities, found in
databases; to obtain a better understanding of the behavior of the system investigated
[4].
2.1.1 Atomic and molecular spectra
Matter consists of atoms and molecules, and the vast theory of matter will not
be discussed in detail in this work, for more information it is recommended to read
reference [4]. Simply put an atom contains a cloud of negatively charged electrons
surrounding a dense, positively charged nucleus containing protons and neutrons.
The electrons are attached to the nucleus of the atom by electromagnetic forces. A
transition in an atom between two levels gives rise to a single spectralline with finite
width. A molecule is a little more complicated than an atom, and contains a group of
atoms, held together by strong chemical bonds. The molecules can both vibrate and
rotate around a center axis, which also generates other types of transitions than the
usual electronic transitions. These transitions are called vibration and rotational
transitions, and form the so called ‘molecular bands’, a series of equally spaced lines
forming a band structure [4]. The spectra from molecular band from diatomic
molecules can be written as Eq. (2.1) with m = 1, 2, 3… = J+1, represent trans-
missions from the R-branch and m = -1, -2. -3, …, = -J for the P-branch.
2'''''')()( mBBmBBhvE vvvv −+++=∆ (2.1)
The constants B’v and B
’’v are rotational constant for the higher and the lower
rotational state respectively. This stems from the selection rules for the allowed
molecular transmissions of diatomic molecules. For anharmonic oscillator, the
vibrational quantum number changes with ∆vi = ±1, and the rotational quantum
number J only changes with one unit or none, ∆J = ±1 and 0. If a more complicated
model than the harmonic oscillator is used, the selection rules allows the following
vibrational transmissions: ∆vi = ±2, ±3… where the ∆vi = ±1, is called the
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fundamental and the ∆vi = ±2 is called the second harmonic and so on [5].
Combination or difference bands arise from anharmonic oscillators, when addition or
subtraction of two or more fundamental frequencies or overtones is allowed
respectively. Example of such bands are, vi+1+vi, 2vi+1+vi or vi+1-vi [6]. Sometimes
one can observe a so called ‘band head’ and it is at this point in which the branch
separation decreases to zero. This can be seen as an inversion of the branch. If B’v<
B’’
v then the band is shaded towards the red, for the other case the band is shaded
towards the violet [4].
Fig. 2.1 Illustrates the molecular energy structure, showing the electronic, vibrational and rotational
energy levels. The size of the energy difference between two electronic states is around a few eV,
two vibrational states a few 0.1 eV and two rotational states a few 0.001 eV.
Pure rotational lines are typically found in the microwave region, revibrational
lines in the infrared region, electronic transitions in the ultraviolet and visible range
of electromagnetic radiation. This division of the transitions comes from the
electronic and the molecular structures see Fig. 2.1 [7]. Light interactions between
two bound energy levels can occur through three possible radiative processes. The
atom or molecule can experience a spontaneous transition (also called emission)
given by the Einstein coefficient, A21, stating the probability of an atom to deexcite
back to a lower energy state. In the presence of an electromagnetic photon with the
appropriate wavenumber for a transition between two energy levels, the atom or
molecule can undergo an absorption transition. The third process takes place when
the atom is in its excited state and, in the presence of an electromagnetic photon, it
undergoes stimulated emission. Fig. 2.2 illustrates these three processes [8].
Fig. 2.2 Illustrating the three possible radiative processes for a two-level atom or molecule;
a) emission, b) absorption and c) stimulated emission.
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For gases at very high temperatures, the absorption of a photon may cause a so
called bound-free transition, in which the electron may break loose from the molecule
or even break the whole molecules apart due to strong vibrations. This is also called
ionization. The same process, but reversed, may occur with emission. Ionization
results in a continuous radiation, usually found in the ultraviolet and visible region.
The electrons in ionized gas may also interact by collisions with the electric fields of
the ions locations in a free-free transition, causing Bremsstrahlung radiation and
giving rise to continuous spectra [5]. For combustion applications bound-bound
transitions only will only considered.
Other none-radiative transitions may also occur, such as quenching when the
molecule or atom is deexcited without release of photons or through collision
between atoms or molecules.
2.1.2 Broadening of spectral lines
The radiation propagating through a gas is transformed by the absorption and
emission processes mentioned in the previous section. Emission and absorption lines
may occur at the same frequencies but have different intensity distribution. This
radiation is characterized by a spectrum of spectral lines with a certain molecular or
atomic configuration.
Spectral lines have a finite width; they may be broadened by different
processes. One of these is natural broadening because the excited state has a finite
lifetime and will eventually relax to lower state by spontaneous emission. As
consequence of Heisenberg’s uncertainty principle, when the atom relaxes back to its
original state, the energy release is slightly different. This small difference generates
a photon distribution around the differences of the two theoretical energy states of the
two-level system, which has a finite width called the natural line width [9]. The line
profile given by such broadening effect is a Lorentzian function.
Another broadening effect is the Doppler broadening. It arises from the
different thermal movements of the emitting atoms or molecules, creating spread of
Doppler shifts in the direction of the observer. The line profile representing this
spread is given by the Gaussian line profile.
Pressure broadening, also referred to as collision broadening, is another type of
broadening, and arises from interaction between the emitting or absorbing atom and
molecules in the gas. The effects arise from different types of perturbations, such as
charged or neutral particles. These perturbations will not be discussed in detail here
[8]. Pressure broadening gives rise to a Lorentzian line profile.
Sometimes these broadening effects occur simultaneously and are in the same
order. In such cases the Gaussian and the Lorentzian broadening profiles are
convoluted, creating a new line profile called the Voigt profile. The wings of a Voigt
profile often represent the Lorentzian and the center the Gaussian profile [10]. Fig.
2.3 illustrates the different line profiles.
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Fig. 2.3 Shows the three line profiles comparison with normalized intensity and the same width. [11].
2.2 The equation of radiative transfer
To relate the measured signal from a system with a variable of interest, such
as species concentration or temperature in a volume of gas, the equation of radiative
transfer may be used [10]. Fig. 2.4 shows an illustration of the optical system for
radiative transfer. A radiative emitter transmits in various or all angles depending on
the frequency of the light. One differs between irradiance Iv: [W/(cm2 cm
-1)] and
radiance Jv: [W/(cm2 sr cm
-1)][10].
Fig. 2.4 Illustration of the optical system for the radiative transfer.
The radiative transfer can be expressed in terms of the emission coefficient εv
and the absorption coefficient, kv, given by Eq. (2.2) [10]. The source function, Sv, is
defined as Eq. (2.3) and the total optical depth, τv, is defined as Eq. (2.4) with the
optical path length l.
vvvv Jzkz
dz
dJ)()( −= ε (2.2)
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v
vv
kS
ε≡ (2.3)
∫=l
vv dzzkl0
')'()(τ (2.4)
With these definitions, the radiative transfer equation can be re-written into Eq.
(2.5). If scattering is considered, the radiative transfer equation becomes much more
complicated and can only be solved numerically [12]. Hence if the extinction is
described by absorption and scattering, the radiative equation looks something like
Eq. (2.6). Where a(v) is the single scattering albedo which is the ratio of scattering
coefficient to the total extinction coefficient. The general solution of the equation of
radiative transfer, with no scattering, is given by Eq. (2.7) [10].
vv
v
v SJd
dJ=+
τ (2.5)
[ ] ∫ ΩΩ+−+−=+ π
νννν ω
πν
νττ
4
)ˆ,'ˆ('4
)()()(1
)(Jpd
aTSaj
d
dJ
absorptionscattering
(2.6)
∫−− +=)(
)0(
)()()()()()0()(
l
v
l
v
ll
vv
v
v
vvv zdezSeeJlJ
τ
τ
τττ τ (2.7)
In a combustion system the investigated medium is not always homogeneous,
but a path-averaged result is obtained in line-of-sight measurements. By assuming
homogeneity, one can simplify the radiative transfer equation further. In such
scenario the optical depth Eq. (2.4) and source function Eq. (2.3) is no longer
dependent of the optical path length z. The Eq. (2.7) is then simplified to Eq. (2.8)
and represents the light registered as a function of path length, as a result of the
absorption and the emission in the investigated system [10].
[ ]lk
v
lk
vvvv eSeJlJ
−− −+= 1)0()( (2.8)
The first term represents the absorption and the second term represents the
emission. As the photon reaches the gas cloud it may interact with the molecules and
atom by either being absorbed, emitted or scattered, however scattering of photons by
molecules is negligible for heat of transfer applications [5].
2.2.1 Absorption
In the case of a gas which is not emitting very strongly, the emissivity and
source functions can be approximated to zero. The solution to the equation of
radiative transfer, Eq. (2.8), then becomes the Beer-Lambert law, see Eq. (2.9). This
law describes the absorption of the radiation as a function of the distance through the
absorbers [10].
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lk
vvveJlJ
−= )0()( (2.9)
Here Jv(l ) describes the intensity transmitted and Jv(0) is the intensity before it
enters the absorbing medium. This equation can be used to obtain a linear relation
between the absorption intensity and the concentration. According to reference [13],
there might be some deviation from this linearity; for example, if there is scattering
of light due to particles, fluorescence or phosphorescence in the sample.
2.2.2 Emission
In the case of a very strong emitting gas, with no external light source,
J(0) = 0, and neglecting line-of-sight absorption, then Eq. (2.7) can be simplified to
only describe the emission. The emission is given by Eq. (2.10). This relation is not
dependent on the optical depth.
[ ]lk
vvveBlJ
−−= 1)( (2.10)
If the gas is optically thin, then τv(l) << 1 and a linear relation can exists
between the intensity and the number density of the emitting molecules or atoms. As
optical depth increases, the emission departs from linearity, and reaches a limiting
value when the emission equals the source function, i.e., when the emission starts to
acts as a blackbody. The gas is in this optically thick stage when τv(l) > 1. One can
then describe the emission by Eq. (2.11) where the radiation constants c1 is 1.191·e-12
[W cm2 sr
-1] and c2 is 1.438 [K cm] [10]. Equation (2.11) describes a true blackbody,
scaled with the emissivity. By assuming local thermal equilibrium (LTE), the
emission and absorption coefficient are functions of temperature and density only,
and the source function Sv is equal to the Planck function Bv due to the Kirchhoff law.
Then the source function in Eq. (2.3) becomes the blackbody. A black body is an
object that absorbs all electromagnetic radiation that it is in contact with and emits a
blackbody radiation in return and is only temperature dependent. For an object that is
not an ideal blackbody one mention the objects emissivity. The emissivity describes
an object’s ability to emit radiation. A true blackbody has emissivity equal to unity,
ε = 1, while a real object has emissivity less than one, ε < 1. It should be mentioned
that the gas will never act as a true blackbody radiator, not even the Sun is a true
blackbody.
[ ]1
11
/
3
1
/
3
1
22 −⋅−=
−⋅=⋅= −
−− Tvc
lk
Tvcvve
vce
e
vcBJ vεε (2.11)
Hence, if one has a blackbody emitter, the emission is only dependent on the
temperature of the gas and the light frequency. Otherwise, it is also dependent upon
the absorption coefficient and the optical path length. The emissivity is given by Eq.
(2.12) where the transmittance arises from the Beer-Lambert’s law.
( )lkJ
lJv
v
v −−=−= exp1)0(
)(1ε (2.12)
When considering measurements practical one has to consider the spectral
response of the measurement setup (includes the response from the lenses, the
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Susan Lindecrantz | LTH
window of the engine allowing in-situ measurements, the filter and other objects used
in the measurement setup).
2.3 Line-by-line gas radiation simulation
To be able to predict the thermal emission and absorption spectra a line-by-line
program was created in MATLAB based upon the HITRAN database. In the
following chapters the HITRAN and HITEMP database and its applications are
described. Afterwards the line-by-line models are used for the simulations in the
presented methods.
2.3.1 HITRAN/HITEMP database
HITRAN stands for high-resolution transmission molecular absorption
database. It is a compilation of spectroscopic parameters to be used to predict and
simulate the transmission and emission of light from a gas column. The database
stems from a long-running project started by the Air Force Cambridge Research
Laboratories in the late 1960's in response to the need for detailed knowledge of the
infrared properties of the atmosphere. In addition to HITRAN, which only covers the
line transitions accurately at temperature range below 1000K, there is another similar
database named HITEMP (high-temperature spectroscopic absorption parameters)
that covers temperatures in the range above 1000K. Both databases are being
constantly developed at the Atomic and Molecular Physics Division at Harvard-
Smithsonian Center for Astrophysics under the direction of Dr. Laurence S.
Rothman. The HITRAN database is recognized by many researches and used in
many different applications such as transmission simulations, fundamental laboratory
spectroscopy studies and combustion physics [14].
The latest edition, 2008 v13.0, of the HITRAN molecular spectroscopic
database is available on the website for the Smithsonian Astrophysical Observatory
in Cambridge, USA. The database contains line-by-line parameters which can be
compiled in the written software named JavaHAWKS which then can be processed in
MATLAB. The latest edition of the HITEMP database was in 1995; however,
according to Dr. Rothman a new version, will come out soon in the same format as
the current HITRAN [15]. Since flame’s temperatures often are above 1000K,
HITEMP can be useful in the research field of combustion physics, but the current
version of HITEMP is missing valuable data, such as the statistical weights and
Einstein coefficient. In addition HITEMP is only available for certain molecules like
CO2, CO and H2O.
It should also be noted that the newer version of the HITRAN is not completely
functional with JavaHAWKS, which was built for the 2004 version of HITRAN. This
is probably because the new HITRAN not only includes more precision for line-to-
line transitions, but also, additional isotopes of some species, which makes the
current software freeze for these isotopes when processing the new data. It is possible
to create one’s own JavaHAWKS version to work with the 2009 version, but that is
beyond this project. For this reason, the 2004 version of HITRAN and, whenever
possible, the 2009 version of HITRAN were used in the simulations.
The spectroscopic constants in the HITRAN databases are from different
sources and all have their own uncertainties stated in the database by different codes,
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see Table 1. The uncertainties are wavelength positions, half-widths and line intensity
strengths. These uncertainties have not been utilized in this report but should be
considered for further investigations.
Table 1 Illustrates the uncertainties of the HITRAN database. [15]
The 2004 edition of HITRAN contains line data for 39 molecules [14],
including their isotopes and the 2008 edition of HITRAN contains line data for 42
molecules [16]. Although primarily intended for atmospheric studies, important
combustion species are also included such as H2O, CO2, NO, NO2, OH and fuels
such as CH4 and C2H2.
2.3.2 Applications of HITRAN database
The following section will describe the different parameters and how HITRAN
is used for the line-to-line modelling [17]. The database contains the line strength,
S(T), which can be calculated from Eq. (2.13). The line strength values at
temperatures T can be corrected from the line strengths at the reference temperature,
296K, by using the relationship in Eq. (2.14).
( ) )/exp()/exp(1)(3
8),( 12
2
reflowerref
refref
ref kTEkThcvTTQ
P
hck
vvTS −−−ℜ=
π (2.13)
−−
−−
−
−=
)exp(1
)exp(1
)exp(
)exp(
)(
)(),(),(
2
2
2
2
refref
lower
lower
refref
ref
T
vc
T
vc
T
EcT
Ec
TQ
TQ
T
TvTSvTS (2.14)
S(Tref) is the spectral line intensity or line strength at reference temperature
[cm-1
/molecules cm-2
], c2 is the second radiant constant, v is the transition
wavenumber [cm-1
], Elower is the lower state energy [cm-1
], T is the temperature [K]
of the gas, Tref is the reference temperature at 296K, k is the Boltzmann’s constant, h
is the Planck constant, P is the pressure of the gas volume and Q(T) is the total
Line position and air pressure-
induced line shift (cm-1)
Intensity, half-width (air- and self-)
and temperature-dependence
Code
Uncertainty range
Code
Uncertainty range
0
> 1.0 or unreported
0
Unreported or unavailable
1 > 0.1 and < 1.0 1 Default or constant
2 > 0.01 and < 0.1 2 Average or estimate
3 > 0.001 and < 0.01 3 > 20%
4 > 0.0001 and < 0.001 4 > 10% and < 20%
5 > 0.00001 and < 0.0001 5 > 5% and < 10%
6 < 0.00001 6 > 2% and < 5%
7 > 1% and < 2%
8 > 1%
16 Chapter 2 – Background and Motivation
Susan Lindecrantz | LTH
internal partition sum given by the parasum.dat from HITRAN’s homepage. The line
strengths are tabulated in HITRAN with the unit [cm-1
/molecules cm-2
] and can be
converted into [cm-2
/atm] in Eq. (2.15) at reference point. The Eq. (2.14) may then be
used to correct the line strength for the temperature.
TcmmoleculescmSatmcmS
296102.68676)/()/( 19212 ⋅⋅⋅= −−− (2.15)
The value 2.68676 1019
[molecules/cm3 atm] is the Loschmidt number at STP
(standard conditions for temperature and pressure). The following procedure was
used for the conversion; all line strengths at reference point 296K where converted
and then this value was temperature corrected using (2.14). Pressure shift of the
transition wavenumber may occur, and is corrected by (2.16).
ppvv refcorr )(δ+= (2.16)
Where the δ(pref) is the air-broadened pressure shift [cm-1
/atm] and is given in
the HITRAN database. The HITRAN/HITEMP database provides air-broadening and
self-broadening half-widths for all lines listed in the database at the reference
temperature of 296K. The total coalitional broadening half width at half maximum
(HWHM) can be corrected for a given temperature and pressure with help of Eq.
(2.17).
srefrefselfsrefrefair
n
ref
L pTpppTpT
TTp ),())(,(),( γγγ +−
= (2.17)
The p is the total pressure of the gas [atm], temperature T [K] and partial
pressure ps [atm] of the gas. In this equation γair [cm-1
/atm] is the air-broadened
halfwidth at half maximum at Tref =296 K and pref at 1 atm, γself [cm-1
/atm] is the self-
broadened halfwidth at half maximum and n is the coefficient of temperature
dependence of the air-broadened halfwidth. In the engine cylinder there exists
elevated pressure changes during the combustion cycle and thereby should give rise
to collision-broadened spectral lines. This broadening is represented by the
Lorentzian (2.18).
22 )(
1
corrL
L
Lvv
f−+
=γ
γπ
(2.18)
In the engine’s cylinder the temperature is also elevated with every combustion
cycle giving cause for Doppler broadening, see in Eq. (2.19). This broadening is
represented by the Gaussian lineshape with a Doppler HWHM given by (2.20) with
molecular weight, M [a.m.u] at temperature, T.
−−=
2
2))(2ln(exp
2ln
D
o
D
D
vvf
γγπ (2.19)
MTvD /10581.3 0
7−×=γ (2.20)
Master of Science Thesis 17
LTH | Susan Lindecrantz
The Lorentz and Gaussian lineshapes can be combined in the Voigt line shape.
The Voigt profile is given by the following equations (2.21) [18].
∫∞
∞− −+
−==
=
dttxy
tyyxKA
yxAKf
D
v
22
2
)(
)exp(),(;
2ln1
);,(
ππγ
2ln;2ln)( 0
D
L
D
yvv
xγγ
γ=
−= (2.21)
Where γD and γL is the Doppler and pressure broadening half-widths at half-
maximum, v0 the transition wavenumber. The transmitted intensity, It, through a gas
can be related to the incident intensity at a certain wavenumber, Io, by Beer’s Law as
stated from the radiative transfer for the case of pure absorption. This can be
simulated using the HITRAN database where the Beer’s law is given by Eq. (2.9)
where the optical depth is given by,
LfvTSPxLk vvspeciesvv 0),( −==τ (2.22)
Here the kv [cm-1
] is the spectral absorption coefficient, L is the optical path
length of the absorbing medium, xspecies is the mole fraction of the absorbing species,
P is the total pressure of the gas mixture, S(T,v) is the line strength [cm-2
/ atm] at the
temperature T [K] and fv-v0 [cm] is the normalized lineshape function. Table 2 lists the
spectroscopic parameters and its units listed in the HITRAN database.
Table 2 Contains the spectroscopic parameters and units used in HITRAN 2004
and 2008 [16,15].
18 Chapter 2 – Background and Motivation
Susan Lindecrantz | LTH
2.4 Briefly about combustion
Combustion is a chemical processes between fuel and its oxidant which results
in heat and the conversion of chemical species. The release of heat in the conversions
results in what we know as a flame. Combustion takes place in a Bunsen burner and
in a spark-ignition engine. What characterize a flame is its high heat release reaching
over 2000K in combustion and the creation of soot particles [19].
There are two types of flames, the premixed flame and the diffusion flame. In
the premixed flame the fuel and the oxidant are mixed before combustion occurs. In
the diffusion flame the oxidant and the fuel are separated and do not mix until the
moment of the combustion. In fundamental research a flame without turbulence is
often required, the laminar flame. A premixed flame can be divided into the follow-
ing zones; unburned gas zone, preheat zone, reaction zone, and product zone. This is
illustrated in Fig. 2.5.
Fig. 2.5 Displaying the different zones in one dimensional premixed adiabatic flame along with the
concentrations and temperature profiles of the flame [20].
For a premixed flame in the preheated zone, the gas mixture is heated by heat
conduction from the reaction zone and only a small amount of heat is released by
chemical reactions. The separation of the preheat zone and the reaction zone is often
defined as the position at which there is an inflexion point in the temperature profile,
or the location of creation of intermediates. In the reaction zone there is a fast release
of energy which leads to a very steep temperature gradient. A visible flame front lies
within this reaction zone and it is therefore a good distinction of where the reaction
zone is located in a premixed laminar burner. It is in this region most reactions take
place. The location of the visible flame front depends on the pressure, flux speed and
composition of the mixture. Directly after the flame front, the products zone emerges
in which most reactions have already occurred and the products of the combustion
exist [20]. It is difficult to draw a distinct line between preheat and reaction zones but
it can be thought of as the point at which exothermic reactions become significant
and where the temperature profile is the steepest [21].
Master of Science Thesis 19
LTH | Susan Lindecrantz
For these projects, two different types of flames are considered, a lean and a
rich flame. The equivalence ratio, defined as Eq. (2.23), describes the flames
composition.
λ
ϕ1
_/#_#
_/#_#
_
_ ==mixturetricstoichiome
mixturereal
oxygenmolesfuelmoles
oxygenmolesfuelmoles (2.23)
Stoichiometric mixture represents an ideal combustion in which the fuel is
completely burned. Lean flames have excess of oxygen and their equivalence ratio is
less than one, φ < 1, while rich flames do not have enough oxygen to allow complete
combustion. Its equivalence ratio is greater than one, φ > 1. Another term often used
is the air-fuel-ratio, λ, and is defined as the inverse of the equivalence ratio. In this
project both lean and rich flame’s spectra are to be studied. Reaction formulas for
combustion of any fuel can be rather complicated since many subreactants may occur
before it reaches the stable end product. It is for this reason that reaction formulas are
not described in detail.
The global reaction of combustion of isooctane is shown as Eq. (2.24) [22].
Based upon this relation the reaction formula for methane and air is described as
(2.25).
222222188 16.47)1(5.1298)773.3(5.12 NOOHCONOHC +−++⇒++ λλ (2.24)
2222224 16.47)1(5.1221)773.3(5.12 NOOHCONOCH +−++⇒++ λλ (2.25)
λ is a measure of the mass ratio of air and fuel during the fresh charged inducted
through the intake [22].
2.5 Internal combustion engine
There are two main types of internal combustion engines commonly used, the spark
ignition (SI) and the compression ignition (IC) engine. For the spark ignition engine
the fuel is ignited by a spark and the timing of the combustion can easily be
controlled. In the compression ignition engine, the temperature and pressure rise
during compression to the point that it will induce an ignition of the fuel [23]. In this
project an engine with combination of the two was considered for the engine
simulation. This engine is called an HCCI (Homogeneous Charge Compression
Ignition) engine, which includes a spark plug to be able to control the ignition timing.
An HCCI engine is in general based on the four-stroke Otto cycle. The cycle
contains four reciprocating motions [24]. The first step is called the intake stroke,
where the piston moves down and air and fuel are pulled into the combustion
chamber. It is followed by the compression stroke, where the piston moves up and
the air and fuel is mixed and compressed. The next step is called the power stroke
and the fuel/air mixture is ignited and the piston is forced down. The cycle ends with
an exhaust stroke where the piston moves back up and get rid of the exhaust gases,
making way for a new intake stroke. See Fig. 2.6 for illustration of the process.
20 Chapter 2 – Background and Motivation
Susan Lindecrantz | LTH
Fig. 2.6 Illustrating the four stroke engine cycle presented in
Internal EGR (Exhaust Gas Recirculation) is when residual gas from the
previous cycle is trapped and mixed with fresh inducted charge. For an HCCI engine,
the mixing of the fresh charge and the reinducted products during the induction step
for lean or Stoichiometric
introducing the EGR [22].
2188
2188
)(5.12
773.3(5.12
OHC
NOHC
−−+
++
λααλ
λ
α = Negr / Nfresh is the ratio of the moles of
moles of the inducted fresh charge. Thus the
considered can be obtained from the following relationships [22],
60
188
188 +==
αλχ
total
CC
CCN
N
460
2
2 +==
αλχ
total
OH
OHN
N
Background and Motivation
Illustrating the four stroke engine cycle presented in the text [25].
Internal EGR (Exhaust Gas Recirculation) is when residual gas from the
previous cycle is trapped and mixed with fresh inducted charge. For an HCCI engine,
the mixing of the fresh charge and the reinducted products during the induction step
toichiometric, isooctane can be rewritten from Eq. (2.24) to (2.26)
[22].
2222
22222
)1(16.4798
16.47)1(5.1298)
NOHCO
NOOHCON
++++
⇒+−+++
αλαα
λα
is the ratio of the moles of reinducted product Negr
fresh charge. Thus the mole fractions with the internal EGR
considered can be obtained from the following relationships [22],
1605.4
1
+++ λα
1605.4
9
++ λαα
Internal EGR (Exhaust Gas Recirculation) is when residual gas from the
previous cycle is trapped and mixed with fresh inducted charge. For an HCCI engine,
the mixing of the fresh charge and the reinducted products during the induction step
Eq. (2.24) to (2.26) when
⇒ (2.26)
and Nfresh is the
s with the internal EGR
(2.27)
(2.28)
Master of Science Thesis 21
LTH | Susan Lindecrantz
Chapter 3 - Experimental equipment and considerations
This chapter describes the experimental setup behind the two different types of
investigations that were made for simulations in emission and absorption
spectroscopy. The first part involved a high resolution investigation of the spectra
properties of a laminar flame. The second part involved the usage of absorption and
emission simulations. In the following sections the setup of such possible
experiments is discussed.
3.1 Measurements with FTIR Spectrometer on a flame
In order to study the relationship between the emission and the concentrations
of a gas an experiment was arranged in which the emission of a premixed laminar
burner was captured and measured with a Fourier Transform Infrared Spectrometer
(FTIR Spectrometer). The data collected during these measurements is then used to
create simulation programs and to study the relation between concentration,
absorption and emission. Each spectral line is identified with help of the HITRAN or
HITEMP database.
3.1.1 Experimental setup
The experimental setup for this experiment is shown in Fig. 3.1; each part is
discussed in detail in the following chapters. He-Ne laser is used for alignment
between the burner, the slit and the aperture before the measurement. It was turned
off when the spectrometer recorded the flame emission.
Fig. 3.1 The experimental setup of the Fourier Transform Infrared Spectroscopy for the
flame measurement.
3.1.2 Burner
For the experiment, a premixed laminar burner was used to create lean and rich
premixed flame from the mix of the gases methane, nitrogen and oxygen. The
22 Chapter 3 - Experimental equipment and considerations
Susan Lindecrantz | LTH
respective flow velocities of the components are listed in table 3. The premixed
laminar burner is assumed to have a flat flame, meaning that the concentration of the
molecular and atoms occupying the area of the burners opening are relative uniform
at a particular height.
Table 3 The gas mixture of the flame with their respective gas flows in liter per min.
Fuel of the flame
[Liter per min]
Rich flame
[φ = 1.6]
Lean flame
[φ = 0.8]
Methane 3,115 1,558
Oxygen 3,896 3,896
Nitrogen 15,440 20,000
Co-flow 10,500 10,500
From the center of the burner, premixed gases of methane, oxygen and nitrogen
flow out and combustion takes place when the gas reaches the reaction zone. Around
the center a flow of nitrogen emerges. This co-flow protects the flame from any
disturbances like wind and combustion of surrounding air.
Fig. 3.2 The premixed laminar burner with a flame stabilizer on top and a tube ventilation system which
carries most of the burned gases outdoors. The red spot is the laser beam used for alignment into the
spectrometer.
Fig. 3.2 shows the premixed laminar burner used in the setup together with a
stabilizer which can prevent turbulence arises in the flame. A tube which leads
outside is placed on top of the flame so its exhaust fumes will not accumulate and
cause danger to the lab participants. The height of the burner was aligned with help
of a laser beam to place the burner at a height that the light emerging from the
measurement position of the flame comes through to the aperture of the instrument.
The burner was placed on an adjustable mounting, so it could move in the vertical
direction to the different measurements positions. A ruler was used to determine the
different heights from the flame zone. The burner was placed at twice the focal
length of the first mirror, 2f = 50 cm, which leads the light into the second mirror and
focusing it into spectrometers aperture. The diameter of the burner was 70 mm,
Master of Science Thesis 23
LTH | Susan Lindecrantz
which is assumed to be the optical path length of the gas investigated with no
scattering effects taking into account.
3.1.3 Slit
A slit was used to block most of the thermal light from the stabilizer and
surrounding metal surface near the flame and to block light from other regions of the
flame. A rectangle was cut away from a piece of metal, see Fig. 3.3. Five locations in
the flame were measured, one in the reaction zone, two locations below and two
locations above the reactions zone. A laser beam was used to align the measurement
location and the slit at the new height, enabling the spectrometer to collect the light
from the set flame height. In order to align the burner to the wanted positions the
burner was moved in correlation with the slit and the rest of the setup. The slit was
placed 5 cm from the burner and has a minimum of 2 mm aperture.
Fig. 3.3 Image showing the
design of the slit used in the
FTIR Spectrometer experiment
with an minimum aperture of
2 mm.
3.1.4 Fourier Transform Infrared Spectrometer
A spectrometer split the light into the different wavelengths components it
contains and the light intensity (number of photons) is measured as a function of the
wavelength. In the experiment, FTIR Spectrometer was used so the flames spectral
distribution in the infrared region could be recorded with a high resolution of 0.05
cm-1
. This data was later used to evaluate the emission simulation. The FTIR
Spectrometer is a Michelson interferometer with a movable mirror, see Fig. 3.4.
Light merging from the entrance aperture is split into two beams by a beam splitter;
one beam is reflected onto a fixed mirror and the other beam onto a moving mirror
which introduces a time delay in one of the beams [8].
Fig. 3.4 The figure shows principle of the Michelson interferometer.
24 Chapter 3 - Experimental equipment and considerations
Susan Lindecrantz | LTH
The detector registers the combined signal from the fixed and movable mirror
as a function of the path differences between the two beams, which is called an
interferogram; this is the Fourier transform of the spectrum. The spectrum can then
be obtained by taking the inverse Fourier transform of the signal [8]. For this
experiment the spectra is recorded with the FTIR Spectrometer of model type IFS
125 HR by Bruker Optics, see Fig. 3.5.
Fig. 3.5 The figure shows the Fourier Transform Infrared Spectrometer used in the space experiment
from the Atomic Astrophysics department in Lund University.
A program called OPUS was used to process the recorded signal and Fourier
transform the interferogram into a spectrum. Fig. 3.6 displays the interior layout of
the spectrometer in which one can recognize the Michelson interferometer from Fig.
3.4. The detector used inside the spectrometer is made of InSb and the beam splitters
of CaF2.
Fig. 3.6 The figure shows layout of the spectrometer used in the experiment.
Master of Science Thesis 25
LTH | Susan Lindecrantz
Two external mirrors outside the spectrometer opening are used to direct the
light source into the aperture of the spectrometer, so the signal can be processed and
recorded. Since light with different wavenumber responds differently to the optical
components within the spectrometer one has to consider the spectrometer’s response
function when analyzing the spectrum. For this experiment the aperture to the
spectrometer was set to 1.5 mm. For the blackbody measurement the opening was set
to 0.5 mm since a bigger aperture proved to give a saturated spectrum. For each
measurement, 20 a scans were made, to obtain an average value of the intensity.
3.2 Engine experiment proposal
Without a spectrometer, the integrated emission intensity can be collected with
an ordinary detector. This intensity can then be compared with the simulations of the
integrated intensity dependent on either the concentration or temperature. The
spreading of the spectral lines according to their line profile often results in overlaps
between the multiple lines. The same goes if an overlap exists between spectral lines
of different species located at the same wavenumbers. With no spectrometer, the
spectral lines cannot be resolved for emission spectroscopy. In absorption
spectroscopy a light source is used to determine the transmission from the
experiment. If the light source is monochromatic and tunable, the transmission as a
function of wavelength can be obtained.
3.2.1 Experimental setup
The suggested experimental setup for this experiment is shown in Fig. 3.7,
each part is discussed in detail in the following chapters; Fig. 3.7a) and 3.7b) consists
of a setup for the absorption measurements using a diode laser and LED respectively.
Fig. 3.7c) consists of a setup for thermal emission measurements.
a) b)
26 Chapter 3 - Experimental equipment and considerations
Susan Lindecrantz | LTH
Fig. 3.7 A simple illustration of the three possible measurements setup with the engine.
Image a) represents the absorption measurement using diode laser and b) using an LED with the same
setup. Image c) represents the thermal emission measurement.
3.2.2 Possible light sources
The engine part of this report deals with two different tasks, one part is to
estimate the temperature and the second part is then to determine the concentration.
The information about the temperature can be extracted with help of the radiative
transfer relation applied for two optical thick bands. The bands investigated for this
purpose are the CO2 band around 2250-2450 cm-1
and the CO2 band around 3450-
3915 cm-1
. The band at 3450-3915 cm-1
also included water lines which have been
accounted for in the simulations.
Two detectors are placed in front of each filter and a collimator, to focus the
thermal light into the detector and register only the spectral region which is
transmitted through the filter. The task is to determine the concentration of CO2 with
help of absorption or emission. The band investigated for this purpose is the CO2
band around 4840-4925 cm-1
. These regions have been chosen with respect to
available filters.
Measurement of the transmission gives the concentration of the investigated
species with help of Beer’s law. For this purpose the choice of the light source and
wavelength of the investigated region is important. The absorption must take place at
the wavelength in which transitions exist; otherwise there will be no absorption.
One of the light sources for the absorption measurement considered in this
thesis is a light emitting diode (LED). The main function of any diode is to direct
current in one direction. A diode is essentially a semiconductor and contains an
anode and cathode. When an electron moves from the n-type side to the p-type side,
the energy difference of these two levels is the energy that is emitted in form of a
photon with a certain frequency. By using different atoms to dope the material in the
semiconductor, different energy level differences can be obtained and thus different
colors of the LED can be generated [26].
In these simulations the LED chosen is called LED20, which is designed for
emitting at a spectral range around 2050 nm. From the HITRAN database it has been
verified that within this region there exists an optically thin band of CO2, clear from
water lines, especially at low temperatures. The LED emits a broadband light, see
Fig. 3.8. The LED is said to have stable output power and lifetime over 10000 hours
[27].
c)
Master of Science Thesis 27
LTH | Susan Lindecrantz
Fig. 3.8 The figure shows the typical line profile at different temperatures for the LED investigated. [27].
Another light source that can be considered is the diode laser, emitting
monochromatic light. For this experiment a mid IR-laser tunable diode was
considered. According to ‘Roithner Laser Technique’, one of many diode laser
providers, custom wavelengths from 1.8-2.6 µm are available on request [28].
3.2.3 Filters
A narrow band pass filter is placed in front of the detector in order to only
register intensities from the spectral region within the band regions of interest. A
filter was chosen for each band region under investigation. An ideal filter includes no
absorption from CO2 and H2O in the surrounding air during the measurement of
desired wavenumbers. This is however difficult to achieve, for example, the
fundamental band of CO2 showed apparent absorption lines from the air (see chapter
5.1). The selection was based on the possibility of measuring CO2 at best without
H2O interference and the locations of the CO2 bands and availability from the
manufacture. At the location of the main fundamental band a filter called NB-4235-
082 was chosen. This filter has a center wavelength (CWL) of 2361 cm-1
and a half
width at half maximum (HWHM) of 46.7 cm-1
, see Fig. 3.9 c), and the peak
transmission is 90.22%. For the first combination band of CO2 a filter called
NB-2690-050 was chosen. This filter has a center wavelength of 3691.8 cm-1
and a
HFHM of 69.1 cm-1
, sees in Fig. 3.9 a) and the peak transmission is 89.99%. For the
second combination band of CO2 a filter called NB-2050-012 was chosen. This filter
has a center wavelength of 4881.8 cm-1
and HFHM of 27.1 cm-1
, see Fig. 3.9 b) and
the peak transmission is 79.86%.
28 Chapter 3 - Experimental equipment and considerations
Susan Lindecrantz | LTH
Fig. 3.9 The figure illustrates the three filters transmittance profile. Figure a) displays an transmitt-
ance curve around 3600-3800 cm-1
, b) an transmittance curve around 4840-4949 cm-1
and c) an
transmittance curve around 2300-2450 cm-1
.
3.2.4 Engine
The engine intended for this project was based on a Volvo D5 diesel engine
operating on one cylinder, see Fig. 3.10. The engine has been modified to operate
with SACI combustion, an HCCI engine with a spark plug. The fuel considered for
these simulations is isooctane. The combustion chamber of the engine contains two
sapphire windows on opposite sides, enabling line-of-sight access through the engine
chamber, near the spark plug. With this engine it is possible to measure cycle to cycle
variations of the intensity. In the measurements, the hot spark plug might be a source
of interference since it is in the field of view. To avoid the spark plug acting as a
main emitter it can be physically blocked from view in the line-of-sight measurement
and thus minimize its interference with the surrounding gas in the chamber. This is a
rather big engine, and when using a fiber to collect the intensity to the detector, the
problems arising such as the fiber falling off due to the engine turbulence when
running should be negligible. For the simulations, the engine is expected to be
running on a lean fuel mixture, air-fuel-ratio between 1.2 and 1.6 with no EGR
accounted for. The changes of the λ due to the internal EGR are stated according to
Eq. (2.26). Two optical windows at opposite sides are required for the concentration
measurement.
4840 4860 4880 4900 4920 49400
20
40
60
80
100Transmission curve for filter NB-2050-012
Wavenumber [ cm-1 ]
Transmission [ %
]
3400 3500 3600 3700 3800 3900 40000
10
20
30
40
50
60
70
80
90
100Transmission curve for filter NB-2690-050
Wavenumber [ cm-1 ]
Transmission [ %
]
2250 2300 2350 2400 2450 25000
20
40
60
80
100Transmission curve for filter NB-4235-082
Wavenumber [ cm-1 ]
Transmission [ %
]
a) b)
c)
Fig. 3.10 The figure illustrates the engine considered for this
between a collimator and the engine
been placed in front of the detector to only detect light at a certain wavelength band.
3.2.5 Detectors
Fig. 3.11 shows the different types of materials for
According to [29] certain criteria need
must be registering at the wavenumber of interest, sensitive enough to register the
signal and fulfilling other
Fig. 3.11 The figure shows the sensitivities of the different types of detector materials in function of
the wave length [30].
A detector consisting of
since it has a high sensitivit
Master of Science Thesis
LTH |
The figure illustrates the engine considered for this project. A paper tube has been
een a collimator and the engine opening to minimize light interference from the room. A filter has
been placed in front of the detector to only detect light at a certain wavelength band.
Fig. 3.11 shows the different types of materials for the photodiode detector.
g to [29] certain criteria need to be considered when choosing a detector; it
must be registering at the wavenumber of interest, sensitive enough to register the
signal and fulfilling other requirements such as pricing and availability.
The figure shows the sensitivities of the different types of detector materials in function of
A detector consisting of Indium antimonite (Insb) is suggested for the purpose
since it has a high sensitivity of the range of interest and is available. For the thermal
Master of Science Thesis 29
| Susan Lindecrantz
project. A paper tube has been placed
opening to minimize light interference from the room. A filter has
been placed in front of the detector to only detect light at a certain wavelength band.
the photodiode detector.
to be considered when choosing a detector; it
must be registering at the wavenumber of interest, sensitive enough to register the
availability.
The figure shows the sensitivities of the different types of detector materials in function of
is suggested for the purpose
y of the range of interest and is available. For the thermal
30
Susan Lindecrantz | LTH
emission measurement two detectors are needed, where the line-of-slight intensity
splits onto two detectors by a beamsplitter. Each detector is equipped with a
collimator that transmits IR light and focuses the light onto the detector. For the line-
of-sight measurement of the intensity, two filters are placed in front of the detector.
For the second part, the signal from an LED and diode laser is registered with a
detector before and after the light is sent through the chamber.
Master of Science Thesis 31
LTH | Susan Lindecrantz
Chapter 4 - Measurement and Simulations
4.1 Introduction
In this chapter the code for emission simulations in MATLAB (MATrix
LABoratory) was created and compared with measurements [31]. The data required
for the calculation of the ‘synthetic’ spectra such as line positions, line strength
intensities and line broadening coefficients, can be taken from the spectral database
HITRAN or HITEMP depending on the temperature ranges used. The setup of such
an experiment is discussed, as well as the construction and implementation of the
simulation programs.
The first application is the emission of a flame from a porous-plug burner. The
light is collected into an Infrared Fourier Transform Spectrometer at Lund
Observatory, and its spectrum is recorded at different locations around the visible
flame zone located in the reaction zone. This spectrum is compared with the
simulated emission using the database.
The second application will use the simulation of the emission or absorption to
extract the temperature and, if possible, the CO2 concentration just before the fuel in
the engine is ignited. The ultimate goal is to find a method to determine how much
CO2 is recycled within the engine per ignition cycle. Comparisons between the
measured and calculated spectra can be made when possible.
4.2 Investigation and modelling infrared spectra in a flat
flame
In order to study the spectra from a flame and the relationship between the
emission, the concentration and the temperature of a gas, an experiment was
arranged. The emission of a premixed laminar burner was recorded with an FTIR
Spectrometer.
4.2.1 Experiment setup
After arranging the setup as described in the previous chapter, five height
positions above the burner were measured, see Fig. 4.1. Their positions were located
in the visible flame zone, above and below, 1 mm and 3 mm from the visible flame
zone respectively. The premixed flame is assumed to have a temperature between
300K and 2000K based on the chemistry modelling. These five measurements are
repeated for a lean flame with φ = 0.8 and for a rich flame with φ = 1.6. One
measurement was also done for a blackbody radiator at the temperature of 1473.15K
chosen arbitrarily.
32 Chapter 4 - Measurement and Simulations
Susan Lindecrantz | LTH
Fig. 4.1 Shows the setup for the flame measurement.
The aperture of the instrument was set to 1.5 mm for the two different flame
types and 0.5 mm for the measurement of the blackbody due to saturation of the
signal. In each measurement, 20 scans with the movable mirror in the FTIR
Spectrometer were made. The computer program later took an average of these scans
to produce the measured spectra of the flame emission.
4.2.2 Construction and simulation of flame spectra
In the following section a short description of the construction and
implementation of the simulations is presented. To simulate the emission, the theory
of the radiative transfer is used with the simplification of assuming scattering effects
negligible. Rayleight-scattering is much stronger than Raman, but can also be
considered insignificant in the infrared region since the intensity of scattered light is
inversely proportional to the fourth power of the wavelength, and linearly dependent
on the number density. If particles exist in the system the Mie scattering have to be
taken into account, which is considerable stronger than the Raman and the Rayleight
scattering. In the case of the premixed laminar burner, no particles enter the burner,
since the gas is filtered. Although particles can be formed during combustion, in form
of soot, this if often only the case for rich diffusions flames. In the engine combustion
chamber there might be a smaller amount of particles, but since the engine is running
on a very lean fuel, this effect is ignored in this initial investigation. In the case of the
engine, the amount of particles could be minimized further by filtering out the
particles during induction stage. In the flame the Raman- and Rayleight scattering
always exists. Since the Raman scattering often is very weak, on the order of 1000
times weaker than Rayleight scattering, this effect is considered small in combustion.
For these reasons the scattering has been assumed to be negligible for this initial
investigation of the radiative transfer. In addition the gas is also assumed to be in
local thermal equilibrium (LTE) and homogenous.
Master of Science Thesis 33
LTH | Susan Lindecrantz
The spectra recorded with the FTIR spectrometer are saved into files
containing two columns, the wavenumber and the intensity from the measurement.
The instruments used in the spectrometer give rise to a response function. It is the
collected response from the instruments inside the spectrometer which is determined
from measuring the spectra of the thermal lamp, approximately a blackbody source.
This spectrum is compared with the calculated Planck function with known
temperature. A thermometer measured the temperature of the blackbody source to be
1473.15 K. The response function can be determined in Eq. (4.1) and divided from
the measured flame spectra in Eq. (4.2).
BlackbodyCalculated
ackbodyMeasuredBl
FunctionsponseI
II =Re
(4.1)
Functionsponse
ectraMeasuredSp
spectraI
II
Re
= (4.2)
A Matlab program was created to process the data, named
CallProcessFTIRSpectraFunc.m, see Appendix A.1, in which the data from the
measurements was uploaded into vectors, and the response function removed from
the spectra as described above. The light from the flame also travels in the air
between the flame and the spectrometer. Due to this, the spectra obtained are
expected to contain absorption lines. This has been eliminated by fitting the
curvature of the measured blackbody.
The possibility of using a Voigt profile was also studied since the line profile is
often used in combustion applications. Due to the difficulty to evaluate the Voigt
formula, see Eq. (2.21), many approximations of the Voigt profile have been
suggested. One of them is given by Whitting [32] and another one is given by Yuyan
Liu [33]. Both of these Voigt approximations were investigated. A Lorentzian line
profile has been used for the spectral simulations since the Voigt line profile could
not be verified due to inaccessibility of available data for a true Voigt line profile.
Two different functions were created to simulate emission using Eq. (2.10)
valid for both optical thick and thin mediums. A function, called
CallOpticalDepthFunc.m, calculates the optical depth of the investigated species
according to Eq. (2.22). This result is used in the second function called
CallEmissionFunc.m, which uploads the HITRAN or HITEMP file created in
JavaHAWKS into vectors. The HWHM is calculated with Eq. (2.17) and calls
CallOpticalDepthFunc.m, which returns the optical depth of the spectral region for
the investigated species. The emissivity accordingly to Eq. (2.12) is determined and
multiplied with the Planck function to produce the emission spectra. The emission
function in the end returns the optical depth, the emissivity and the emission. See
Appendix A.2, A.3 and A.4 for the written programs.
The resolution of the spectra has been set to 0.02 cm-1
and is calculated
between the region 1500 cm-1
and 6000 cm-1
at the atmospheric pressure. For these
simulations the partial pressures and the temperature are assumed to be known.
These parameters were calculated by a modelling program named CHEMKIN, a
software tool for solving complex chemical kinetics problems. Table 4 shows the
result from the mole fraction and temperature simulation for the species investigated
34 Chapter 4 - Measurement and Simulations
Susan Lindecrantz | LTH
for this flame. The species chosen for investigation are the main species expected in
the IR region for the flame, such as CO2, CO, H2O and CH4. Once the visible flame
zone was identified in the CHEMKIN simulation, the other measurement locations
were also identified from this position.
Table 4 Illustrate the calculated mole fractions and temperatures for the respective
investigated species versus the flame coordinates using CHEMKIN.
Position from the
visible flame zone
[mm]
- 3 mm - 1 mm 0 mm + 1 mm + 3 mm
Flame coordinates in
plot [mm] -1.3 0.7071 2.32 3.33 5.25
Estimated
temperature [K] 300 398 1597 1669 1693
Φ = 0,8
CH4 0.061 0.0556 3.73E-06 6.61E-12 1.03E-18
O2 0.1525 0.1455 0.035 0.032 0.031
CO 8.71E-05 0.00133 0.0061 0.0013 0.00033
CO2 4.21E-05 0.0012 0.054 0.059 0.06
H2O 0.001 0.0122 0.1168 0.12 0.1216
N2 0.7848 0.7819 0.7828 0.7848 0.7855
SUM 0.9994292 0.99773 0.994707 0.9971 0.99843
Flame coordinates in
plot [mm] 0.5051 2.525 3.53 4.545 6.566
Estimated
temperature [K] 358 1353 1752 1794 1799
Φ = 1.6
CH4 0.1294 0.0446 0.0088 0.00572 0.004604
O2 0.1645 0.05887 0.0056 0.000778 5.75E-05
CO 0.0023 0.0513 0.0754 0.0753 0.074
CO2 0.000331 0.0154 0.03 0.0348 0.0379
H2O 0.009795 0.1271 0.1715 0.1723 0.1695
N2 0.6699 0.6388 0.6347 0.6347 0.6347
SUM 0.976226 0.93607 0.926 0.923598 0.9207615
Adding the partial mole fractions of each species at a certain measurement
location should equal one. It can be noted that, for the lean flame, the sum of the
species listed is almost equal to one but for the rich flame there is at most 8 %
difference from total concentration, indicating there might be species that are not
considered in this investigation. After further investigation this minor contribution
comes from species like CH2O, C2H2, CH3 that are created during or after the
reaction zone. For the lean flame these species are not of importance.
With help of a ray tracing program [34] the light path to setup was
investigated. The setup in the ray tracing simulation was simplified with a lens with
the same diameter and focal length as the mirrors used in the setup. The result gave
the same amount in number of photons in the spectrometer aperture as sent out from
the modelled light source. Different placements of the light source in the location
within the burner diameter did not change the results, for line-of-sight measurements.
Master of Science Thesis 35
LTH | Susan Lindecrantz
This indicates that the aperture is big enough to let through all photons released from
the gas column in the burner. The investigation didn’t tell anything more about the
actual optical length for the flame measurement, but with no scattering considered,
the optical path length has been assumed for light-in-sight measurement to be the full
length of the gas column in of the burner, which is 7 cm.
4.2.3 Discussion of the flame investigation and simulation
Fig. 4.2 below illustrates the flame front above the premixed laminar burner
during measurement. The flame front consists of a stable layer of light blue color.
This is the visible flame zone and exists within the reaction zone. The flame does
not show any yellow light, indicating that no soot or very little soot is created during
this combustion. If soot existed the flame zone would be yellow in color.
Fig. 4.2 Illustrates the visible flame zone during the measurements, in which the positions of the
measurements locations was derived from.
The spectra from the premixed flame was recorded and processed to obtain the
‘true’ spectra without the response function. The same setup was used to measure
blackbody emission at 1473.15 K, its spectra is displayed in Fig. 4.3.
36 Chapter 4 - Measurement and Simulations
Susan Lindecrantz | LTH
Fig. 4.3 Shows the measured spectra, fitted curve of the measured spectra and the calculated
blackbody spectra for T = 1473.15 K. The calculated Planck function was corrected to fit the
measured curve with an arbitrary value.
Fig. 4.4 Displaying the effect of the sensitivity drop-off from the detector on the blackbody spectra
from Fig. 4.3 (zoomed).
This spectrum contains H2O and CO2 absorption lines, which arise when the
light from the flame passed the cold air layer between the spectrometer and the
lightsource. There is a dip between 2900-3500 cm-1
which is not saturated like the
other absorption lines despite being very deep. For this reason this structure has been
assumed to be part of the response function of the instrument and not due to
absorption. The blackbody spectrum was to remove these absorption lines and then
expanded at lower wavenumbers since the spectrometers sensitivity falls off in this
area. Fig. 4.4 shows this drop-off in which the sensitivity seems to fall off rapidly
1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
measured blackbody curve
curve fitting of the measured blackbody
calculated Planck function with T = 1473.15 K
1650 1700 1750 1800 1850 1900 1950 2000 2050 2100
0
0.05
0.1
0.15
0.2
0.25
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
measured blackbody curve
curve fitting of the measured blackbody
calculated Planck function with T = 1473.15 K
Master of Science Thesis 37
LTH | Susan Lindecrantz
around 1850 cm-1
. This is consistent with the detector’s material sensitivity curve for
InSb. In Fig. 3.11 the InSb curve falls off drastically after 5µm (2000 cm-1
). For this
reason the spectra in this region are not very reliable, this is clearly shown in
Appendix C when the simulated and the measured spectra are compared.
Fig. 4.5 displays the resulting response function after using Eq. (4.1) for the
measured (red dotted line in Fig. 4.3) and the calculated blackbody spectrum (green
line in Fig. 4.3).
Fig. 4.5 Shows the resulting response function from Eq. (4.1).
Using the response function from Fig. 4.5 the true spectra for the premixed
methane/air flame is obtained with Eq. (4.2). The resulting spectra for the two flames
are displayed in Fig. 4.6. There are notable differences between the lean and the rich
flame. The spectra for lean flame below the visible flame zone shows less emission
and contains more static noise than the other spectral points for the same flame. This
apparent spectral noise could be explained by lower temperatures are thus less
emission and the existence of fluid gas before the reaction zone. For the spectra at
the visible flame zone, the CO2 band becomes more apparent and there is a CO band
just becoming visible. The spectra above the visible flame zone show very strong
water lines and CO2 band while the CO band is no longer clearly visible in
comparison, as shown in Fig. 4.6. This is expected for the lean flame since according
to the CHEMKIN, the CO is created near the visible flame zone and then disappears
afterwards as it is transformed into CO2. In the fundamental band of CO2 there are
very strong absorption lines, this is the same for all spectra. There is a band structure
from the CH4 that has been identified around 3000 cm-1
. The CH4 band seems to only
exist at the visible flame zone for the lean flame. There is no indication that this band
exist before the visible flame zone, possibly since the CH4 exists here as fluid gas
and has not been heated enough to produce emission bands. After the visible flame
zone this structure seems to have disappeared again. Since, in a lean flame, there
1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 650040
60
80
100
120
140
160
180
Wavenumber [ cm-1 ]
Response function [ - ]
38 Chapter 4 - Measurement and Simulations
Susan Lindecrantz | LTH
exists an excess of oxygen, indicating that all fuel will have been transferred into
products after the visible flame zone.
Fig. 4.6 Shows the comparison between the different measured locations of the flame spectra with φ = 0.8 and φ = 1.6.
The rich flame shows apparent emission spectra for all measurements heights
except 3 mm below the visible flame zone, indicating that the rich flame is much
hotter than the lean flame. It is also possible that it has a much larger reaction zone or
is located closer to the burner surface than the lean flame. In the rich flame, the CO
band emission is very strong and stays strong even above the visible flame zone,
indicating that CO has survived into the product zone. The CH4 band show a very
2000 2500 3000 3500 4000 4500 5000 5500
0
1
2
3
4
5
6
x 10-4
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Measured spectra from a flame with phi =0.8
2000 2500 3000 3500 4000 4500 5000 5500
0
2
4
6
8
10
x 10-4
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
3 mm above the visible flamezone
1 mm above the visible flamezone
at the visible flamezone
at the visible flamezone
1 mm below the visible flamezone
3 mm below the visible flamezone
H2O + CO
2
H2O
H2O
CO
CO2
CO2
H2O + CO
2
H2O + CO
2
H2O + CO
2
CH4
CH4
CO
2000 2500 3000 3500 4000 4500 5000 5500
0
2
4
6
8
10
x 10-4
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Measured spectra from a flame with phi = 1.6
2000 2500 3000 3500 4000 4500 5000 5500
0
2
4
6
8
10
12
14
x 10-4
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
at the visible flamezone
1 mm below visible flamezone
3 mm below visible flamezone
3 mm above visible flamezone
1 mm above visible flamezone
at the visible flamezone
CH4 H
2O + CO
2
H2O + CO
2CH
4
H2O + CO
2
H2O + CO
2
CO
CO
CO2
CO2
CO
H2O
CO
H2O
Master of Science Thesis 39
LTH | Susan Lindecrantz
clear band structure for the lean flame at 1 mm below the visible flame zone and
shows a less clear band structure at the visible flame zone in comparison, indicating a
decrease of the concentration of CH4.
For the plots for 3 mm below the reaction zone, the two different flame spectra
show little emission. Because of this, the noise level of the signal is very apparent
and lays around 10-5
to 10-6
a.u, shown in Fig. 4.7. This noise level of the signal
exists in all spectra. The only difference is that it is more prominent here due to the
lower emission levels. For the rich flame, the CO band emerges around 2140 cm-1
from the cold flame structure, indicating that CO is already formed here from the
heat of the reaction zone. Very few water lines are shown.
Fig. 4.7 Shows the comparison between the flame spectra for 1 mm and 3 mm below the visible
flame zone for φ = 0.8 and φ = 1.6.
From the plots 1 mm below, the lean flame shows similar spectra as for the
previous spectra while the rich flame shows strong emission lines for CO2, H2O and
CO. The rich flame also indicates a structure from the CH4 band at 3000 cm-1
, see
Fig. 4.6. This CH4 structure appears very strong for the rich flame at this location. As
previous stated only the rich flame at 1 mm below the visible flame zone shows this
structure. This is due to that there is more fluid gas as actual emission of the CH4
molecules. The CH4 molecules must be heated enough to be excited to higher
excitation states and thus no photons emitted to be registered by the spectrometer of
this band. The rich flame shows a relative strong CO band around 2140 cm-1
but
there are also some CO band heads around 4350 cm-1
and 4300 cm-1
.
At the visible flame zone for the lean flame a CO structure is emerging, but the
CO band head is still not visible compared to the rich flame. Both flames show the
CH4 structure indicating that there is still some fuel in this region, even if it is much
weaker than previous measurement locations.
For plots 1 mm above, the lean flame is missing the CO band at 2140 cm-1
; see
Fig. 4.6, indicating that the CO radical have already been consumed in the product
zone. At this point the fuel lines have disappeared from the structure for both flames.
2000 2500 3000 3500 4000 4500 5000 5500
0
1
2
3
4
5
6
7x 10
-5
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Measured spectra from a flame with phi = 0.8
2000 2500 3000 3500 4000 4500 5000 5500
0
1
2
3
4
5
x 10-4
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Measured spectra from a flame with phi = 1.6
1 mm below visible flamezone
3 mm below visible flamezone
1 mm below visible flamezone
3 mm below visible flamezone
40 Chapter 4 - Measurement and Simulations
Susan Lindecrantz | LTH
For plots 3 mm above, around 1850 cm-1
there are some water lines. These
lines are very apparent for the lean flame because the CO band at that region is
missing, while for the rich flame, some CO has survived. Both flames contain strong
band structures from H2O, although it is slightly stronger for the rich flame.
The two bands around 2000 cm-1
show a certain shift of the baseline. This is of
course due to the many lines in the area being added together; however, this structure
is very strong even at the lower wavenumber for the CO band. This feature is either
showing the beginning of the formation of a blackbody radiative curve or is due to
the large number of lines in the region. However, this structure is even shown for
spectra below the visible flame zone, where no or little emission exists.
The investigated species within this region in the previous plots have been
identified from the simulations; Fig. 4.8 shows an example of the identification. The
CO band around 3000 cm-1
and the CO2 around 5000 cm-1
is not visible in this plot
because they are too weak in the simulation to be displayed.
Fig. 4.8 Shows an example of a study of the investigated species locations for the flame with φ = 1.6.
Fig. 4.9 shows some examples of the comparison between the measured and
the simulated spectra. The comparison between the simulated and the measured
spectra for all locations can be found in Appendix C. It should be noted that no
corrections have been made between the simulated and the measured spectra.
2000 2500 3000 3500 4000 4500 5000 5500
0
2
4
6
8
10
x 10-4 Spectra for phi = 1.6 flame at visible reactionzone - Identification of the species
Intensity [ cm-1 ]
Wavenumber [ cm-1 ]
2000 2500 3000 3500 4000 4500 5000 5500
0
0.5
1
1.5
2
2.5
x 10-3
Wavenumber [ cm-1 ]
Intensity [ cm-1 ]
measured spectra
H2O
measured spectra
CO2
CO
CH4
Master of Science Thesis 41
LTH | Susan Lindecrantz
Fig. 4.9 Shows the two examples of features in comparison between the flame spectra for 1 mm
above the visible flame zone for φ = 0.8 and φ = 1.6. The upper image shows the band head of the
fundamental CO2 (to the right) and the CO2 absorption lines (to the left). The lower image shows part
of the combination band of H2O.
It can be noticed that in terms of line position, the simulated spectra fit well to
the measured, however the line strengths are sometimes much greater or smaller for
the simulation for some species and flame locations. Uncertainties in the
spectroscopic database might be a source for the spectra’s fit not being perfect. This
could be that the CHEMKIN models a flame that is perfect laminar and adiabatic.
However in reality, the flame is not perfectly adiabatic since there will always be
heat loss to the environment. The burner has a stabilizer above the flame which
deviate the flame from perfect laminar. This is especially true at the edges of the
visible flame zone, seen in Fig. 4.2. For example in the plot 1 mm above, for the rich
flame, the CO band seems to be missing in the simulation. In the same plot the H2O
lines seem to be much bigger; however, this could be a result of partial or full
absorption in the band, see Fig. 4.10 and Appendix C. The possible reason why some
of the lines seem to fit well while some are partial or completely absorbed, is that the
absorbing medium is cold and thus can only excite certain populations in the
molecules: the ground state transitions. As given from the Boltzmann distribution,
when the temperature increases, higher populations are occupied. This phenomenon
is also seen for the fundamental band of CO2.
2380 2381 2382 2383 2384 2385 2386 2387 2388 2389
0
0.5
1
1.5
2
x 10-3
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Example of comparison between measured and simulated spectra for phi = 0.8 at 1 mm above the visible flamezone
3475 3480 3485 34900
0.5
1
1.5
2
x 10-3
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Example of comparison between measured and simulated spectra for phi = 1.6 at 1 mm above the visible flamezone
simulated spectra
measured spectra
simulated spectra
measured spectra
42 Chapter 4 - Measurement and Simulations
Susan Lindecrantz | LTH
Fig. 4.10 Shows the two examples of features in comparison between the flame spectra for 1 mm
above the visible flame zone for φ = 0.8 and φ = 1.6. The upper image shows the combination band
of H2O in which some lines have been absorbed. The lower image shows part of the combination band
of H2O.
The simulated spectra of 3 mm below the visible flame zone, in both flames,
shows very little agreement with the simulated spectra. This is because we do not
have much emission in this region due to low temperature and concentrations in the
simulations. For the plots in the visible flame zone, the CO seems to be
underestimated for both lean and rich flame. The only plot that has visible CO band
in the simulation is the 1mm below the visible flame zone for the rich flame, and it is
seem to be bigger than the measured CO band. This is an indication that the either
the temperature or the concentration is not accurate with the measurement for some
species like CO. The simulation was based upon the given mole fractions and the
temperature calculated from the program CHEMKIN. It is clear from the
measurement and the simulated emission that some lines should be more prominent,
but is in the simulation too weak to be comparable with the CO2 band and water
lines, especially for higher temperatures. A possibility is that the CHEMKIN was
provided with too low concentrations or incorrect temperatures to give a perfect fit.
Another possibility is that since the simulations with over 1000K have been
simulated with HITEMP95 lines can be missing in the database for CO, CO2 and
H2O. Most of the H2O and the CO2 lines in the measured spectra seem to be weaker
since there is absorption. It is difficult to determine if it is a good fit or not, due to the
large amount of absorption in the fundamental band of the CO2 and the combination
band of H2O. The species of N2 and O2 are too small in comparison with the other
features, and they do not appear together with the other species.
3670 3672 3674 3676 3678 3680 3682 3684 3686 3688
0
2
4
6
8
10
12
x 10-4
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Example of comparison between measured and simulated spectra for phi = 0.8 at 1 mm above the visible flamezone
3500 3505 3510 3515
0
5
10
15
x 10-4
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
simulated spectra
measured spectra
simulated spectra
measured spectra
Example of comparison between measured and simulated spectra for phi = 1.6 at 1 mm above the visible flamezone
Absorption lines
Master of Science Thesis 43
LTH | Susan Lindecrantz
4.3 Temperature and Concentration simulations in the combustion chamber
With the knowledge from the flame measurements, the goal is to investigate
different methods to determine the temperature and the concentration of investigated
species just before combustion.
4.3.1 Implementation and simulation of engine spectra
During a cycle of the engine, the gas in the cylinder is exposed to temperature
and pressure variations before, during and after combustion. Fig. 4.10 shows the
pressure and the temperature changes in function of the crank angle degree (CAD).
The CAD is a unit to measure the pistons position when the engine is running. As a
reference point, when the piston is located at its highest point, top dead center, the
CAD is equal to zero. The pressure variations have been measured during the cycle
of the engine. The temperature variation has been simulated (based on the pressure
trace) and is therefore subject to a greater uncertainty.
Fig. 4.11 Shows the temperature and measured pressure changes in the engine.
-400 -300 -200 -100 0 100 200 300 4000
10
20
30
40
50
60
X: -9.25
Y: 35.05
CAD / degrees
Pressure / Bar
X: -37.35
Y: 10.07
X: -55.4
Y: 5.024
X: -94
Y: 2.01
-400 -300 -200 -100 0 100 200 300 400400
600
800
1000
1200
1400
1600
1800
X: -9.25
Y: 1008
CAD / degrees
Temperature / K
X: -37.35
Y: 780.2
X: -55.4
Y: 656.2
X: -94
Y: 527.9
44 Chapter 4 - Measurement and Simulations
Susan Lindecrantz | LTH
The temperature varies between about 400–1800 K and the pressure about
1-60 Bar. The ignition point can be identified in Fig. 4.11 on both the temperature
and the pressure plots, just before top dead center where the temperature and
pressure curves get much steeper. Four different points, before combustion have been
chosen for investigation; these points have been marked in Fig. 4.11. To find the
optimal point for measurements, these simulations were performed with temperatures
and pressures listed in table 5.
Table 5 Lists the possible measurements points for the engine experiment.
Measurement
points
CAD
[ Degrees ]
Pressure
[ Bar ]
Estimated
temperature [ K ]
P1 -9.25 35.05 1008
P2 -37.5 20.07 780
P3 -65.4 5.02 656
P4 -94.0 2.01 528
The simulation of the emission, created in the previous chapter, requires that
there is some first estimation of the mole fraction of CO2 in the combustion chamber,
to give an approximation of the half-widths of the lines and the partial number
density. This is mainly used for the optical depth simulation. For this purpose Eq.
(2.24) is used to estimate the mole fractions of H2O and CO2 at intake when the
engine is running on a lean fuel. From this equation the air-fuel-ratio of 1.2 gives a
mole fraction of 10.51% CO2 and 11.83% H2O after combustion and for air-fuel-
ratio of 1.6 gives a mole fraction of 8.00% CO2 and 9.00% H2O. It should be noticed
that these concentrations come from combustion and a large fraction is removed in
the exhaust stoke. Only a small fraction is remaining for the new cycle during intake
of new air and fuel. Despite this the concentration has been used as a first estimation.
For the simulations the air-fuel-ratio of 1.2 has been considered since the change
between the two is minimal with one being slightly bigger, see Fig. 4.12.
Master of Science Thesis 45
LTH | Susan Lindecrantz
Fig. 4.12 Shows the comparison between spectra simulated for CO2 with air-fuel-ratio of 1.2 and 1.6.
The first step in this investigation is to determine the optical depth and the
emission for the four measurement points in the engine chamber. Studying the
spectra of the flame gave a hint of what kind of species lay within the investigated
spectral regions of interest for CO2. A program was created, EngineOptical-
DepthAndEmissionSimulation.m, calculating the optical depth and the emission,
based on the previous program, using HITRAN for the three different spectral
regions of interest. With Eq. (2.22) the optical depth as a function of wavenumber,
can be calculated.
The first region is the fundamental band of CO2, located approximately
between the regions of 2250–2450 cm-1
and is the region of the chosen filter. The
second band is the combination band of CO2, located approximately between the
regions of 3450–3915 cm-1
. For this band there is interference from water lines even
at lower temperatures. For optical thick measurements this is not an issue, since the
blackbody is only dependent of the temperature of the investigated gas and not the
species. The third band for the second combination band of CO2, located
approximately between the regions of 4840–5100 cm-1
, is a weaker band of CO2 in
the infrared region and should therefore be a valid choice for concentration
measurement since it is not optically thick. For higher temperatures interference from
the water lines may arise in this region, especially above 5000 cm-1
. The pressure and
temperature is set to the points derived from Fig. 4.10 and listed in table 5. The path
length of the investigated gas column is 8.1cm. In the other case when the gas cloud
is not a true blackbody the emissivity in Eq. (4.3) is described by Eq. (2.12) and the
optical depth is determined with help of Eq. (2.22). To be able to estimate the
emissivity, an initial assumption of the mole fractions for CO2 and H2O of 10.51%
and 11.83% respectively, given from the global reaction formula have been used. It
should be noticed that if there is internal EGR, this relation might be slightly changed
according to Eq. (2.26). This program can be found in Appendix B.1.
2220 2221 2222 2223 2224 2225 2226 2227
0
0.5
1
1.5
2
2.5
3
x 10-6
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
10.51% CO2
9% CO2
46 Chapter 4 - Measurement and Simulations
Susan Lindecrantz | LTH
The next program, EngineTemperatureSimulations.m, is calculates the
temperature using the radiative transfer for optically thick case. For a true blackbody,
the intensity is only dependent on the temperature. Since this is not always the case,
the emissivity to the Planck function is also determined. Two filters for each spectral
region are used to transmit only the wavenumber within the regions that are to be
studied and block all other wavenumbers. By ratio measurement of the emission
between two bands, it is possible to get rid of the solid angle dependence of the
intensity for the setup. The idea is to use two optically thick bands to determine the
temperature. With no possibility of resolving the spectra from the engine are function
of wavelength, as obtained with a spectrometer, line-of-sight path-averaged
measurements are conducted with the infrared detector. The ratio between two
blackbody radiating bands, and a known emissivity, one obtains a function of
temperature,
∑
∑
∑∑
−−
−−==
1)/exp(
1
1)/exp(
1
)(
2
3
122
2
3
111
2
1
Tvcvcr
Tvcvcr
I
ITf
i
ibib
i
ibib
thickbi
thickbi
ε
ε (4.3)
Here r represents the spectral response of the setup and is set to one in these
simulations. ε is the emissivity of the gas in the engine for the spectral region, c1 and
c2 as the radiative constants and v is the wavenumber. The emissivity for a true
blackbody is equal to one. The initial assumption of 10.51% CO2 and 11.83% H2O
has been used here as well. Each emission band is multiplied with the filter’s
transmission curve for each region. The general idea is to investigate if the two bands
can be estimated as blackbody without the concentration dependence. This program
can be found in Appendix B.2.
Another possibility to determine the temperature is to use the transmission, and
thus the absorbance, to obtain the temperature for the combustion. One could use
H2O lines to obtain the temperature since they are more abundant and relatively free
from disturbances. The absorption coefficient depends on intensity of the line
strength component; therefore the temperature should be able to be estimated by
comparing the absorbance of different peaks for the same species. This method is
often called two-line technique. The Eq. (4.4) shows the absorbance at a specific
wavenumber, which is dependent on the absorption coefficient, the path length, the
total pressure and mole fraction of the investigated species. Dividing the absorbance
for two lines at specific wavenumber for the same species gives the relation stated
above, where the pressure, path length and mole fraction are cancelled out. Thus the
ratio of two absorption lines of the same species is a function of the temperature, see
Eq. (4.5). The temperature is determined using a tunable diode laser [35]. A line-pair
is scanned and its integrated intensity will give the temperature by taking the ratio of
the two lines.
LfvTSPxIIvTA vvspeciesvotv ),()/ln(),( =−= (4.4)
Master of Science Thesis 47
LTH | Susan Lindecrantz
(4.5)
S1(Tref, v1) and S2(Tref,v2) are given by Eq. (2.14) are the line strengths for the
line transitions 1 and 2 at a reference temperature Tref. The A(T,v1) and A(T,v2) is the
peak or integrated absorbance for each transition line. The selection of lines is based
upon that certain criteria must be fulfilled. The line should be free from interference
from other species; the absorption line should be strong enough to be registered by
the detector but small enough to avoid optical thickness. The transitions with large
lower state energies absorb at higher temperatures and not so much at lower
temperatures (room temperatures). Thus, for temperatures between 500-1000 K,
transitions with smaller lower state energies should be is considered. If one calculates
the integrated absorbance instead of the peak absorbance for the two-line method the
lines must also be accessed while scanning the diode laser; but, at the same time the
lines cannot be too close for overlapping at higher pressures. For this reason, this
method for integration at high pressures is not easily applicable since the broadening
of the lines makes it difficult to distinguish distinct lines. Another criterion is that the
lines should have well-separated lower state energies to obtain temperature
sensitivity. From reference [36] two line-pairs are selected for this investigation of
the temperature determination using this method, the H2O lines at 3982.06cm-1
and
3982.75cm-1
respectively 3966.77cm-1
and 3967.39cm-1
, see table 6. This simulation
can be found in CallTwoLineMethodAbsorptionTemperatureSimulation.m
where the absorbance ratio in Eq (4.5) is calculated is function of the temperature for
the given lines and their atomic parameters given in HITRAN. The program can be
found in appendix B.4.
Table 6 Shows candidate H2O line pairs for measurements of temperature and
water concentration near 2.5 µm based on HITRAN database [36].
Line
pair
Wavenumber
(cm-1
)
Wavelengh
(cm)
S@296 K
(cm-2
atm-1
)
E’’
(cm-1
)
∆E’’
(cm-1
)
Line
spacing
(cm-1
)
A 3982.06 2511.26 8.84x10-3
1581.33 2072.71 0.69
3982.75 2510.83 7.54x10-7
3654.04
B 3966.77 2520.94 4.61x10-5
2522.26 868.86 0.62
3967.39 2520.55 2.81x10-6
3391.12
With a known temperature, the concentrations can also be estimated from
emission using Eq. (4.3). For the temperature determination, the mole fraction of the
two major species H2O and CO2 is assumed to be known from the global reaction.
However, if there is internal EGR, these concentrations are changed according to Eq.
(2.26). A simulation was made to calculate the emission ratio between 3450–3915
cm-1
and 4840–5100 cm-1
. Since both H2O and CO2 exist in the band regions, an
−−−=
====∫∫
refref
ref
vspecies
vspecies
TTEE
k
hc
vTS
vTS
vTS
vTS
LdvfvTSPx
LdvfvTSPx
A
ATf
11)(exp
),(
),(
...),(
),(
),(
),()(
''
1
''
2
1
2
1
2
1
2
1
2
48 Chapter 4 - Measurement and Simulations
Susan Lindecrantz | LTH
assumption is made that for every mole of CO2, there is 1.2 times more H2O for
λ = 1.2, given from Eq. (2.24) . Each emission band is multiplied with the filter’s
transmission curve for each region. This simulation, EngineConcentration-
Simulation.m, can be found in Appendix B.3.
The next program, EngineConcentrationDiodeLaserSimulation.m, is
calculates the concentration of the investigated species using absorption
measurements with a known light source, such as a diode laser. The diode laser,
being monochromatic, makes it possible to only excite one wavelength and to avoid
interference from nearby lines that might come from other molecules. Some lasers
have the ability to tune the laser to desire wavelength, example of a tuning range is in
order of 1 cm-1
. The transmission is determined with Eq. (4.6) at the wavenumber of
the investigated spectral line and species of interest. The optical depth simulations
are used to determine the appropriate line in terms of interference of other species
such as H2O, absorbance and spacing between spectrallines. This program can be
found in Appendix B.6.
LfvTSPxt
ontransmissi
vvspecieseI
IT 0
),(
0
−−== (4.6)
In the next program, EngineConcentrationLEDSimulation.m, the same
investigation is made but with an LED light source. An LED’s line profile is much
wider, but it is a much cheaper option. The concentration can be obtained from a
modified version of the Beer-Lambert law, given by Eq. (4.6), in which the LED’s
line profile, Φ∆v, is used to calculate the transmittance for all wavenumbers i within
the LED’s band region. The center intensity of the LED’s profile is canceled out in
the ratio relation, thus one has a relation that is only dependent on the line profile of
the LED and the optical depth at each wavenumber within the LED band. The LED
line profile is multiplied with the filter’s transmission curve for the region. In the
measurement, the integrated intensity is measured and for this reason the modified
Beer’s law is summed with the band region of the LED. The modified relation is
given by Eq. (4.7). This program can be found in Appendix B.5.
∑∑
∑∑
∑∑
=
=
−
=
=
−
=
=
−
∆
−
====2
1
2
1
),(
2
1
2
1
2
1 0
2
1 0
0
0
v
vi i
v
vi
LfvTSPx
i
v
vi i
center
o
v
vi
L
i
center
o
v
vi
v
vi
L
v
t
ontransmissi
vvspeciesii e
I
eI
I
eI
I
IT
φ
φ
φ
φ κκ
(4.7)
4.3.2 Suggestion of experiment setup
The first step is to determine the temperature from optically thick thermal
emission measurement, directly from the gas within the cylinder of the engine while
it is running. The detector is timed with the engine cycle and registers the intensity
only when the engine comes to a pre-decided CAD value. Multiple measurements are
made to obtain an average. This data is then compared with the simulation of the
temperature, showing the band intensity ratio as a function of the temperature. The
simple illustration of the setup can be seen in Fig. 3.7c. The same setup can be used
to determine the concentration from emission measurement, as described above.
The next part is to estimate the concentration as a known temperature. Since
the temperature has not been experimentally determined, four different values were
chosen from pressure and temperature plots listed in table 5. Simulations of the
Master of Science Thesis 49
LTH | Susan Lindecrantz
optical depth for these values give, not only an idea of the optical depth, but also the
line positions of the different species. In the region of the second combination band,
only CO2 and H2O are of interest. With the experimentally determined temperature
and the given pressure, the concentration simulation provides a plot with the
transmission as a function of the concentration. The setup is displayed in Fig. 3.7a-b.
The light source intensity is measured before and after it enters the engine chamber.
The ratio between these two intensities gives the transmission.
4.3.3 Discussion of the engine simulations
The optical depth for three bands using HITRAN was evaluated for the three
different band regions of interest. The first one is the fundamental band of CO2,
located between the regions of 2250–2450 cm-1
, Fig. 4.13 displays the result. The
simulation showed that the fundamental band is optically thick for both the low
pressure and high pressures used for the simulation.
2250 2300 2350 2400 2450 25000
20
40
60
80
100
120
Wavenumber [ cm-1 ]
P = 2.01 Bar; T = 528 K
Optical depth [ - ]
2250 2300 2350 2400 2450 25000
10
20
30
40
50
60
70P = 5.02 Bar; T = 656 K
Wavenumber [ cm-1 ]
Optical depth [ - ]
2250 2300 2350 2400 2450 25000
20
40
60
80
100P = 20.07 Bar; T = 780 K
Optical depth [ - ]
Wavenumber [ cm-1 ]
2250 2300 2350 2400 2450 25000
10
20
30
40
50
60
70P = 35.05 Bar; T = 1008 K
Optical depth [ - ]
Wavenumber [ cm-1 ]
a)
50 Chapter 4 - Measurement and Simulations
Susan Lindecrantz | LTH
Fig. 4.13 Shows the optical depth a) and the corresponding emission simulations b) for the
fundamental band for the investigated points, P1-P4.
The fundamental band of the CO2 is clearly optically thick, especially at the
center of the band structure. This can also been seen in the emission plot for the same
band. In Fig. 4.13 b) the center of the band has merged to the Planck curve for all
investigated points. As a line becomes optically thick, the wing of the line grows and
at some point reaches the continuum, where it becomes a blackbody radiator. The
second band is the combination bands of CO2 and H2O, located approximately
between the regions of 3450 – 3915 cm-1
, Fig. 4.14 displays the result.
2250 2300 2350 2400 2450
0
0.5
1
1.5
2
2.5
x 10-5 P = 2.01 Bar; T = 528 K
Intensity [ a.u. ]
Wavenumber [ cm-1 ]
2250 2300 2350 2400 2450 2500
0
2
4
6
8
x 10-5 P = 5.02 Bar; T = 656 K
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
2250 2300 2350 2400 2450
0
0.5
1
1.5
2
2.5
3
3.5
x 10-4
Wavenumber [ cm-1 ]
Intensity [ cm-1 ]
P = 20.07 Bar; T = 780 K
2300 2350 2400 24500
1
2
3
4
5
x 10-4 P = 35.05 Bar; T = 1008 K
Intensity [ a.u. ]
Wavenumber [ cm-1 ]Planck curve simulated emission
3450 3500 3550 3600 3650 3700 3750 3800 3850 3900 39500
1
2
3
4
5P = 35.05 Bar; T = 1008 K
Wavenumber [ cm-1 ]
Optical depth [ - ]
3450 3500 3550 3600 3650 3700 3750 3800 3850 3900 39500
1
2
3
4
5
6P = 20.07 Bar; T = 780 K
Wavenumber [ cm-1 ]
Optical depth [ - ]
3450 3500 3550 3600 3650 3700 3750 3800 3850 3900 39500
1
2
3
4
5
6P = 5.02 Bar; T = 656 K
Wavenumber [ cm-1 ]
Optical depth [ - ]
3450 3500 3550 3600 3650 3700 3750 3800 3850 3900 39500
1
2
3
4
5
6
7P = 2.01 Bar; T = 528 K
Wavenumber [ cm-1 ]
Optical depth [ - ]
b)
a)
Master of Science Thesis 51
LTH | Susan Lindecrantz
Fig. 4.14 Shows the optical depth a) and the corresponding emission simulations b) for the
combination band around 3700 cm-1
for the investigated points, P1-P4.
The third band for the combination band of CO2, located approximately
between the region of 4840 – 5100 cm-1
, Fig. 4.15 displays the result. This is the
weakest among the chosen bands of CO2, in the infrared region for investigation and
should therefore be a candidate for optically thin measurements. The simulation
showed that the band is optically thin for all four measurement points. The emission
lines are well under the Planck function for all measurement points.
3500 3550 3600 3650 3700 3750 3800 3850 3900
0
1
2
3
4
x 10-6
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
P = 2.01 Bar; T = 528 K
3500 3550 3600 3650 3700 3750 3800 3850 3900
0
0.5
1
1.5
2
2.5
x 10-5 P = 5.02 Bar; T = 656 K
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
3500 3550 3600 3650 3700 3750 3800 3850 3900
0
2
4
6
8
x 10-5 P = 20.07 Bar; T = 780 K
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
3500 3550 3600 3650 3700 3750 3800 3850 3900
0.5
1
1.5
2
2.5
3
3.5
x 10-4
Wavenumber [ cm-1 ]Intensity [ a.u. ]
P = 35.05 Bar; T = 1008 K
simulated emission Planck function
b)
52 Chapter 4 - Measurement and Simulations
Susan Lindecrantz | LTH
Fig. 4.15 Shows the optical depth a) and the corresponding emission simulations b) for the
combination band around 4900 cm-1
for the investigated points, P1-P4. The Planck function is not
visible in figure.
Overall the line strength for CO2 decreases with increasing pressure as the lines
become wider, and it is more difficult to distinguish separate the line profiles. At
higher temperature, higher energy levels are populated and thus the molecular bands
expand to higher rotational and vibrational quantum numbers. This is seen as a
widening of the band structure.
The fundamental band is classified as optically thick for all considered
measurements points for the engine measurement. The simulation showed that the
fundamental band is optically thick for both the low pressure and high pressures used
4750 4800 4850 4900 4950 5000 50500
0.01
0.02
0.03
0.04
0.05
Wavenumber [ cm-1 ]
Optical Depth [ - ]
P = 2.01 Bar; T = 528 K
4750 4800 4850 4900 4950 5000 50500
0.01
0.02
0.03
0.04
0.05
0.06
0.07
Wavenumber [ cm-1 ]
Optical Depth [ - ]
P = 5.02 Bar; T = 656 K
4750 4800 4850 4900 4950 5000 50500
0.02
0.04
0.06
0.08
0.1
Optical Depth [ - ]
Wavenumber [ cm-1 ]
P = 20.07 Bar; T = 780 K
4750 4800 4850 4900 4950 5000 50500
0.02
0.04
0.06
0.08
0.1
0.12P = 35.05 Bar; T = 1008 K
Wavenumber [ cm-1 ]Optical Depth [ - ]
4750 4800 4850 4900 4950 5000 50500
1
2
3
4
5
6
7
8x 10
-9 P = 2.01 Bar; T = 528 K
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
4750 4800 4850 4900 4950 5000 50500
0.5
1
1.5
2x 10
-7 P = 5.02 Bar; T = 656 K
Intensity [ a.u. ]
Wavenumber [ cm-1 ]
4800 4850 4900 4950 5000
2
4
6
8
10
12
x 10-7 P = 20.07 Bar; T = 780 K
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
4750 4800 4850 4900 4950 5000 50500
0.2
0.4
0.6
0.8
1
1.2
1.4x 10
-5 P = 35.05 Bar; T = 1008 K
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
a)
b)
Master of Science Thesis 53
LTH | Susan Lindecrantz
for the simulation. The optical depth of the combination band at 3500 cm-1
is more
difficult to decide since the optical depth is less than one for the lines between the
stronger H2O lines and in the centerlines it never reaches the blackbody continuum in
the emission spectra. This is perhaps something to consider for the temperature
determination of a true blackbody radiator. For the CO2 the optical depth seems to be
more or less below one, indicating that for a pressure of 2 bars, in the band region, it
is not always optically thick. Only around 3750 cm-1
is the optical depth larger than
one for CO2 in the two limiting cases. For the combination band at 4900 cm-1
the
optical depth is clearly optically thin since it is below one and the emission spectra is
well under the blackbody curve.
The temperature can be estimated for optical thick bands accordingly to Eq.
4.3. The temperature simulation was conducted for the case of a true blackbody, and
the case where the emission is dependent on the blackbody times the emissivity for
the four measurements point’s pressures during the engine cycle before ignition, the
result are displayed in Fig. 4.16.
Fig. 4.16 Shows the temperature simulations for the four different points with pressures as constant
using HITRAN from table 5. Each plot displays also the band ratio for a true blackbody radiation
when the emissivity is equal to one.
For P4 and P3, at lower temperatures the ratio of the emission from the bands
does not act like the ratio between the bands of a true blackbody emitter. When the
pressure increases, for P2 and P1, the similarities are apparent for the lower
temperatures. In these simulations, the first combination band has been divided with
the fundamental band of CO2. The first combination band contains both the
possibility of emission from H2O and CO2. As seen in the flame measurements, H2O
lines grow with higher temperatures. It follows that, for lower temperatures, the
fundamental band is much stronger than the first combination band; thus, the
emission ratio is less sensitive to temperature. This deviation could be due to the first
combination band no longer being optically thick. However, as shown in previous
plots, as temperature and pressure grow, so that the first combination band (mostly
54 Chapter 4 - Measurement and Simulations
Susan Lindecrantz | LTH
due to H2O lines), and the fundamental band has merged to the continuum. This is
true at least for the lower temperature ranges. A certain decrease in the temperature
plot is noted for temperatures higher than 1000 K. This is probably due to the fact
that one or both bands are optically thin for the given conditions. Another reason
could be that HITRAN database is less accurate for these higher temperatures, and is
missing many of the hot bands that can be found in HITEMP95. For P1 the
HITEMP95 was used for temperature simulation, the result is displayed in Fig. 4.17.
The same simulation was made, but with lower concentrations to see if there was a
difference. The previous used concentration has been estimated from the products of
the global reaction formula and hence the concentration has been for a situation with
100% EGR to the next cycle. In reality most of the exhaust gas will have left the
chamber as the new cycle begins and only a small percentage is left behind in the
chamber as it is filled with new fuel and air. The result is also displayed in Fig. 4.17.
Fig. 4.17 Shows the temperature simulations for point 1 (P = 35.05 Bar and T = 1008K) using
HITEMP (purple curve). The same simulation was made with lower concentrations with 5% CO2 and
6% H2O (light blue curve).
The result was that at higher temperature, the curve simulated with HITEMP is
closer, however, still not equal to the ratio of the Planck curves. The HITEMP was
last updated in 1995 so some lines may be not accounted for. Another explanation for
this deviation is that the first combination band might not be optically thick for the
combination of high pressure and high temperatures. Further investigation showed
that the band was optically thin. It appears that the optical depth for the first
combination band is optically thin for P = 35.05 Bar and T = 1008K and might be the
reason the temperature simulations fail here. The same investigation was made for
lower concentrations of water and CO2; the figure showed less agreement to the ratio
of Planck curves. The explanation could be that the first combination is optically thin
at this pressure and temperature. In other words, not only the temperature, but also
the concentration has impact on the optical depth of the band for the same optical
path length.
Temperature determination by absorption method is also studied. A method
called the two-line method has been reported, that uses the absorbances of two lines
200 400 600 800 1000 1200 1400 1600 1800 20000
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Temperature [ K ]
Sum(Iv(3450-3915)/I v(2250-2450)) [ - ]
P1: P = 35.05 Bar
Planck function
Simulated curve - HITRAN - 10.51 % CO2 + 11.83 % H
2O
Simulated curve - HITEMP - 10.51 % CO2 + 11.83 % H
2O
Simulated curve - HITEMP - 5.0 % CO2 + 6.0 % H
2O
Master of Science Thesis 55
LTH | Susan Lindecrantz
of the same species. The temperature then becomes a function of the ratio between
the line strengths and temperature, see Fig. 4.18 and Fig. 4.19 for the result. Two
line-pairs where studied at 3982.06 cm-1
and 3982.75 cm-1
respectively 3966.77 cm-1
and 3967.39 cm-1
based on certain criteria for high temperature relations,
recommended by Farooq et. al. [36]. These lines were chosen for high temperature
measurements at atmospheric pressures, like combustion in a flame.
However, in the engine chamber the pressure variations are between 2-35 bars.
As the pressure increases so does the broadening of the line displayed in the two
figures. To obtain the integrated absorbance of the two lines with a tunable diode
laser the line profile has to be distinguishable, this proves to be difficult for higher
pressures. For this reason, the absorbance peaks are used here in Eq. (4.5) with the
assumption of the same line profiles for the lines. Fig. 4.19 shows a temperature
curve that is more sensitive to the absorbance ratio. It should be noticed that the
figures also can be used for integrated intensities. This could be because the lines
have lower energy difference than the lines in Fig. 4.18.
Fig. 4.18 Upper image shows the simulation of the ratio of the peak absorbance’s for two water lines
at 3982.06 cm-1
and 3982.75 cm-1
as function of temperature. The lower images show the two lines
influences of temperature and concentration. Image to the right has been rued with T = 528 K and the
image to the left with T = 1008 K.
400 600 800 1000 1200 1400 1600 1800 20000
0.1
0.2
0.3
0.4
0.5
Temperature [ K ]
f(T) = A(T,v2)/A(T,v1)
3980 3980.5 3981 3981.5 3982 3982.5 3983 3983.5 3984 3984.5 39850
0.2
0.4
0.6
0.8
1
1.2
1.4x 10
-4
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
T = 1008 K
3980 3980.5 3981 3981.5 3982 3982.5 3983 3983.5 3984 3984.5 39850
0.2
0.4
0.6
0.8
1x 10
-6
Wavenumber [ cm-11 ]
Intensity [ a.u. ]
T = 528 K
P = 35.05 Bar P = 20.07 Bar P = 5.02 Bar P = 2.01 Bar 3982.75 cm-1 3982.06 cm-1
56 Chapter 4 - Measurement and Simulations
Susan Lindecrantz | LTH
Fig. 4.19 The upper image shows the simulation of the ratio of the peak absorbance’s for two water
lines at 3966.77 cm-1
and 3967.39 cm-1
as function of temperature. The lower images show the two
lines influences of temperature and concentration. Image to the right has been rued with T = 528 K
and the image to the left with T = 1008 K.
The concentration simulation from the ratio of two emission bands with known
temperature can be found in Fig. 4.20. The results seem to implicate that the
concentration is more sensitive for the measurement points with lower temperatures,
in which the intensity between the two bands differs a lot. As the temperature
increases, the intensity for the first combination band seems to decrease to such
extent that the second combination band gets stronger in comparison. It should be
noted that these simulations assumes that the relation between the H2O and the CO2
stays the same, which might not be the case in the reality during the engine cycle.
Although the two band regions had been specially chosen to be ‘water free’, the first
combination band contains water lines. The trouble with emission measurement is
the interference of water lines for both bands for optically thin measurements. The
optimal case would be to investigate band regions that are free from H2O
interference.
400 600 800 1000 1200 1400 1600 1800 20000
0.5
1
1.5
2
2.5
Temperature [ K]
f(T) = A(T,v 2)/A(T,v1)
3964 3965 3966 3967 3968 3969 39700
1
2
3
4x 10
-7
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
3964 3965 3966 3967 3968 3969 39700
0.5
1
1.5x 10
-4
Intensity [ a.u. ]
P = 2.01 Bar P = 5.02 Bar P = 20.07 Bar 35.05 Bar 3966.77 cm-1 3967.39 cm-1
Master of Science Thesis 57
LTH | Susan Lindecrantz
Fig. 4.20 Shows the simulation of the ratio of band emission of CO2 as function of concentration.
The assumption of for every mole CO2 there exists 1.2 times more H2O. Each bandintensity is
multiplied with the filter transmission curve.
The optical depth plots were used to find possible line positions of CO2 that
were not compromised by strong water lines and could be used for concentration
measurement with a diode laser as a light source. The chosen line positions for this
investigation are displayed in table 5. The result of the simulation using these
wavenumbers is displayed in Fig. 4.21.
Table 7 Lists the possible measurements points for concentration measurement
using a laser diode at the same wavelength.
Measurement
points
Line position
[cm-1
]
Optical Depth
[ - ]
P1 4991.26 0.07035
P2 4991.25 0.0226
P3 4991.23 0.0188
P3 4945.10 0.01847
P4 4945.10 0.02165
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
5
10
15
20
25Concentration Simulation between Two Optical Thick Bands (combustion of lambda = 1.2)
Concentration / -
Sum(Iv(3450-3915)/I v(4752-5027)) [ a.u ]
P3: T = 656K; P = 5.02 Bar
P4: T = 528K; P = 2.01 Bar
P1: T = 1008K; P = 35.05 Bar
P2: T = 780K; P = 20.07 Bar
58 Chapter 4 - Measurement and Simulations
Susan Lindecrantz | LTH
Fig. 4.21 Shows the simulation of the absorbance in function of the mole fraction of CO2 when the
laser diode has been used as a light source for a T = 528K.
According to this simulation, the absorbance changes very little for small
concentration changes. For the lines investigated, only about 20% of the CO2 is
absorbed for a concentration of 100%. For about 10% CO2 there is about 2-4%
absorption. If it is possible to measure small absorbances in the engine setup, this
could be an alternative method since water interference should be minimal for the
diode laser due to its monochromatic feature.
The concentration simulation, using an LED as light source, can be found in
Fig. 4.22. All four points have been used, and is distinguished by different colors in
the figure. The LED line profile is very broad, to narrow it down a filter was
incorporated into the simulation, preventing unwanted water lines at higher
wavenumbers.
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
Concentration [ - ]
Absorbance [ - ]
Concentration simulation with an laser diode for different lines
P1 - 4991.26 cm-1
P2 - 4991.25 cm-1
P4 - 4945.10 cm-1
P4 - 4945.10 cm-1
P2 - 4991.23 cm-1
Master of Science Thesis 59
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Fig. 4.22 Shows the simulation of the absorbance in function of the mole fraction of the combined
CO2 and H2O when the LED has been used as a light source. The filter around 4840-4949 is used to
narrow the LED line profile.
The figure shows that the absorbance increases almost linearly with the
concentration for the LED. The absorbance is much stronger than for the laser diode
simulation. This is since the absorbances from all lines within the LED region (or
filter) contribute and is much stronger than the single lines. If this region is free from
water lines, this could be a method to determine the concentration of CO2.
The biggest difficulties are to find appropriate lines for the CO2 concentration
measurements without interference of H2O lines. As the pressure increases, so does
the broadening of the spectral lines and the lines get more smeared out? From Eq.
(4.4) the absorbance is linear to the mole fraction of the investigated species, this
relation is hinted at a previous absorption concentrations simulations. With known
concentration the EGR can be estimated with help of Eq. (2.27) and (2.28).
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
Concentration [ - ]
Absorbance [ - ]
Concentration simulation with an LED for the different measurement points
P1 - LED
P2 - LED
P3 - LED
P4 - LED
60 Chapter 5 – Conclusion and outlook
Susan Lindecrantz | LTH
Chapter 5 – Conclusion and outlook
5.1 Conclusion
In this investigation high resolution spectra of a premixed laminar burner for a
lean and a rich flame at different locations above the burner are studied. With help of
these spectra a simulation code for generating emission was created. The different
approaches were studied in order to obtain information about the temperature or
concentration from a gas in an engine just before combustion, with the aim of finding
ways to be able to estimate the internal EGR by the CO2 concentration.
From the CHEMKIN simulation, six species were chosen to be studied since
they are assumed to be the main contributors of the combustion of CH4 and C8H18.
From the flame investigation, it is clear that the HITRAN and HITEMP database
provides with important spectroscopic data for the infrared region. It has shown to be
easy to use and a good tool to for simulating spectra in MATLAB, in terms of line
identification and simulation, provided that there is no absorption from the
surrounding.
Absorption from air is a huge factor when measuring emission, since it absorbs
at the regions of interest; the fundamental band of CO2 and the first combination
band of H2O. To simulate the intensity it is essential to know the temperature and the
mole fractions of the investigated species. This creates a problem since the two are
often not known. In this study, an initial estimation of the mole fraction from the
reaction formulas was made to give an initial estimation in the engine simulations.
Different methods have been studied to extract this information with either emission
or absorption methods.
Using the emission from two optically thick bands to obtain the temperature has
proved to be dependent on the optical thickness of the first combination band, which
proved to be optically thick at the central line of most lines, and optically thin in the
wings. From the emission plots it is seen that the combination band never really
reaches the continuum at the center of the lines, but is very close. Despite this it
seems to be acting almost like a blackbody for high pressures in the temperature
simulation, where the ratio of emission of the two bands was very closes the other
curve using emissivity equal to one at lower temperatures.
At higher temperatures and thus higher pressures, this deviation increases,
probably due to the fact that HITRAN is less accurate above 1000K and that the first
combination band is less optically thick, especially for the water lines. When
HITEMP was used for higher temperatures, the band ratio increased but not enough
to agree with the curve of two blackbody curves. This is probably due to missing
lines in the HITEMP database, which last was updated in 1995, or due to the first
combination band being optically thin. It was shown that the concentration affects the
optical depth of the bands. For the concentration simulation, the following
assumption has been made, that for every mole of CO2 there is 1.2 times more H2O
given from the reaction formula of C8H18. This assumption is not ideal, especially if
the relation does not agree with the reality. For this reason, it would be desirable to
get rid of the concentration dependence in the emission by using blackbody
Master of Science Thesis 61
LTH | Susan Lindecrantz
measurements. Thus, with the knowledge of the concentration and temperature the
emissivity can be estimated and hence the emission.
Another method to investigate the temperature with absorbance, hence
transmittance, is to take the ratio of integrated absorbance from two lines. For the
same species this gives a relationship that is temperature dependent only. The line
used for this investigation was chosen from reference [36], which was aimed for
combustion of a flame in the range of 1000-2000K. If temperatures below this range
are considered, then lines with lower low energy states should be considered, since
they absorb at lower temperatures.
This method is attended to be used for the integrated absorbance instead of the
peak absorbance. The problem with integrated absorbance measurement is to find
lines that are easily distinguishable in the line profile, especially at higher pressures,
since the lines get broadened with increasing pressure. In the engine there is high
pressures, this method is then not optimal for the measurement points near the
combustion point. It might be possible to use this method for P4 and P3 since the
lines are less broadened, but in the same time, it was noticed that for the chosen lines
the intensity was weaker.
A simplified solution would be to consider the peak absorbance instead. With
the peak absorbance, the line profile at the center of the lines from the absorption
coefficient relation cannot be cancelled out. As the line profile changes with the
HWHM, even at the centerline, knowledge of the partial pressures due to the
Lorentzian broadening. However, in this investigation, Lorentzian is assumed to be
the same for both lines for simplification. Peak absorbances are easier to obtain
where there is rapid change in temperature and pressure as the engine goes thru its
cycle. It is not clear if it is possible to tune the laser fast enough to obtain the needed
information during one measurement at the given CAD position or to tune the laser
with every new cycle for obtaining the integrated intensity in sum of the cycles. The
integrated intensity would provide a better option, because no assumption is made,
and it is not dependent on the concentration to estimate the line profile as with the
peak absorbance. This is because the integrated line profile is normalized to be equal
to one for the whole line. In conclusion, this two line method works best for low
pressures and high temperature, something obtained in a flame but perhaps not in an
engine.
With the knowledge of the temperature, the concentration can be determined.
Using the Beer’s law for the peak transmission of two lines from the same species,
the concentration can be obtained. The line can’t be too weak in intensity, since it
gives less sensitivity, but it can’t be optically thick, since then the emission is only
dependent on the temperature. Two light sources were investigated, the LED and the
laser diode. The LED gave higher concentration sensitivity, since the absorbance for
each line within the LED line profile (or in this case; the filter) are added together.
Water lines might interfere here since these lines gets stronger with increasing
temperature and concentration. The chosen filters are used to narrow down the LED
region to a region with little interference of water lines. Even so, this is not a perfect
solution to minimize the interference from water. The downside is that the CO2 lines
are very weak in the second combination band region compared to the other stronger
combination bands. The CO2 is stronger around 5000 cm-1
but since the water
interference is too great in this region, the CO2 around 4881.8 cm-1
was chosen for
this study. The diode laser can be tuned into a region free of water lines; however, the
absorption changes very little with the concentrations since these lines are not great
62 Chapter 5 – Conclusion and outlook
Susan Lindecrantz | LTH
absorbers. The diode laser is a suitable choice since it is simple to use, provides in-
situ measurement and an optimal choice of line the light source provides with an
interference free measurement due to the monochromatic characteristic. On the other
hand, the LED is a much cheaper choice and simple to use. In this study the LED was
very broadband and it is difficult to avoid interferences from other species like water.
Accordingly, with Beer’s law, the summed effect can be obtained and thus the
concentration from the contributors.
5.2 Outlook
In this initial investigation certain assumptions have been made. The scattering
effect is assumed to be negligible. In further investigation, the scattering effect
should be more closely investigated, especially if there are particles in the system.
Then the radiative transfer becomes dependent on the extinction from absorption and
scattering, see Eq. (2.6).
To determine the temperature from emission measurement, an estimation of the
concentration from the reaction formulas has been used for optically thin emission.
The optimal case would be to find another band that is optically thick like the
fundamental band of CO2. Then the ratio of emission can be expressed as a function
of temperature and wavenumber and not the concentration. For temperature
determination with the two-line method, a further investigation of lines fitting the
preferences of the combustion engine situation can be made. The lines chosen in this
investigation were optimal for low pressure and high temperature measurement. It
might be possible to obtain a line of CO2 or H2O that is well-defined for relatively
high pressure (but still not too wide to be undistinguishable from the neighboring
lines) and high temperature for integrating absorbance measurement. If the HWHM
is known for the line peak, absorbance’s can be used instead of the integrated
absorbances.
Instead of using CO2 concentration to estimate the EGR, the water lines in the
second combination band are a possible alternative for the diode laser simulation,
since it might give higher absorbance sensitivity for the concentration determinations
and is not as sensitive of CO2 interference since its dominant feature for higher
temperatures in the region.
Another assumption would be that if the temperature and the air-to-fuel ratio
are known, the EGR can be determined indirectly using (2.26) in which the
concentration is obtained from the reaction formula. Then the emission ratio can be
calculated as function of the EGR and compared with measurement. Another way
would to use the new concentration at certain assumption of EGR to fit the scanned
absorbance spectra of a diode laser with the simulated spectra.
For the emission measurement, air absorption can be avoided by using fibers
between the window of the engine chamber and the detector. For the engine
measurement, one might have to consider the radiative emission from the walls of the
combustion chamber and the spark plug. The emission from the heated walls and
spark plug might also be captured by the detector and be a source of error. If it is
large enough, compared to the spectral features of interest, it needs either to be
subtracted or accounted for in the simulation. If it’s small enough, it can be
neglected. The temperature of the walls in the engine should be much lower than the
Master of Science Thesis 63
LTH | Susan Lindecrantz
actual gas inside the chamber. If that is the case then the wall should give rise to a
lower blackbody radiation curve contribution. However since this engine has two
opposite windows this effect can be assumed to be reliable. The spark plug has been
blocked in the line-of-sight measurement. Due to this these contributions have been
assumed in this initial study to be insignificant.
If the emission spectra could be obtained from a FTIR spectrometer, emission
simulations could be made to obtain a best fit of the simulated and measured spectra.
By study of these spectra, the information about the temperature and then the
concentration can be made. The next step would then be to use the emission ratio of
two single lines of the same species to obtain the concentration. As stated before the
emission depends linearly on the concentration for optically thin lines, hence the Eq.
(2.10) which simplifies to the Planck function times the optical depth.
Using a FTIR spectrometer might prove to be difficult if one want to obtain
high resolution spectra since it takes time of scanning the movable mirror if high
resolution is desired. This is a problem if you are to measure the intensity at a certain
CAD position since there is not time for the FTIR spectrometer to complete its
measurement as the engine is running.
With the upcoming new release of the HITEMP database, more precise and
extended simulations can be made for high temperature spectra. The next step could
be to create a program which can simulate the emission, the optical depth and hence
the transmission and absorbance with a simple click. This could be very useful for
students and researchers alike.
Experiments to test the possibility of determining the temperature and the
concentration from the simulations were not conducted in this work, but can be
considered for future investigations.
64 Acknowledgement
Susan Lindecrantz | LTH
Acknowledgement
The author wishes to thank the division of Combustion Physics at Lund
University, Faculty of Engineering for giving me the opportunity to perform this
master thesis. I also would like to thank my two supervisors, Zhongshan Li and
Mattias Richter for taking their time to answer my questions. Also many thanks to
Sven-Göran Pettersson for his kind help.
Secondly I would like to thank my mother for always standing beside me and
encouraging me to go on. I would also like to thank my little Star for always cheering
me up when I most needed it.
Further I am very grateful to the division of Astronomy and Astrophysics for
letting us use their excellent FTIR spectrometer for the flame measurement, and for
the kind help from Hampus Nilsson and Henrik Hartman.
Finally many thanks to Dainis Dravins, Larry Rothman, Mark Linne, Bo Li,
Sun Zhiwei for helping me with my questions.
Master of Science Thesis 65
LTH | Susan Lindecrantz
Bibliography
[1]
Bood, Joakim (2009), Introduction to combustion, Lecture material in Laser-based
combustion diagnostics.
[2] Aldén, Marcus (1999), Laser spectroscopic techniques for combustion diagnostics,
Combust. Sci. and Tech., 1999, Vol. 149, pp 1-18.
[3] Pettersson, Anders (2004), Investigation of infrared chemiluminescence emission from
laboratory flames, Master of Science Thesis LTH, Division of Combustion, Lund
University, p 7.
[4] Svanberg, S. (2003), Introduction, Atomic and molecular spectroscopy – Basic Aspects
and Partial Application, Springer, pp 1: 5-65 : 55-60 : 57-58.
[5] Modest, Michael (2003), Radiative heat transfer, Academic press – an imprint of
Elsevier Science, p. 289.
[6] Colin, N. et. al, (1994), ‘Fundamentals of molecular spectroscopy’, 4th
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Hill.
[7] Absorption Spectrum, Wikipedia - the free encyclopedia, (2010-03-02),
http://en.wikipedia.org/wiki/Absorption_spectrum
[8] Thorne A., Liztén U., Johansson S. (1999) Spectrophysics – Principles and Applications,
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[9] Uncertainty Principle, Wikipedia - the free encyclopedia (2009-11-04)
http://en.wikipedia.org/wiki/Uncertainty_principle
[10] Linne, Mark (2002), Spectroscopic Measurement – An Introduction to the Fundamentals,
Academic Press, pp. 300-302: 36: 38-42: 63: 63: 63: 64: 66.
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[12] Radiative transfer, (2010-04-15), Wikipedia - the free encyclopedia,
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[13] Department of Chemistry – The University of Adelaide, (2010-03-04),
www.chemistry.adelaide.edu.au/external/socrel/content/beerslaw.htm
[14] Rothman, LS. et. al. (2006) J. Quant. Spectrosc. Radiat. Transfer Vol. 60, No. 5 - The
HITRAN Molecular Spectroscopic Database and Hawks (HITRAN atmospheric work-
station) 1996 edition, Elsevier Science Ltd, p 710.
[15] Rothman LS. et. al., (2010), HITEMP, the high-temperature molecular spectroscopic
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[16] Rothman, LS. et. al. (2009,) Journal of Quantitative Spectroscopy & Radiative Transfer
110, pp 533–572, Elsevier Science Ltd.
[17] Rothman LS. et. al., (1996), J. Quant. Spectrosc. Radiat. Transfer Vol. 60, No. 5, pp 665-
710, Elsevier Science Ltd.
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[18] Gharavi M. and Buckley SG. ((2004)), Single Diode Laser Sensor for Wide-Range H2O
Temperature Measurements, Applied spectroscopy, p 469.
[19] Combustion, Wikipedia - the free encyclopedia, (2009-11-05)
http://en.wikipedia.org/wiki/Combustion.
[20] Griffiths JF., Barnard JA. (1995), Flame and Combustion, Blackie Academic and
professional – An imprint of Chapman & Hall, pp 33 (Fig. 3.3): 32-33.
[21] Flames and flame structure (2009-12-03),
http://eyrie.shef.ac.uk./will/eee/cpe630/comfun3.html.
[22] Chiang, CJ., Stefanopoulou, AG. (2006), Sensitivity Analysis of Combustion Timing and
Duration of Homogeneous Compression Igniting (HCCI) Engines, Proceedings of the
2006 American Control Conference.
[23] Stone, Richard (1995), Introduction to internal combustion engines – second edition,
Society of Automotive Engineers, pp 1, 65.
[24] Internal combustion engine, Wikipedia - the free encyclopedia, (2010-01-25)
http://en.wikipedia.org/wiki/Internal_Combustion_Engine.
[25] Four stoke, Wikipedia - the free encyclopedia, (2010-02-16)
http://en.wikipedia.org/wiki/Four-stroke.
[26] Wirtz, Andreas (2008), Measurement of various exhaust gas components using
broadband absorption spectroscopy with a UV_LED light source, Bachelor thesis,
Division of Combustion, Lund University.
[27] Laser Technic website, (2009-09-17) Mid-infrared LED,
http://www.roithnerlaser.com/All_Datasheets/MID_IR/Led_20.pdf.
[28] Laser Technic website, (2009-11-24) Mid-infrared LED,
http://www.roithner-laser.com/Id_mid-ir.htm.
[29] How to choose an IR Detector, (2010-03-23)
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[30] Teledyne, Judson technologies, (2010-03-23)
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[32] Whiting, E. (1968), Quant. Spectrosc. Radiat. Transfer 8, p 1379.
[33] Liu, Yuyan et. al., (2001), Simple empirical analytical approximation to the Voigt profile,
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[34] Raytracing program written by Sven-Göran Pettersson.
[35] Zhou, X. et. al. (2005), Development of a fast temperature sensor for combustion gases
using a single tunable diode laser, Appl. Phys. B 82, pp 711-722.
[36] Farooq, A. et. al. (2008), In situ combustion measurements of H2O and temperature near
2.5µm using tunable diode laser absorption, IOP publishing, Mesa Sci. Technol. 19, pp
1-11.
Master of Science Thesis 67
LTH | Susan Lindecrantz
List of figures
Fig. 2.1 Illustrating the molecular energy structure, showing the electronic, vibrational
and rotational energy levels. The size of the energy difference between two
electronic states is around a few eV, two vibrational states a few 0.1 eV and
two rotational states a few 0.001 eV.
Fig. 2.2 Illustrating the three possible radiative processes for a two-level atom or molecule;
a) emission, b) absorption and c) stimulated emission.
Fig. 2.3 Shows comparison of three line profiles with the normalized intensity and the same
width.
Fig. 2.4 Illustration of the optical system for radiative transfer.
Fig. 2.5 Displaying the different zones in one dimensional premixed adiabatic flame along
with the concentrations and temperature profiles of the flame.
Fig. 2.6 Illustrating the four stroke engine cycle presented in the text.
Fig. 3.1 The experimental setup for the Fourier Transform Infrared Spectroscopy of the
flame.
Fig. 3.2 The premixed laminar burner with a flame stabilizer on top and a tube ventilation
system which carries most of the burned gases outdoors. The red spot is the laser
beam used for alignment into the spectrometer.
Fig. 3.3 Image showing the design of the slit used in the FTIR Spectrometer experiment
with a minimum aperture of 2 mm.
Fig. 3.4 The figure shows principle of the Michelson interferometer.
Fig. 3.5 The figure show the Fourier Transform Infrared Spectrometer used in the
experiment from the Atomic Astrophysics department in Lund University.
Fig. 3.6 The figure show layout of the spectrometer used in the experiment.
Fig. 3.7 A very simple illustration of the three possible measurements setup with the engine.
Image a) represents the absorption measurement using and diode laser and b) using
an LED with the same setup. Image c) represents the thermal emission
measurement.
Fig. 3.8 The figure shows the typical line profile at different temperatures for the LED
investigated.
Fig. 3.9 The figure illustrates the three filters transmittance profile. Figure a) displays an
transmittance curve around 3600-3800 cm-1
, b) an transmittance curve around
4840-4949 cm-1
and c) an transmittance curve around 2300-2450 cm-1
.
Fig. 3.10 The figure illustrates the engine considered for this project. A paper tube has been
placed between a collimator and the engine opening to minimize light interference
from the room. A filter has been placed in front of the detector to only detect light
at a certain wavelength band.
68 List of figures
Susan Lindecrantz | LTH
Fig. 3.11 The figure shows the sensitivities of the different types of detector materials in
functions of wavelength.
Fig. 4.1 Shows the setup for the flame measurement.
Fig. 4.2 Illustrates the visible flame zone during measurements which the positions of the
measurements locations was derived from.
Fig. 4.3 Shows the measured spectra, fitted curve of the measured spectra and the
calculated blackbody spectra for T = 1473.15 K. The calculated Planck function
was corrected to fit the measured curve with an arbitrary value.
Fig. 4.4 Displaying the effect of the sensitivity drop-off from the detector on the blackbody
spectra from Fig. 4.3 (zoomed).
Fig 4.5 Shows the resulting response function from Eq. (4.1).
Fig. 4.6 Shows the comparison between the different measured locations of the flame
spectra with φ = 0.8 and φ = 1.6.
Fig. 4.7 Shows the comparison between the flame spectra for 1 mm and 3 mm below
the visible flame zone for φ = 0.8 and φ = 1.6
Fig. 4.8 Shows an example of a study of the investigated species locations for the
flame with φ = 1.6.
Fig. 4.9 Shows the two examples of features in comparison between the flame spectra
for 1 mm above the visible flame zone for φ = 0.8 and φ = 1.6. The upper
image shows the band head of the fundamental CO2 (to the right) and the CO2
absorption lines (to the left). The lower image shows part of the combination
band of H2O.
Fig. 4.10 Shows the two examples of features in comparison between the flame spectra
for 1 mm above the visible flame zone for φ = 0.8 and φ = 1.6. The upper
image shows the combination band of H2O in which some lines have been
absorbed. The lower image shows part of the combination band of H2O.
Fig. 4.11 Shows the temperature and measured pressure changes in the engine.
Fig. 4.12 Shows the comparison between spectra simulated for CO2 with air-fuel-ratio
of 1.2 and 1.6.
Fig. 4.13 Shows the optical depth a) and the corresponding emission simulations b) for
the fundamental band for the investigated points, P1-P4.
Fig. 4.14 Shows the optical depth a) and the corresponding emission simulations b) for
the combination band around 3700 cm-1
for the investigated points, P1-P4.
Fig. 4.15 Shows the optical depth a) and the corresponding emission simulations b) for
the combination band around 4900 cm-1
for the investigated points, P1-P4.
The Planck function is not visible in figure.
Fig. 4.16 Shows the temperature simulations for the four different points with pressures
as constant using HITRAN from table 5. Each plot displays also the band ratio
for a true blackbody radiation when the emissivity is equal to one.
Master of Science Thesis 69
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Fig. 4.17 Shows the temperature simulations for point 1 (P = 35.05 Bar and T = 1008K)
using HITEMP. The first plot displays the temperature simulation. The second
and third plot shows the emissivity and the filter used for each band region,
the fundamental (band 1) and the first combination band (band 2). The filter
plot shows the filter for band 2.
Fig. 4.18 The upper image shows the simulation of the ratio of the peak absorbances for
two water lines at 3982.06 cm-1
and 3982.75 cm-1
as function of temperature.
The lower images show the two lines influences of temperature and
concentration.
Fig. 4.19 The upper image shows the simulation of the ratio of the peak absorbances for
two water lines at 3966.77 cm-1
and 3967.39 cm-1
as function of temperature.
The lower images show the two lines influences of temperature and
concentration. Image to the right has been runed with T = 528 K and the
image to the left with T = 1008 K.
Fig. 4.20 Shows the simulation of concentration of CO2 as function of temperature. The
assumption of for every mole CO2 there exists 1.2 times more H2O. Each
intensity of the band is multiplied with the filter transmission curve.
Fig. 4.21 Shows the simulation of the absorbance in function of the mole fraction of
CO2 when the laser diode has been used as a light source for a T = 528K.
Fig. 4.22 Shows the simulation of the absorbance in function of the mole fraction of the
combined CO2 and H2O when the LED has been used as a light source. The
filter around 4840-4949 is used to narrow the LED line profile.
70 List of tables
Susan Lindecrantz | LTH
List of tables
Table 1 Illustrates the uncertainties of the HITRAN database.
Table 2 Contains the spectroscopic parameters and units used in HITRAN
2004 and 2008.
Table 3 The gas mixture of the flame with their respective gas flows.
Table 4 Illustrates the calculated mole fractions and temperatures for the
respective investigated species versus the flame coordinates using
CHEMKIN.
Table 5 Lists the possible measurements points for the engine experiment.
Table 6 Shows candidate H2O line pairs for measurements of temperature
and water concentration near 2.5 µm based on HITRAN database.
Table 7 Lists the possible measurements points for concentration
measurement using a laser diode at the same wavelength.
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Appendix A: Code for flame investigation
A.1 CallProcessFTIRSpectraFunc
Example of code processing the measured spectra data in
MATLAB for one measurement point
function [plotWavenumber,measuredSpectra]= CallProcessFTIRSpectraFunc
% disp('. ')
% disp('. This program has been created by Susan Lindecrantz ')
% disp('. Contact: [email protected] ') % disp('. Master Thesis 2009/2010 ')
% disp('. ')
% Program: CallProcessFTIRSpectraFunc m
% last modified: 12-05-02
% 2009/2010 (c) Susan Lindecrantz, % Lund University - Faculty of Engineering
% About: % ---------------------------------------------------------------------
% Determines the ‘true’ spectra from the measurement. The function
% calculates and plot the Planck curve and use it to determine the % true spectra from the FTIR data measured by the spectrometer by
% eliminating the instrumental response function. The rows used in the files
% is already set below, cannot be set by values called with the func. %
% Note:
% This is an example for point at reaction zone, phi = 1.6 %
% Variables:
% --------------------------------------------------------------------- % measuredSpectra – measured spectra without the response of the setup
% RawDataFile – file containing the vector Data [ .DPT ] or [ .txt ]
% Data = [ plotWavenumber intensity ] – vector containing % plotWavenumber [ cm-1 ] measured wavenumber region from flame
% intensity [ a.u. ] measured intensity from flame
% Temp – temperature in [ K ] % FittedMesuredBBFile – file containing the fitted data from the vector BBData
% BBData = [ wavenumber BBintensity ] – vector containing
% BBintensity [ a.u. ] fitted measured blackbody intensity % wavenumber [cm-1] fitted measured blackbody wavenumber region
% FittedMesuredBBFile – file containing the fitted data from the vector BBData
% BBrowmax – maximum value of the row position for max wavenumber in % FittedMeasuredBBFile; set here to BBrowmax = 96 for fittedBB_expanded.txt
% BBrowmin – minimum value for the row position for min wavenumber in
% FittedMeasuredBBFile; set here to BBrowmax = 1 for fittedBB_expanded.txt % BBcolmax – maximum value of the col position for max wavenumber in
% FittedMeasuredBBFile; set here to BBrowmax = 2 for fittedBB_expanded.txt
% BBcolmin – minimum value for the col position for min wavenumber in % FittedMeasuredBBFile; set here to BBrowmax = 1 for fittedBB_expanded.txt
% MesuredBBFile – file containing the measured BB data, vector MBBData
% MBBData = [plotWavenumber measuredInt ] % rowmax – maximum value of the row position for max wavenumber in
% FittedMeasuredBBFile and RawDataFile; set here to
% rowmax = 398245 for the .DAT files from measurement (for the region) % rowmin – minimum value for the row position for min wavenumber in
% FittedMeasuredBBFile and RawDataFile; set here to
% rowmax = 99562 for the .DAT files from measurement (for the region) % colmax – maximum value of the col position for max wavenumber in
% FittedMeasuredBBFile and RawDataFile; set here to % rowmax = 2 for the .DAT files from measurement (for the region)
% colmin – minimum value for the col position for min wavenumber in
% FittedMeasuredBBFile and RawDataFile; set here to % rowmax = 1 for the .DAT files from measurement (for the region)
% PlanckCurve – calculated Planck curve for temperature Temp
% responseFTIR – the response functions curve % ---------------------------------------------------------------------
72 Appendix A: Code for flame investigation
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Temp = 1475.15;
PlanckNormValue = 190;
% =/\= Uploading the measured BB curve into vector MBBData
% =/\= Enter filename, row and column positions of the investigated region of the BB data.
MRawDataBB = load('Burner09042812.DPT');
MBBData = MRawDataBB(99562:398245,1:2);
% = /\= Uploading the fitted measured BB curve into vector BBData
% =/\= Enter filename, row and column positions of the investigated region.
RawDataBB = load('fittedBB_expanded.txt');
BBData = RawDataBB(1:96,1:2);
% =/\= Setting the wavelength region into vector plotWavenumber plotWavenumber = MBBData(:,1);
% =/\= Interpolate the fitted measured BB curve so it covers the whole region of plotWavenumber.
BBintensity = interp1(BBData(:,1),BBData(:,2),plotWavenumber,'linear');
% =/\= Uploading the RawDataFile into vectors Data
% =/\= Enter filename, row and column positions of the investigated region. RawData = load('Burner0904282.DPT');
Data = RawData(99562:398245,1:2);
% =/\= Calculating Planck curve for temperature
fradiationconst = 1.191062e-12; % First Radiation Constant [W cm^2 /sr]
sradiationconst = 1.438786; % Second Radiation Constant [K cm]
PlanckCurve = Planck_func(plotWavenumber,Temp);
% =/\= Calculating the true ‘spectra’ curve, using equations (4.1) and (4.2) in report.
% =/\= Calculating the Response function – Eq. (4.1)
ResponseFTIR = (BBintensity./PlanckCurve);
% =/\= Calculates the the ‘true’ spectra curve without response curve
measuredSpectra = (Data(:,2)./ResponseFTIR);
function [LPlanck] = Planck_func(v,T)
% =/\= Constants fradiationconst = 1.191062e-12; % [W cm^2 /sr]
sradiationconst = 1.438786; % [K cm]
% =/\= The Calculation of Planck's function
dominator = fradiationconst*(v.^3); expvalues = (sradiationconst/T).*v;
nominator = exp(expvalues)-1;
LPlanck = dominator./nominator;
% end of Planck_func func
end
% end of CallProcessFTIRSpectra func
end
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A.2 CallOpticalDepthFunc
Example of code for calling the function CallOpticalDepthFunc for calculating optical
depth in MATLAB
function [tauSpectra]=CallOpticalDepthFunc(v0, v, HWHM_L, SInt0, Temp, Elow, QTfunc,...
QTfunc_ref, ISOVALUE, ISONR, p, ps,opticallength)
% disp('. ')
% disp('. This program has been created by Susan Lindecrantz ') % disp('. Contact: [email protected] ')
% disp('. Master Thesis 2009/2010 ')
% disp('. ') %
% Program: CallOpticalDepthFunc m
% last modified: 12-05-02 % 2009/2010 (c) Susan Lindecrantz,
% Lund University - Faculty of Engineering
% % About:
% ---------------------------------------------------------------------
% Caculates the optical depth of the spectra called with the function. % The definition of optical thick gas is tau >> 1 and for optical thin gas, tau <= 1
% The function can only calculate the optical depth spectra for one species at the time.
% The data from the HITRAN file [.txt] must have been upoaded in previous code % before one calls this func.
%
% Variables: % ---------------------------------------------------------------------
% tauSpectra – the optical depth of the spectra
% v [ cm-1 ] – vector containing the region of the spectral range under investigation % v0 [ cm-1 ] – vectr containing the center wavenumber of the spectral lines with range of vector v
% Temp – temperature in [ K ]
% HWHM_L [ cm-1 ] – The Lorienztain half-with at half-maximum of the spectral line % Elow [ cm-1 ] – Lower energy level of the two level atom/molecule
% QTfunc [-] – The total partition function value for the molecule and isoptope for Temp % QTfunc_ref [-] – The total partition function value for the molecule and isoptope at
% reference temperature of 296K.
% ISOVALUE – The isotopic value for the molecule accordingly to HITRAN % ISONR – The isotopic number according the numbering system of HITRAN
% p [ atm ] – total pressure
% ps [ atm ] – partial pressure for the species investigated % opticalpath length [ cm ] – the optical path length estimated for gas column investigated.
% ---------------------------------------------------------------------
% Constants NL = 2.68676e19; % [ molecules cm^-3 atm^-1] Lochsmidths' number
% Definition of empty vectors tauSpectra = zeros(length(v),1);
count = 0;
% =/\= Calculating the absorption coefficient =/\=
% For Each Spectral Line the optical depth is calculated for the whole line for line = 1:length(v0)
% Get values of the partition functions and abundance QT = QTfunc(ISONR(line));
QTref = QTfunc_ref(ISONR(line));
% Transform the SInt (cm/molecules) to SInt (cm^-2 atm^-1) SInt = SInt0(line)*NL*(296/Temp);
% Obtaining the temperature corrected line intensity
% Unit (cm^-2 atm^-1) [ SIntT ] = SintensityTempConversion(SInt,Temp,Elow(line),...
QT,QTref,v0(line));
% Sets the Lorentzian Line profile [ line profile ] = Lorentzian( v0(line), v, HWHM_L(line) );
% Calculate the optical depth line for wavenumber(i)
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tauspectraline = SIntT*line profile*opticallength*ps;
% Summing overlapping lines to the total optical depth of the spectra tauSpectra = tauSpectra + (tauspectraline)';
% Printing out calculation progress as its being runned!
steps = round(length(v0)*0.05);
if count == steps
percent = (line)/(length(v0))*100;
D = ['--> Processing Optical Depth... ',num2str(fix(percent)),'%']; disp(D)
count = 0;
else count = count +1;
% end if
end
% end for
end
function [ SIntT ] = SintensityTempConversion(SInt0,T,lowE,...
QT,QTref,v0)
% =/\= Constants =/\=
fradiationconst = 1.191062e-12; % [W cm^2 /sr]
sradiationconst = 1.438786; % [K cm]
% =/\= Calculating the Temp Conversion =/\= SIntT = SInt0*((297*QTref*exp(-sradiationconst*lowE/T)*...
(1-exp(-sradiationconst*v0/T)))/...
(T*QT*exp(-sradiationconst*lowE/296)*... (1-exp(-sradiationconst*v0/296))));
% end of SintensityTempConversion func
end
function [ line profile ] = Lorentzian( v0, v, HWHM )
% =/\= Determine the line profile =/\= line profile = (((1/pi)*HWHM)./(HWHM^2 + ((v-v0).^2) ));
% end of Lorentzian func
end
% end of optical depth function
end
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A.3 CallEmissionFunc
Example of code calling the function CallEmissionFunc for emission simulation in MATLAB
function [plotWavenumber, emissionSpectra, emittanceSpectra, tauSpectra]=...
CallEmissionFunc(minWaveNr, maxWaveNr, resolution,Temp, p, ps,...
opticallength, hiType,RawDataFile, parasumFile, colmin, colmax, ISOVALUE)
% disp('. ')
% disp('. This simulation has been created by Susan Lindecrantz ') % disp('. Contact: [email protected] ')
% disp('. Master Thesis 2009/2010 ')
% disp('. ')
% Program: CallEmissionFunc m
% last modified: 12-05-02 % 2009/2010 (c) Susan Lindecrantz,
% Lund University - Faculty of Engineering
% About:
% ---------------------------------------------------------------------
% Calculating the emission, the emittance and the optical depth spectra for the investigated region % and species. The emission here is not dependent on the gas to be either optical thick or thin.
% Assumes the medium is 'hot' (i.e. emission is strong) and No external light source + neglecting
% line-of-sight absorption and scattering. % Assuming homogenity, line-of-sight measurement.
% Note! Function uploadHITRAN needs to be edited for CH4 where uploads fails for the current.
% Variables: % ---------------------------------------------------------------------
% emissionSpectra – the result; simulated emission spectra for the investigated region
% emittanceSpectra – the result; the emittance spectra for the investigated region % tauSpectra – the result; optical depth spectra for the investigated region
% plotWavenumber [ cm-1 ] – the investigated region % maxWaveNr – maximum value of the investigated region
% minWaveNr – minimum value of the investigated region
% resolution – resolution of the investigated region % Temp – temperature in [ K ]
% wavenumber [ cm-1 ] – a vector containing the wavenumbers of the uploaded spectral lines
% wavenumbershift [ cm-1 ] – a vector containing the shifted wavenumbers due to air-broadening % ISOVALUE – A vector of all isotopic values for the molecule accordingly to HITRAN
% ISONR – A vector for the uploaded isotopic number according the numbering system of HITRAN for vector wavenumber
% S0Intensity [cm-2 atm-1] – vector of the uploaded line strengths at 296K. % AirHWHM [ cm-1] – vector of the uploaded air-broadening for each line at 296K
% SelfHWHM [ cm-1] - vector of the uploaded self-broadening for each line at 296K
% Elow [ cm-1] – vector of the uploaded lower energy state of the spectral lines. % nT – temperature dependent exponent of AirHWHM.
% deltaP – air-pressure induced shift.
% p [ atm ] – total pressure % ps [ atm ] – partial pressure for the species investigated, ps = x*p where x is the species mole fraction.
% opticalpath length [ cm ] – the optical path length estimated for gas column investigated.
% RawDataFile [ .txt ] – file containing the vector of data from HITRAN or HITEMP generated by JavaHAWK. % parasumFile [ .txt ]– file containing the partition function values as function of temperature, values given in HITRAN’s
% ‘parasum.dat’ file. This file needs to be downloaded and first row removed to be able to be processed.
% colmax – maximum value of the col position in parasumFile % colmin – minimum value for the col position in parasumFile
% hiTYPE - can obtain values ‘HITRAN’ or ‘HITEMP95’ depending
% on what kind of file is uploaded. New HITEMP2010 is in the same format as HITRAN. % Note! Sometimes HITEMP95 don’t work – something with g-values.
% Partialfunc_ref – Partition func values at 296K
% Partialfunc – Partition func values at Temp % ---------------------------------------------------------------------
% =/\= Setting the wavenumber region for the bands
plotWavenumber = minWaveNr:resolution:maxWaveNr;
if strcmp(hiType,'HITRAN')
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% =/\= Uploading HITRAN data [ISONR,wavenumber,S0Intensity, AirHWHM,SelfHWHM,...
Elow, nT,deltaP] = uploadHITRAN (RawDataFile);
elseif strcmp(hiType,'HITEMP95')
% =/\= Uploading HITEMP data
[ISONR,wavenumber,S0Intensity, AirHWHM,SelfHWHM,...
Elow, nT,deltaP] = uploadHITEMPOld(RawDataFile);
else
disp('Wrong! Check your inputs.') end
% = /\= Loading partition func
parsumdat = load(parasumFile);
trow = Temp-69; % Temperature begins with 70 K in file. Partialfunc_ref = parsumdat(296-69, colmin:colmax);
Partialfunc = parsumdat(trow, colmin:colmax);
% =/\= Sets the Air Pressure induced Shifts
wavenumbershift = wavenumber + deltaP*p;
% =/\= Sets the Lorentzian HWHM HWHM_L = (((296/Temp)).^(nT)).*((AirHWHM.*(p-ps))+(SelfHWHM.*ps));
% -------- =/\= The simulation =/\= -------------------------------------
% =/\= Calculating the optical depth for the bands per species [tauSpectra]=CallOpticalDepthFunc(wavenumbershift, plotWavenumber, HWHM_L, S0Intensity, Temp,
Elow, Partialfunc,Partialfunc_ref, ISOVALUE, ISONR, p, ps,opticallength);
% .... =/\= The Calculation of the emittance and the emission spectra.
emittanceSpectra = (1 - exp(-tauSpectra)); emissionSpectra = emittanceSpectra '.Planck_func(plotWavenumber,Temp);
% Saving data disp('... saving! ')
disp(' ') save('OpticalDepthSimulation');
function [ISO,wavenumber,Sintensity,AirHWHM,SelfHWHM,lowerE,...
nT,deltaP,gUpper,glower] = uploadHITRAN( filename )
% -------- =/\= Upload data =/\= -------------------------------- fid = fopen(filename);
HITRANdata = textscan(fid,...
'%s %f %f %f %f %f %f %f %f %f %78c %f %f'); % '%s %f %f %f %f %f %f %f %f %f %79c %f %f'); % This is needed for some species like CH4
fclose(fid);
% -------- =/\= Upload data =/\= --------------------------------
ISO = HITRANdata1,2; wavenumber = HITRANdata1,3;
Sintensity = HITRANdata1,4;
% Acoeff = HITRANdata1,5; AirHWHM = HITRANdata1,6;
SelfHWHM = HITRANdata1,7;
lowerE = HITRANdata1,8; nT = HITRANdata1,9;
deltaP = HITRANdata1,10;
gUpper = HITRANdata1,12;
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glower = HITRANdata1,13;
end
function [ISO,wavenumber,Sintensity,AirHWHM,SelfHWHM,lowerE,...
nT,deltaP] = uploadHITEMPOld( filename )
% -------- =/\= Upload data =/\= --------------------------------
mid = fopen(filename);
HITRANdata = textscan(mid,... '%s %u %f %f %f %f %f %f %f %f %48c');
fclose(mid);
% -------- =/\= Upload data =/\= --------------------------------
ISO = HITRANdata1,2; wavenumber = HITRANdata1,3;
Sintensity = HITRANdata1,4;
% Rcoeff = HITRANdata1,5; AirHWHM = HITRANdata1,6;
SelfHWHM = HITRANdata1,7;
lowerE = HITRANdata1,8; nT = HITRANdata1,9;
deltaP = HITRANdata1,10;
end
function [LPlanck] = Planck_func(v,T)
% .... =/\= Constants ..... fradiationconst = 1.191062e-12; % [W cm^2 /sr]
sradiationconst = 1.438786; % [K cm]
% .... =/\= The Calculation of Planck's function .....
dominator = fradiationconst*(v.^3); expvalues = (sradiationconst/T).*v;
nominator = exp(expvalues)-1;
LPlanck = dominator./nominator;
% end of Planck_func func
end
% end CallEmissionFunc func end
78 Appendix A: Code for flame investigation
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A.4 FlameEmissionSimulations
Extraction of an example of the main code for simulating the flame emission in MATLAB
Extraction of the code:
% Program: FlameEmissionSimulations.m
% last modified: 12-05-02 % 2009/2010 (c) Susan Lindecrantz,
% Lund University - Faculty of Engineering
% About:
% ---------------------------------------------------------------------
% Main program caling the function CallEmissionSpectra.m to calculating the % emission of each species under investigation for the investigated region.
% The emission is not dependent on the gas to be either optical thick or thin.
% For the flame experiment the partial pressures (species mole fractions) and % the temperature has been estimated by CHEMKIN simulation of the flame.
% Assumes the medium is 'hot' (i.e. emission is strong) and
% No external light source + neglecting line-of-sight absorption and no scattering % Assuming homogenity, line-of-sight measurement.
% % Variables:
% ---------------------------------------------------------------------
% emissionSpectra_species_point]_[flame – the result; simulated emission spectra for the investigated region % emittanceSpectra_species_point]_[flame – the result; the emittance spectra for the investigated region
% tauSpectra_species_point]_[flame – the result; optical depth spectra for the investigated region
% plotWavenumber_species_point]_[flame [ cm-1 ] – the investigated region % maxWaveNr – maximum value of the investigated region
% minWaveNr – minimum value of the investigated region
% resolution – resolution of the investigated region % Temp – temperature in [ K ]
% ISOVALUE_species – A vector of all isotopic values for the molecule accordingly to HITRAN % p [ atm ] – total pressure
% ps_species [ atm ] – partial pressure for the species investigated, ps = x*p where x is the species mole fraction.
% opticalpath length [ cm ] – the optical path length estimated for gas column investigated. % RawDataFile_species [ .txt ] – file containing the vector of data from HITRAN or HITEMP generated by JavaHAWK.
% parasumFile [ .txt ]– file containing the partition function values as function of temperature, values given in HITRAN’s
% ‘parasum.dat’ file. This file needs to be downloaded and first row removed to be able to be processed. % colmax_species – maximum value of the col position in parasumFile
% colmin_species – minimum value for the col position in parasumFile
% hiTYPE - can obtain values ‘HITRAN’ or ‘HITEMP95’ depending % on what kind of file is uploaded. New HITEMP2010 is in the same format as HITRAN.
% Note! Sometimes HITEMP95 don’t work – something with g-values.
% ---------------------------------------------------------------------
% Calling the CallEmissionSpectra.m for each measurement point, Species: CO2
% Reaction zone, phi = 1.6 [plotWavenumber, emissionSpectra_CO2_R_phi16, emittanceSpectra_CO2_R_phi16,
tauSpectra_CO2_R_phi16]=CallEmissionFunc(1500,6000, 0.02,1752,1, (1*0.03),7, 'HITEMP95',
'296_C02_hitemp1000k_1500_6000_readable.txt', 'parsumData.txt', 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-6 3.957e-6 1.472e-6 4.446e-8 1.654e-8]);
% Reaction zone + 1mm, phi = 1.6
[plotWavenumber, emissionSpectra_CO2_Rp1_phi16, emittanceSpectra_CO2_Rp1_phi16, tauSpectra_CO2_Rp1_phi16]=CallEmissionFunc(1500, 6000, 0.02,1794,1, (1*0.0348),7,
'HITEMP95','296_C02_hitemp1000k_1500_6000_readable.txt', 'parsumData.txt', 8, 17, [0.9842 1.106e-2 3.947e-3 7.339e-4
4.434e-5 8.246e-6 3.957e-6 1.472e-6 4.446e-8 1.654e-8]);
….
etc.
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% Saving all data
save('Result_SimulatedSpectrasC02);
….
etc.
80 Appendix B: Code for engine investigation
Susan Lindecrantz | LTH
Appendix B: Code for engine investigation
B.1 EngineOpticalDepthAndEmissionSimulations
Example of the main code for determining the optical depth and emission for the engine simulation data in MATLAB
% Program: EngineOpticalDepthAndEmissionSimulations.m
% last modified: 12-05-02 % 2009/2010 (c) Susan Lindecrantz,
% Lund University - Faculty of Engineering
% About:
% --------------------------------------------------------------------- % Main program caling the function CallEmissionSpectra.m and indirectly CallOpticalDepthFunc m to
% calculating the emission and the optical depth for the investigated region and the two extreme measurements
% points P1 and P4. Only two species is under investigation for the three considered band regions. %
% Variables:
% --------------------------------------------------------------------- %
% emissionSpectra_species_band)_[CADpoint – simulated emission spectra for given species
% at given band region and species, for the measurement point % emittanceSpectra_species_band_[CADpoint – simulated emittance spectra for given species
% at given band region and species, for the measurement point
% tauSpectra_species_band_[CADpoint – the optical depth of the spectra spectra for given % species at given band region and species, for the measurement point
% plotWavenumber_band [ cm-1 ] - investigated region for the given band region.
% RawDataFile_species [ .txt ] – file containing the line positions and the hitran data for each species generated by JavaHAWK.
% maxWaveNr_band – maximum value of the investigated region
% minWaveNr_band – minimum value of the investigated region % resolution – resolution of the investigated region
% Temp – temperature in [ K ]
% p [ atm ] – total pressure % ps_species_CADpoint [ atm ] – partial pressure for the species investigated, ps = x*p where x is the species
% mole fraction, for the measurement point
% opticalpath length [ cm ] – the optical path length estimated for gas column investigated. % parasumFile [ .txt ]– file containing the partition function values as function of temperature, values given in HITRAN's
% 'parasum.dat' file. This file needs to be downloaded and first row removed to be able to be processed.
% colmax_species – maximum value of the col position in parasumFile % colmin_species – minimum value for the col position in parasumFile
% ISOVALUE_species – A vector of all isotopic values for the molecule accordingly to HITRAN
% ---------------------------------------------------------------------
% Measuring Point P1: P = 35.05*0.98692 Atm, T = 1008 K
% Calling the CallEmissionSpectra.m for each measurement point, Species: CO2, X_CO2 = 0.1051
% Band 1 – Region: 2250 -2498 cm-1
[plotWavenumber_Band1, emissionSpectra_CO2_Band1_P1, emittanceSpectra_CO2_Band1_P1,
tauSpectra_CO2_Band1_P1]=CallEmissionFunc(2250,2498, 0.02,1008,(35.05*0.98692), (35.05*0.98692*0.1051),8.1, 'HITRAN','296_C02_hi04_1500_6000_readable.txt', 'parsumData.txt', 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-6
3.957e-6 1.472e-6 4.446e-8 1.654e-8]);
% Band 2 – Region: 3450 -3915 cm-1
[plotWavenumber_Band2, emissionSpectra_CO2_Band2_P1, emittanceSpectra_CO2_Band2_P1, tauSpectra_CO2_Band2_P1]=CallEmissionFunc(3450,3915, 0.02,1008,(35.05*0.98692), (35.05*0.98692*0.1051),8.1,
'HITRAN','296_C02_hi04_1500_6000_readable.txt', 'parsumData.txt', 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-6 3.957e-6 1.472e-6 4.446e-8 1.654e-8]);
% Band 3 – Region: 4840-5125 cm-1
[plotWavenumber_Band3, emissionSpectra_CO2_Band3_P1, emittanceSpectra_CO2_Band3_P1,
tauSpectra_CO2_Band3_P1]=CallEmissionFunc(4840,5125, 0.02,1008,(35.05*0.98692), (35.05*0.98692*0.1051),8.1, 'HITRAN','296_C02_hi04_1500_6000_readable.txt', 'parsumData.txt', 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-6
3.957e-6 1.472e-6 4.446e-8 1.654e-8]);
% Calling the CallEmissionSpectra.m for each measurement point, Species: H20, X_H20 = 0.1183
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% Band 1 – Region: 2250 -2498 cm-1 [plotWavenumber_Band1, emissionSpectra_H20_Band1_P1, emittanceSpectra_H20_Band1_P1,
tauSpectra_H20_Band1_P1]=CallEmissionFunc(2250,2498, 0.02,1008,(35.05*0.98692), (35.05*0.98692*0.1183),8.1, 'HITRAN',
'296_H20_hitran09_1500_6000_readable.txt', 'parsumData.txt', 2, 7,[ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7 1.158e-7]);
% Band 2 – Region: 3450 -3915 cm-1 [plotWavenumber_Band2, emissionSpectra_H20_Band2_P1, emittanceSpectra_H20_Band2_P1,
tauSpectra_H20_Band2_P1]=CallEmissionFunc(3450,3915, 0.02,1008,(35.05*0.98692), (35.05*0.98692*0.1183),8.1, 'HITRAN',
'296_H20_hitran09_1500_6000_readable.txt', 'parsumData.txt', 2, 7, [ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7 1.158e-7]);
% Band 3 – Region: 4840-5125 cm-1
[plotWavenumber_Band3, emissionSpectra_H20_Band3_P1, emittanceSpectra_H20_Band3_P1,
tauSpectra_H20_Band3_P1]=CallEmissionFunc(4840,5125, 0.02,1008,(35.05*0.98692), (35.05*0.98692*0.1183),8.1, 'HITRAN','296_H20_hitran09_1500_6000_readable.txt', 'parsumData.txt', 2, 7,[ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7
1.158e-7]);
% Measuring Point P4: P = 2.01*0.98692 Atm, T = 528K
% Calling the CallEmissionSpectra.m for each measurement point, Species: CO2, X_CO2 = 0.1051
% Band 1 – Region: 2250 -2498 cm-1 [plotWavenumber_Band1, emissionSpectra_CO2_Band1_P4, emittanceSpectra_CO2_Band1_P4,
tauSpectra_CO2_Band1_P4]=CallEmissionFunc(2250,2498, 0.02,528,(2.01*0.98692), (2.01*0.98692*0.1051),8.1,
'HITRAN','296_C02_hi04_1500_6000_readable.txt', 'parsumData.txt', 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-6 3.957e-6 1.472e-6 4.446e-8 1.654e-8]);
% Band 2 – Region: 3450 -3915 cm-1
[plotWavenumber_Band2, emissionSpectra_CO2_Band2_P4, emittanceSpectra_CO2_Band2_P4,
tauSpectra_CO2_Band2_P4]=CallEmissionFunc(3450,3915, 0.02,528,(2.01*0.98692), (2.01*0.98692*0.1051),8.1, 'HITRAN','296_C02_hi04_1500_6000_readable.txt', 'parsumData.txt', 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-6
3.957e-6 1.472e-6 4.446e-8 1.654e-8]);
% Band 3 – Region: 4840-5125 cm-1
[plotWavenumber_Band3, emissionSpectra_CO2_Band3_P4, emittanceSpectra_CO2_Band3_P4, tauSpectra_CO2_Band3_P4]=CallEmissionFunc(4840,5125, 0.02,528,(2.01*0.98692), (2.01*0.98692*0.1051),8.1,
'HITRAN','296_C02_hi04_1500_6000_readable.txt', 'parsumData.txt', 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-6
3.957e-6 1.472e-6 4.446e-8 1.654e-8]);
% Calling the CallEmissionSpectra.m for each measurement point, Species: H20, X_H20 = 0.1183
% Band 1 – Region: 2250 -2498 cm-1 [plotWavenumber_Band1, emissionSpectra_H20_Band1_P4, emittanceSpectra_H20_Band1_P4,
tauSpectra_H20_Band1_P4]=CallEmissionFunc(2250,2498, 0.02,528,(2.01*0.98692), (2.01*0.98692*0.1183),8.1, 'HITRAN',
'296_H20_hitran09_1500_6000_readable.txt', 'parsumData.txt', 2, 7,[ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7 1.158e-7]);
% Band 2 – Region: 3450 -3915 cm-1 [plotWavenumber_Band2, emissionSpectra_H20_Band2_P4, emittanceSpectra_H20_Band2_P4,
tauSpectra_H20_Band2_P4]=CallEmissionFunc(3450,3915, 0.02,528,(2.01*0.98692), (2.01*0.98692*0.1183),8.1, 'HITRAN',
'296_H20_hitran09_1500_6000_readable.txt', 'parsumData.txt', 2, 7, [ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7 1.158e-7]);
% Band 3 – Region: 4840-5125 cm-1 [plotWavenumber_Band3, emissionSpectra_H20_Band3_P4, emittanceSpectra_H20_Band3_P4,
tauSpectra_H20_Band3_P4]=CallEmissionFunc(4840,5125, 0.02,528,(2.01*0.98692), (2.01*0.98692*0.1183),8.1,
'HITRAN','296_H20_hitran09_1500_6000_readable.txt', 'parsumData.txt', 2, 7,[ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7 1.158e-7]);
% save all data
save('Result_EngineSimulationOpticalDepthVSEmission');
82 Appendix B: Code for engine investigation
Susan Lindecrantz | LTH
B.2 EngineTemperatureSimulations
Extraction of an example of the main code for calculating the temperature with emission
for the engine simulation data in MATLAB
% Program: EngineTemperatureSimulations.m
% last modified: 12-05-02 % 2009/2010 (c) Susan Lindecrantz,
% Lund University - Faculty of Engineering
% About:
% ---------------------------------------------------------------------
% Main program caling the function CallEmissionSpectra.m and indirectly CallOpticalDepthFunc m to % calculating the temperature from the ratio of emission bands for true blackbody emissitivity = 1and for
% emissitivity < 1. For this the emissitivity and hence the emission for the investigated region and the
% measurements is to determined and the blackbody curve. %
% The following band is considered; Band 1 at 2250 -2498 cm-1 and Band 2 at 3450 -3915 cm-1.
% All 4 measuring points in table (4.2) are caulcated; The concentration is assumed to be 10.51% C02 and % 11.83% H20 as given in the induction stagte by Eq. (2.24) for lambda = 1.2
%
% Variables: % ---------------------------------------------------------------------
%
% emissionBBRatio_CADPoint – the result, the band ratio vector as function of Temperature, % emissitivity = 1
% emissionHITRANRatio_CADPoint – the result, the band ratio vector as function of Temperature, emissitivity < 1
% opticalDepth_band - containing the summed optical depth for the different species for band region % emittance_band – calculated emittance using opticalDepth_bandfor each band region
% emission_band – the emission of the summed effect of the different species from emittance_band
% emissionSpectra_species_band)_[CADpoint – simulated emission spectra for given species at % given band region and species, for the measurement point
% emittanceSpectra_species_band_[CADpoint – simulated emittance spectra for given species at
% given band region and species, for the measurement point % tauSpectra_species_band_[CADpoint – the optical depth of the spectra spectra for given species at
% given band region and species, for the measurement point % plotWavenumber_band [ cm-1 ] - investigated region for the given band region.
% RawDataFile_species [ .txt ] – file containing the line positions and the hitran data for each species generated by
JavaHAWK. % maxWaveNr_band – maximum value of the investigated region
% minWaveNr_band – minimum value of the investigated region
% resolution – resolution of the investigated region % TempVector – vector containg the temperature range in [ K ]
% p [ atm ] – total pressure
% ps_species_[CADpoint [ atm ] – partial pressure for the species investigated, ps = x*p where is the species % mole fraction, for the measurement point
% opticalpath length [ cm ] – the optical path length estimated for gas column investigated.
% parasumFile [ .txt ]– file containing the partition function values as function of temperature, values given in % HITRAN’s ‘parasum.dat’ file. This file needs to be downloaded and first row removed to be able to be processed.
% colmax_species – maximum value of the col position in parasumFile
% colmin_species – minimum value for the col position in parasumFile % ISOVALUE_species – A vector of all isotopic values for the molecule accordingly to HITRAN
% filterFile [.txt] – This file contains the filer data used for the simulation per band region.
% calibration_band - Response of the setup instruments for the band region, to be measured. Here set to 1; % ---------------------------------------------------------------------
% =/\= Setting the wavenumber region for the bands
plotWavenumber_B1 = maxWaveNr_B1:resolution: maxWaveNr_B1;
plotWavenumber_B2 = maxWaveNr_B2:resolution: maxWaveNr_B2;
% Simulation Temperature Determination for
% Measuring Point P1: P = 35.05*0.98692 Atm, T = 1008 K
% Comment; Calculating the emission and multipying with filter, then summing the
% intensity before dividing it between the two bands.
% For Each Temperature the Emission is…
for T = 1:length(TempVector)
% obtaining the Planck function for each band region
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Planck_B1 = Planck_func(plotWavenumberB1,TempVector(T));
Planck_B2 = Planck_func(plotWavenumberB2,TempVector(T));
% Taking the filter into account Planckfilter_B1 = PlanckB1.* uploadFilter(plotWavenumber_B1,filterFile_B1);
Planckfilter_B2 = PlanckB2.* uploadFilter(plotWavenumber_B1,filterFile_B1);
% Calibration of the setup (including spectral response of setup) calibrationRatio = calibration_B2./calibration_B1;
% Calling the CallEmissionSpectra.m for each measurement point, Species: CO2, X_CO2 = 0.1051
% Band 1 – Region: 2250 -2498 cm-1
[plotWavenumber_Band1, emissionSpectra_CO2_Band1_P1, emittanceSpectra_CO2_Band1_P1,
tauSpectra_CO2_Band1_P1]=CallEmissionFunc(2250,2498, 0.02, TempVector(T),(35.05*0.98692), (35.05*0.98692*0.1051),8.1, ‘HITRAN’,’296_C02_hi04_1500_6000_readable.txt’, ‘parsumData.txt’, 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-
6 3.957e-6 1.472e-6 4.446e-8 1.654e-8]);
% Band 2 – Region: 3450 -3915 cm-1
[plotWavenumber_Band2, emissionSpectra_CO2_Band2_P1, emittanceSpectra_CO2_Band2_P1, tauSpectra_CO2_Band2_P1]=CallEmissionFunc(3450,3915, 0.02, TempVector(T),(35.05*0.98692), (35.05*0.98692*0.1051),8.1,
‘HITRAN’,’296_C02_hi04_1500_6000_readable.txt’, ‘parsumData.txt’, 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-6 3.957e-6 1.472e-6 4.446e-8 1.654e-8]);
% Calling the CallEmissionSpectra.m for each measurement point, Species: H20, X_H20 = 1.2*X_C02 = 0.1183
% Band 1 – Region: 2250 -2498 cm-1 [plotWavenumber_Band1, emissionSpectra_H20_Band1_P1, emittanceSpectra_H20_Band1_P1,
tauSpectra_H20_Band1_P1]=CallEmissionFunc(2250,2498, 0.02, TempVector(T),(35.05*0.98692), (35.05*0.98692*0.1183),8.1,
‘HITRAN’, ‘296_H20_hitran09_1500_6000_readable.txt’, ‘parsumData.txt’, 2, 7,[ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7 1.158e-7]);
% Band 2 – Region: 3450 -3915 cm-1
[plotWavenumber_Band2, emissionSpectra_H20_Band2_P1, emittanceSpectra_H20_Band2_P1,
tauSpectra_H20_Band2_P1]=CallEmissionFunc(3450,3915, 0.02, TempVector(T),(35.05*0.98692), (35.05*0.98692*0.1183),8.1, ‘HITRAN’, ‘296_H20_hitran09_1500_6000_readable.txt’, ‘parsumData.txt’, 2, 7, [ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7
1.158e-7]);
% Summing the optical depth for the different species; water and CO2; and band regions
opticalDepth_B1 = tauSpectra_H20_Band1_P1 + tauSpectra_CO2_Band1_P1; opticalDepth _B2 = tauSpectra_H20_Band2_P1 + tauSpectra_CO2_Band2_P1;
% Calculating the emittance for the different species; water and CO2; and band regions
emittance_B1 = 1-exp(-opticalDepth_B1);
emittance_B2 = 1-exp(-opticalDepth_B2);
% .... =/\= The Calculation of the emittance spectra .....
% + taking the filter into account emission_B1 = (Planckfilter_B1.*emittance_B1');
emission_B2 = (Planckfilter_B2.*emittance_B2');
% Simulation result True BB: The ratio of the summed band intensities. emissionBBRatio(T) = calibrationRatio.* (sum(Planckfilter_B2)/sum(Planckfilter_B1));
% Simulation result emission with emissitivity less than 1: The ratio of the summed band intensities. emissionHITRANRatio(T) = calibrationRatio.* (sum(emission_B2)/sum(emission_B1));
% Printing out calculation progress if count == 5
percent = (T)/(length(tempertureVector))*100; D = ['--> Processing temperature ... ',num2str(fix(percent)),'%'];
disp(D)
count = 0; else
count = count +1;
end
end
84 Appendix B: Code for engine investigation
Susan Lindecrantz | LTH
% save all data Save(‘Result_EngineTemperatureSimulation_P1’);
…
etc
function [filter] = uploadFilter(plotWavenumber,filterFile)
% =/\= Loading filter data for given band region and interpolating data
% within the region to fit plotWavenumber
fid = fopen( filterFile); filterData = textscan(fid,'%f %f');
fclose(fid);
filterDataVector(:,1) = filterData 1,1; filterDataVector (:,2) = filterData 1,2;
filter = interp1(filterDataVector (:,1), filterDataVector (:,2),plotWavenumber,'cubic');
end
function [LPlanck] = Planck_func(v,T)
% .... =/\= Constants ..... fradiationconst = 1.191062e-12; % [W cm^2 /sr]
sradiationconst = 1.438786; % [K cm]
% .... =/\= The Calculation of Planck's function .....
dominator = fradiationconst*(v.^3); expvalues = (sradiationconst/T).*v;
nominator = exp(expvalues)-1;
LPlanck = dominator./nominator;
% end of Planck_func func
end
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B.3 EngineConcentrationSimulations
Extraction of an example of the main code for calculating the concentration with emission for the engine simulation data in MATLAB
% Program: EngineConcentrationSimulations.m
% last modified: 12-05-02
% 2009/2010 (c) Susan Lindecrantz, % Lund University - Faculty of Engineering
% About: % ---------------------------------------------------------------------
% Main program caling the function CallEmissionSpectra.m and indirectly CallOpticalDepthFunc m to
% calculating the concentration from the ratio of emission bands for emissitivity < 1. % The temperature is KNOWN factor!
%
% The following band is considered; Band 2 at 3450 -3915 cm-1 cm-1 and Band 3 at 4840-5125 cm-1. % All 4 measuring points in table (4.2) are caulcated; The relation between water and C02 is assumed to be
% the same. times 9moels/8moles = 1.2 H20 on each mole fraction of C02.
% % Variables:
% ---------------------------------------------------------------------
% % emissionBBRatio_CADPoint – the result, the band ratio vector as function of Temperature, emissitivity = 1
% emissionHITRANRatio_CADPoint – the result, the band ratio vector as function of Temperature, emissitivity < 1
% opticalDepth_band - containing the summed optical depth for the different species for band region % emittance_band – calculated emittance using opticalDepth_bandfor each band region
% emission_band – the emission of the summed effect of the different species from emittance_band
% emissionSpectra_species_band)_[CADpoint – simulated emission spectra for given species at % given band region and species, for the measurement point
% emittanceSpectra_species_band_[CADpoint – simulated emittance spectra for given species at
% given band region and species, for the measurement point % tauSpectra_species_band_[CADpoint – the optical depth of the spectra spectra for given species at
% given band region and species, for the measurement point
% plotWavenumber_band [ cm-1 ] - investigated region for the given band region. % RawDataFile_species [ .txt ] – file containing the line positions and the hitran data for each species generated by
JavaHAWK. % maxWaveNr_band – maximum value of the investigated region
% minWaveNr_band – minimum value of the investigated region
% resolution – resolution of the investigated region % ConcVector – vector containg the mole fractions range for CO2 in [ K ]
% p [ atm ] – total pressure
% ps_species_[CADpoint [ atm ] – partial pressure for the species investigated, ps = x*p where x is the % species mole fraction, for the measurement point
% opticalpath length [ cm ] – the optical path length estimated for gas column investigated.
% parasumFile [ .txt ]– file containing the partition function values as function of temperature, values given in HITRAN’s % ‘parasum.dat’ file. This file needs to be downloaded and first row removed to be able to be processed.
% colmax_species – maximum value of the col position in parasumFile
% colmin_species – minimum value for the col position in parasumFile % ISOVALUE_species – A vector of all isotopic values for the molecule accordingly to HITRAN
% filterFile [.txt] – This file contains the filer data used for the simulation per band region.
% calibration_band - Response of the setup instruments for the band region, to be measured. Here set to 1; % ---------------------------------------------------------------------
% Simulation Temperature Determination for
% Measuring Point P1: P = 35.05*0.98692 Atm, T = 1008 K
% Calculating the emission and multipying with filter, then summing the
% intensity before dividing it between the two bands. ConcVector = (0.1051:0.10:1)';
filterFile_B3 = 'filter[NB-2050-012 nm]CWL4881.txt';
filterFile_B2 = 'filter[NB-2690-050 nm]CWL3692.txt'; calibration_B3 = 1;
calibration_B2 = 1;
count = 0;
% Simulation Concentration Determination for
% Measuring Point P1: P = 35.05*0.98692 Atm, T = 1008 K
% Calculating the emission and multipying with filter, then summing the
% intensity before dividing it between the two bands.
86 Appendix B: Code for engine investigation
Susan Lindecrantz | LTH
% For Each Concentration Step the Emission is… for ConcNr = 1:length(ConcVector)
% Concentration in mole fraction of total, with (moleH20/moleC02) = 9/8 mole fractionC02 = ConcVector(ConcNr); mole fractionH20 = (9/8)*mole fractionC02;
% Calling the CallEmissionSpectra.m for each measurement point, Species: CO2, X_CO2 = 0.1051
% Band 2 – Region: 3450 -3915 cm-1 [~, emissionSpectra_CO2_Band2_P1, emittanceSpectra_CO2_Band2_P1,
tauSpectra_CO2_Band2_P1]=CallEmissionFunc(3450,3915,...
0.02,1008,(35.05*0.98692), (35.05*0.98692* mole fractionC02),8.1, 'HITRAN','296_C02_hi04_1500_6000_readable.txt', ... 'parsumData.txt', 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-6 3.957e-6 1.472e-6 4.446e-8 1.654e-8]);
% Band 3 – Region: 4840-5125 cm-1
[~, emissionSpectra_CO2_Band3_P1, emittanceSpectra_CO2_Band3_P1,
tauSpectra_CO2_Band3_P1]=CallEmissionFunc(4840,5125,... 0.02,1008,(35.05*0.98692), (35.05*0.98692* mole fractionC02),8.1, 'HITRAN','296_C02_hi04_1500_6000_readable.txt', ...
'parsumData.txt', 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-6 3.957e-6 1.472e-6 4.446e-8 1.654e-8]);
% Calling the CallEmissionSpectra.m for each measurement point, Species: H20, X_H20 = 1.2*X_C02 = 0.1183
% Band 2 – Region: 3450 -3915 cm-1
[plotWavenumber_Band2, emissionSpectra_H20_Band2_P1, emittanceSpectra_H20_Band2_P1,
tauSpectra_H20_Band2_P1]=CallEmissionFunc(3450,3915,... 0.02,1008,(35.05*0.98692), (35.05*0.98692* mole fractionH20),8.1, 'HITRAN', '296_H20_hitran09_1500_6000_readable.txt', ...
'parsumData.txt', 2, 7, [ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7 1.158e-7]);
% Band 3 – Region: 4840-5125 cm-1
[plotWavenumber_Band3, emissionSpectra_H20_Band3_P1, emittanceSpectra_H20_Band3_P1, tauSpectra_H20_Band3_P1]=CallEmissionFunc(4840,5125,...
0.02,528,(2.01*0.98692), (2.01*0.98692* mole fractionH20),8.1, 'HITRAN','296_H20_hitran09_1500_6000_readable.txt',
'parsumData.txt', ... 2, 7,[ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7 1.158e-7]);
% Summing the optical depth for the different species; water and CO2; and band regions
opticalDepth_B3 = tauSpectra_H20_Band1_P1 + tauSpectra_CO2_Band1_P1;
opticalDepth_B2 = tauSpectra_H20_Band2_P1 + tauSpectra_CO2_Band2_P1;
% Calculating the emittance for the different species; water and CO2; and band regions emittance_B3 = 1-exp(-opticalDepth_B3);
emittance_B2 = 1-exp(-opticalDepth_B2);
% obtaining the Planck function for each band region Planck_B3 = Planck_func(plotWavenumber_Band1,ConcVector(ConcNr)); Planck_B2 = Planck_func(plotWavenumber_Band2,ConcVector(ConcNr));
% Taking the filter into account Planckfilter_B3 = Planck_B3.* uploadFilter(plotWavenumber_Band1,filterFile_B3);
Planckfilter_B2 = Planck_B2.* uploadFilter(plotWavenumber_Band2,filterFile_B2);
% Calibration of the setup (including spectral response of setup) calibrationRatio = calibration_B2./calibration_B3;
% .... =/\= The Calculation of the emittance spectra .....
% + taking the filter into account emission_B3 = emittance_B3.*Planckfilter_B3';
emission_B2 = emittance_B2.*Planckfilter_B2';
% Simulation result emission with emissitivity less than 1: The ratio of the summed band intensities.
emissionHITRANRatio(ConcNr) = calibrationRatio.* (sum(emission_B2)/sum(emission_B3));
% Printing out calculation progress if count == 2
percent = (ConcNr)/(length(ConcVector))*100;
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D = ['--> Processing concentration ... ',num2str(fix(percent)),'%'];
disp(D)
count = 0; else
count = count +1;
end
end
% save all data
save('Result_EngineConcentrationSimulation_P1.mat');
% …
% etc
88 Appendix B: Code for engine investigation
Susan Lindecrantz | LTH
B.4 CallTwoLineMethodAbsorptionTemperatureSimulation.m Example of the code for calculating the temperature dependence of the ratio of absorpance from two chosen lines for the engine simulation data in MATLAB
function [ratioAbs] = CallTwoLineMethodAbsorptionTemperatureSimulationFunc (v0_L1, v0_L2,S0Line1,S0Line2,EuppLine1,
ElowLine1,EuppLine2, ElowLine2, QTfunc, QTfunc_ref, ISONR_L1, ISONR_L2, T)
% Program: CallTwoLineMethodAbsorptionTemperatureSimulation.m % last modified: 12-05-02
% 2009/2010 (c) Susan Lindecrantz,
% Lund University - Faculty of Engineering
% About:
% --------------------------------------------------------------------- % The function calculates the ratio between absorpbance for two lines accordingkly
% to Eq. (4.5) as functiuon of temperature.
% The absorpbance can be obtained from the measuring the transmission at wavelength v. % This is to be compared with the measured ratio of the two integrated absorbance
% to obtain the temperature.
% The partition functions values need to be uploaded a prior. %
% Variables:
% --------------------------------------------------------------------- % parasumFile = file from HITRAN called parasumData.txt
% minParasum = first column value in the liting of parasumData.txt for species
% maxParasum = last column value in the liting of parasumData.txt for species % Tmax = maximum temperature
% Tmin = minimum temperature
% Resolution = resolution of spectra % v0_L1 = wavenumber for line 1
% S0_L1 = line strengthfor line 1 at 296K
% Elow_L1 = lower energy state for line 1 % Eupp_L1 = upper energy state for line 1
% ISONR_L1 = isotopic number for line 1 % v0_L2 = wavenumber for line 2
% S0_L2 = line strengthfor line 2 at 296K
% Elow_L2 = lower energy state for line 2 % Eupp_L2 = upper energy state for line 2
% ISONR_L2 = isotopic number for line 2
% ratio = the ratio from Eq. (4.5) as function of Temperature % ---------------------------------------------------------------------
% =/\= Constants =/\=
fradiationconst = 1.191062e-12; % [W cm^2 /sr] sradiationconst = 1.438786; % [K cm]
NL = 2.68676e19; % [ molecules cm^-3 atm^-1] Lochsmidths' number
% For Each Spectral Line for temp = 1:length(T)
% Get values of the partition functions and abundance QT_L1 = QTfunc(temp,ISONR_L1);
QTref_L1 = QTfunc_ref(ISONR_L1); QT_L2 = QTfunc(temp,ISONR_L2);
QTref_L2 = QTfunc_ref(ISONR_L2);
% .... =/\= The Calculation of the temperature .....
% Transform the SInt (cm/molecules) to SInt (cm^-2 atm^-1) SInt0_L1 = S0Line1*NL*(296/T(temp));
SInt0_L2 = S0Line2*NL*(296/T(temp));
% Obtaining the temperature corrected line intensity
% Unit (cm^-2 atm^-1) [ SIntT_L1 ] = SintensityTempConversion(S0Line1,T(temp),Elow_L1,... QT_L1,QTref_L1,v0_L1);
[ SIntT_L2 ] = SintensityTempConversion(S0Line2,T(temp),Elow_L2,...
QT_L2,QTref_L2,v0_L2);
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% Ratio of R(T) = S(T,v01)/S(T,v02) ratioAbs(temp) = SIntT_L2/SIntT_L1;
% Printing out calculation progress steps = round(length(T)*0.1);
if count == steps percent = (temp)/(length(T))*100;
D = ['--> Processing ... ',num2str(fix(percent)),'%'];
disp(D) count = 0;
else
count = count +1; end
end
end
% end CallTwoLineMethodAbsorptionTemperatureSimulationFunc
end
90 Appendix B: Code for engine investigation
Susan Lindecrantz | LTH
B.5 EngineConcentrationLEDSimulations
Extraction of an example of the main code for calculating the concentration with absorption with LED light source for the engine simulation data in MATLAB
% Program: EngineConcentrationLEDSimulations.m % last modified: 12-05-02
% 2009/2010 (c) Susan Lindecrantz,
% Lund University - Faculty of Engineering
% About:
% --------------------------------------------------------------------- % Main program caling the function CallEmissionSpectra.m and indirectly CallOpticalDepthFunc m to
% calculating the transmittance in function of concentration from given wavenumber! Light Source: LED
% % The following band is considered; Band 3 at 4840-5125 cm-1.
% All 4 measuring points in table (4.2) are caulcated; The relation between water and C02 is assumed to be
% the same. H20 times 9/8 moles = 1.2 H20 on each mole fraction of C02.
…
etc
% For Each Concentration Step the Emission is…
for ConcNr = 1:length(ConcVector)
% Concentration in mole fraction of total, with (moleH20/moleC02) = 9/8 mole fractionC02 = concVector(ConcNr);
mole fractionH20 = (9/8)*mole fractionC02;
…
etc
% Simulation Concentration Determination for
% Measuring Point P1: P = 2.01*0.98692 Atm, T = 528 K
% =/\= Calculating the emissivity for the bands per species
% Band 3 – Region: 4840-5125 cm-1 C02
[plotWavenumber_Band3, emissionSpectra_CO2_Band3_P4(n) , emittanceSpectra_CO2_Band3_P4(n) , tauSpectra_CO2_Band3_P4(n) ]=CallEmissionFunc(4840,5125, 0.02,528,(2.01*0.98692), (2.01*0.98692* mole fractionC02),8.1,
‘HITRAN’,’296_C02_hi04_1500_6000_readable.txt’, ‘parsumData.txt’, 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-
6 3.957e-6 1.472e-6 4.446e-8 1.654e-8]);
% Band 3 – Region: 4840-5125 cm-1 H20 [plotWavenumber_Band3, emissionSpectra_H20_Band3_P4(n) , emittanceSpectra_H20_Band3_P4(n) ,
tauSpectra_H20_Band3_P4(n) ]=CallEmissionFunc(4840,5125, 0.02,528,(2.01*0.98692), (2.01*0.98692* mole fractionH20),8.1,
‘HITRAN’,’296_H20_hitran09_1500_6000_readable.txt’, ‘parsumData.txt’, 2, 7,[ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7 1.158e-7]);
% =/\= Loading The LED BandWidth + Uploading the expanded LED profile
fid = fopen(LEDfile);
LEDdata = textscan(fid,'%f %f'); fclose(fid);
LEDvector(:,1) = LEDdata1,1;
LEDvector(:,2) = LEDdata1,2;
xi = plotWavenumber ;
yi = interp1(LEDvector(:,1),...
LEDvector(:,2),xi,'cubic');
LEDwavenumber = xi;
LEDprofile = yi;
% =/\= Calculating the transmission using Beer's law
Master of Science Thesis 91
LTH | Susan Lindecrantz
% Calculaing Beers law - broadband version
upperBeerlaw=LEDprofile.*exp(-(tauSpectra_H20_Band3_P4(n)+ tauSpectra_CO2_Band3_P4 (n)) ;) lowerBeerlaw = LEDprofile;
transmittance(n)= sum(upperBeerlaw)/sum(lowerBeerlaw);
…
etc
92 Appendix B: Code for engine investigation
Susan Lindecrantz | LTH
B.6 EngineConcentrationDiodeLaserSimulations
Extraction of an example of the main code for calculating the concentration with
absorption and an Diode Laser source for the engine simulation data in MATLAB
% Program: EngineConcentrationDiodeLaserSimulations.m
% last modified: 12-05-02 % 2009/2010 (c) Susan Lindecrantz,
% Lund University - Faculty of Engineering
% About:
% ---------------------------------------------------------------------
% Main program caling the function CallEmissionSpectra.m and indirectly CallOpticalDepthFunc m to % calculating the concentration from given wavenumber! Source: Diode Laser
%
% The following band is considered; Band 3 at 4840-5125 cm-1. % All 4 measuring points in table (4.2) are caulcated; The relation between water and C02 is assumed to be
% the same. times 9moels/8moles = 1.2 H20 on each mole fraction of C02.
…
etc
diodeWavenumber = 4884.0; % 2.045 um
…
etc
% =/\= Finding the diode-wavenumber's position in plotWavenumber diodeWavenumberNR = find(plotWavenumber == diodeWavenumber)
if isempty(diodeWavenumberNR) == true
disp('Error - diode wavenumber couldn´t be found');
else
diodeWavenumber = plotWavenumber(diodeWavenumberNR)
disp('Diode wavenumber found!');
…
etc
% For Each Concentration Step the Emission is… for ConcNr = 1:length(ConcVector)
% Concentration in mole fraction of total, with (moleH20/moleC02) = 9/8 mole fractionC02 = concVector(ConcNr); mole fractionH20 = (9/8)*mole fractionC02;
…
etc
% Simulation Concentration Determination for
% Measuring Point P1: P = 2.01*0.98692 Atm, T = 528 K
% =/\= Calculating the emissivity for the bands per species
% Band 3 – Region: 4840-5125 cm-1 C02
[plotWavenumber_Band3, emissionSpectra_CO2_Band3_P4(n) , emittanceSpectra_CO2_Band3_P4(n) ,
tauSpectra_CO2_Band3_P4(n) ]=CallEmissionFunc(4840,5125, 0.02,528,(2.01*0.98692), (2.01*0.98692* mole fractionC02),8.1, ‘HITRAN’,’296_C02_hi04_1500_6000_readable.txt’, ‘parsumData.txt’, 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-
6 3.957e-6 1.472e-6 4.446e-8 1.654e-8]);
% Band 3 – Region: 4840-5125 cm-1 H20
Master of Science Thesis 93
LTH | Susan Lindecrantz
[plotWavenumber_Band3, emissionSpectra_H20_Band3_P4(n) , emittanceSpectra_H20_Band3_P4(n) ,
tauSpectra_H20_Band3_P4(n) ]=CallEmissionFunc(4840,5125, 0.02,528,(2.01*0.98692), (2.01*0.98692* mole fractionH20),8.1, ‘HITRAN’,’296_H20_hitran09_1500_6000_readable.txt’, ‘parsumData.txt’, 2, 7,[ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7
1.158e-7]);
% =/\= Calculating the transmission using Beer's law
transmittance(n) = exp(-(tauSpectra_H20_Band3_P4(n,diodeWavenumberNR)+ tauSpectra_CO2_Band3_P4 (n,diodeWavenumberNR) ) );
…
etc
94 Appendix C: Comparison between measured and simulated spectra
Susan Lindecrantz | LTH
Appendix C: Comparison between measured and simulated spectra
C.1 Comparison for 3 mm below the flame zone
C.2 Comparison for 1 mm below the flame zone
1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500-1
0
1
2
3
4
5
6x 10
-5
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Comparison between measured and simulated spectra for phi = 0.8 at 3 mm below the visible flamezone
1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500-4
-2
0
2
4
6
8
10x 10
-5
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Comparison between measured and simulated spectra for phi = 1.6 at 3 mm below the visible flamezone
measured spectra
simulated spectra
measured spectra
simulated spectra
CO
H2O
H2O
H2O
H2O
CO2
CO2
1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500-2
0
2
4
6
8x 10
-5
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Comparison between measured and simulated spectra for phi = 0.8 at 1 mm below the visible flamezone
2000 2500 3000 3500 4000 4500 5000 5500
0
0.5
1
1.5
2
2.5
x 10-3
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Comparison between measured and simulated spectra for phi = 1.6 at 1 mm below the visible flamezone
measured spectra
simulated spectra
simulated spectra
measured spectra
H2O
CO
CO
CO
CO2
CO2
H2O
H2O
H2O
H2O
CH4
H2O + CO
2
Master of Science Thesis 95
LTH | Susan Lindecrantz
C.3 Comparison at the flame zone
C.4 Comparison for 1 mm above the flame zone
2000 2500 3000 3500 4000 4500 5000 5500
0
0.5
1
1.5
2
2.5
x 10-3 Comparison between measured and simulated spectra for phi = 1.6 at visible flamezone
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
2000 2500 3000 3500 4000 4500 5000 5500
0
5
10
15
x 10-4
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Comparison between measured and simulated spectra for phi = 0.8 at visible flamezone
simulated spectra
measured spectra
simulated spectra
measured spectra
H2O + CO
2
H2O + CO
2
H2O + CO
2
H2O + CO
2
H2O
H2O CO
2
CO
CH4
CH4
CO2
CO2
CO
CO
2000 2500 3000 3500 4000 4500 5000 5500 6000
0
5
10
15
20
x 10-4
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Comparison between measured and simulated spectra for phi = 0.8 at 1 mm above the visible flamezone
2000 2500 3000 3500 4000 4500 5000 5500
0
0.5
1
1.5
2
2.5
x 10-3
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Comparison between measured and simulated spectra for phi = 1.6 at 1 mm above the visible flamezone
simulated spectra
measured spectra
simulated spectra
measured spectra
H2O + CO
2
H2O + CO
2
H2O + CO
2
H2O + CO
2CO2
CO2
H2O
H2O
CO
CO
96 Appendix C: Comparison between measured and simulated spectra
Susan Lindecrantz | LTH
C.5 Comparison for 3 mm above the flame zone
2000 2500 3000 3500 4000 4500 5000 5500
0
0.5
1
1.5
2
2.5
x 10-3
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Comparison between measured and simulated spectra for phi = 0.8 at 3 mm above the visible flamezone
2000 2500 3000 3500 4000 4500 5000 5500
0
0.5
1
1.5
2
2.5
x 10-3
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Comparison between measured and simulated spectra for phi = 1.6 at 3 mm above the visible flamezone
simulated spectra
measured spectra
simulated spectra
measured spectraCO
2
CO2
H2O
H2O
H2O + CO
2
H2O + CO
2
H2O + CO
2
H2O + CO
2
CO
CO
Master of Science Thesis 97
LTH | Susan Lindecrantz
Appendix D: Populärvetenskapling sammanfattning
This section contains the summary of the work in form of a scientific paper (Swedish:
Populärvetenskapling sammanfattning). It only includes the part concerning the flame
measurement.
98 Appendix D: Populärvetenskapling sammanfattning
Susan Lindecrantz | LTH
Investigation of flame emission and absorption spectroscopy using the
HITRAN/HITEMP database and simulations for concentration and
temperature determination in combustion environments Susan Lindecrantz @ May 2010 Lund University, Faculty of Engineering (LTH)
Division of Combustion Physics
Sweden
The aim of this work was to investigate the spectral infrared radiation properties from a flame or gas flow theoretically with help
of HITRAN/HITEMP database and compare with experimental measurements. The main focus in this study was molecular
species such as CO2, H2O, CO and hydrocarbon fuels. The ambition was to be able to simulate or describe the detailed spectroscopy of the infrared emission and absorption of hot gases mixtures. Based on the simulations, valuable information like
temperature, species concentrations can be extracted from either emission or absorption spectroscopy. A high resolution FTIR
emission spectrum from laminar methane/air premixed flame has been recorded, which will be used as a validation of the developed code for hot gas emission simulation.
1 Introduction
In today’s society, combustion is a large part of
the everyday life; more than 90% of the energy used
in the world is related to combustion [1]. The
combustion of fossil fuels leads to environmental
problems, e.g. air pollutants and global warming,
requires a better understanding of the processes
taking place in combustion. Combustion also plays a
big role in many industrial devices like engines and
requires industries to think about efficiency and
environmentally friendly combustion to be able to
compete on an international market. Many different
non-intrusive optical techniques for spectroscopic
diagnostics have been developed for measurements
of species concentrations and temperatures.
Within the field of flame spectroscopic studies
the infrared regions are of high interest because
important fuels like methane and combustion
products like CO2, CO and H2O are detectable in the
infrared region. Detection of species, within the
infrared region, for concentration measurements can
give an opportunity to better understand the
processes in an engine or a flame.
In previous master’s projects [2] it has been
stated that spectroscopic diagnostic techniques, e.g.
LIF (Laser-Induced Fluorescence) and Rayleigh
scattering, are mostly conduced in the ultraviolet and
visible region, in which molecules undergo
electronic transitions and thus have broad and
structure less distribution. Therefore the UV and
visible regions are not always optimal for
spectroscopic diagnostics since these species do not
have accessible transitions in those regions. In the
field of engine measurements, these methods require
not only optical access for observation and also an
additional opening for introduction of excitation
signal to the combustion chamber.
However, in the infrared regions can appear
with strong rotational or vibrational transitions,
forming bands and band-heads. The spectra from a
flame or a combustion chamber may be recorded
with line-of-sight absorption or thermal emission
spectroscopy. The main difficulties with diagnostics
in this region are line overlapping and spectral
interference [2].
Combustion based engines will remain
indispensable for many years, despite efforts in
introducing new energy sources; and thus urgently
need to be improved with regard to fuel efficiency
and pollutant emission. One promising approach to
reduce pollution emission is to dilute the air with
recirculated gases from the preceding ignition cycle,
so called internal exhaust gas recirculation (EGR).
But, in order to control and optimize this
complicated process, new high-speed diagnostic
techniques are needed to determine the amount of
recirculated gas in the engine, especially near the
spark plug, during intake and compression cycle by
monitoring water vapor or carbon dioxide. If one
can, with line-of-sight measurements determine the
concentration of the carbon dioxide just before the
ignition; it can be used to estimate the amount of
internal EGR.
2 Investigation and modelling of infra-red spectra in a flat flame The spectra from the premixed laminar burner were
reordered with a Fourier transform infrared
spectrometer. Fig. 1 illustrates the setup of the flame
measurement.
Fig. 1: Experimental setup for the flame experiment for
measurement on a methane/air laminar premixed flame.
Master of Science Thesis 99
LTH | Susan Lindecrantz
With help of a database containing molecular
parameters called HITRAN (T<1000K) and
HITEMP (T>1000K) a line-by-line radiation model
was created. With the assumption of no scattering
and homogeneous medium the radiative transfer is
simplified to Eq. (1). The solution of the question of
radiative transfer can then be obtained from Eq. (2)
used to calculate the absorption or emission.
vv
v
v SJd
dJ=+
τ (1)
[ ]vv eSeJlJ vvv
ττ −− −+= 1)0()( (2)
Assuming LTE the source function Sv is equal
to the Planck function Bv due to the Kirchhoff’s law.
The transmitted intensity at certain wavenumber,
Jv(l), be through a gas can be related to the incident
intensity, Jv(0), by the Beer-Lambert’s Law as stated
from the radiative transfer for the case of pure
absorption. This can be simulated using the
HITRAN or HITEMP database where the Beer’s law
given in Eq. (3) and the optical depth can be
calculated as Eq. (4).
veJ
lJ
v
v τ−=)0(
)( (3)
LfTSPxLk vvspeciesvv 0)( −==τ (4)
Here the kv [cm-1
] is the spectral absorption
coefficient, L is the optical path length of the
absorbing medium, xspecies is the mole fraction of the
absorbing species, P is the total pressure of the gas
mixture, S(T) is the line strength [cm-2
/atm] at the
temperature T [K] The line strengths are tabulated in
HITRAN with the unit [cm-1
/ molecules cm-2
] and
can be converted into [cm-2
/atm] in Eq. (5) at
reference point. Eq. (6) may then be used to correct
the line strength for the temperature. The line
strength has been transferred with help of Loschmidt
number at STP.
−−
−−
−
−=
)exp(1
)exp(1
)exp(
)exp(
)(
)()()(
2
2
2
2
refref
lower
lower
refref
ref
T
vc
T
vc
T
Ec
T
Ec
TQ
TQ
T
TTSTS
(5)
TcmmoleculescmSatmcmS
296102.68676)/()/( 19212 ⋅⋅⋅= −−−
(6) (2.15)
The fv-v0 [cm] is the normalized lineshape
function. Pressure changes and other perturbations
give rise to collision-broadened spectral lines. This
broadening is represented by the Lorentzian Eq. (6)
and has been used in these simulations. Although
different methods for giving approximations for the
Voigt line profile by Whitting [4] and another one is
given by Yuyan Liu [5], representing a combination
of Gaussian and Lorentzian, it was never verified.
The half-width-at-half-maximum has been calcul-
ated by Eq. (8).
22 )(
1
corrL
LL
vvf
−+=
γγ
π (7)
srefrefselfsrefrefair
n
ref
L pTpppTpT
TTp ),())(,(),( γγγ +−
= (8)
The p is the total pressure of the gas [atm],
temperature T [K] and partial pressure ps [atm] of
the gas. In this equation γair [cm-1
/atm] is the air-
broadened halfwidth at half maximum at Tref = 296
K and pref at 1 atm, γself [cm-1
/atm] is the self-
broadened halfwidth at half maximum and n is the
coefficient of temperature dependence of the air-
broadened halfwidth.
The spectra from the premixed flame was
recorded and processed to obtain the ‘true’ spectra
without the response function. The same setup was
used to measure a blackbody at temperature 1473.15
K.
Using the obtained response function the true
spectra for the premixed methane/air flame can be
determined. The resulting spectra for the two flames
are displayed in Fig. 2. The blackbody spectrum was
fitted to get rid of these absorption lines and then
expanded at lower wavenumbers since the
spectrometers sensitivity falls off in this area.
Fig. 3 shows this drop-off in which the sensi-
tivity seems to fall off rapidly around 1850 cm-1
.
This is consistent with the detector’s material
sensitivity curve for Insb which falls off drastically
after 5µm (2000 cm-1
).
Fig. 2: Shows the comparison between the different measured
locations of the flame spectra with φ = 0.8 and φ = 1.6.
2000 2500 3000 3500 4000 4500 5000 5500
0
1
2
3
4
5
6
x 10-4
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Measured spectra from a flame with phi =0.8
2000 2500 3000 3500 4000 4500 5000 5500
0
2
4
6
8
10
x 10-4
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
3 mm above the visible flamezone
1 mm above the visible flamezone
at the visible flamezone
at the visible flamezone
1 mm below the visible flamezone
3 mm below the visible flamezone
H2O + CO
2
H2O
H2O
CO
CO2
CO2
H2O + CO
2
H2O + CO
2
H2O + CO
2
CH4
CH4
CO
2000 2500 3000 3500 4000 4500 5000 5500
0
2
4
6
8
10
x 10-4
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Measured spectra from a flame with phi = 1.6
2000 2500 3000 3500 4000 4500 5000 5500
0
2
4
6
8
10
12
14
x 10-4
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
at the visible flamezone
1 mm below visible flamezone
3 mm below visible flamezone
3 mm above visible flamezone
1 mm above visible flamezone
at the visible flamezone
CH4 H
2O + CO
2
H2O + CO
2CH
4
H2O + CO
2
H2O + CO
2
CO
CO
CO2
CO2
CO
H2O
CO
H2O
100 Appendix D: Populärvetenskapling sammanfattning
Susan Lindecrantz | LTH
Fig. 3 shows some comparison between the
measured and the simulated spectra. The simulated
spectra have been simulated with the concentration
and temperature taken from the CHEMKIN
estimations for methane/air flame. There are notable
differences between the lean and the rich flame.
Fig. 3: Shows the comparison between the simulated spectra and
the measured spectra for the different locations above the flame
with φ = 0.8 and φ = 1.6.
The spectra for lean flame below the visible
flame zone shows less emission and contains more
static noise than the other spectra points for the same
flame. This apparent spectra noise could be
explained by the lower temperatures thus less
emission and the existence of fluid gas before the
reaction zone. For the spectra at the visible flame
zone the CO2 band becomes more apparent and there
is a CO band just becoming visible. The spectra
above the visible flame zone show very strong water
lines and CO2 band while the CO band no longer is
clearly visible in comparison, as shown in Fig. 3.
This is expected for the lean flame since according
to the CHEMKIN the CO is created near the visible
flame zone and then disappears afterwards as it is
transformed into CO2.
At the fundamental band of CO2 one can see
very strong absorption lines; this is the same for all
spectra.
There is a band structure from the CH4 that
has been identified around 3000 cm-1
. The CH4 band
seems to only exist at the visible flame zone for the
lean flame. There is no indication that this band exist
before the visible flame zone, possibly since the CH4
exists here as fluid gas and has not been heated
enough to produce emission bands. After the visible
flame zone this structure seems to have disappeared
again. Since in a lean flame there exists an excess of
oxygen, indicating that all fuel will have been
transferred into products after the visible flame zone.
The rich flame shows apparent emission
spectra for all measurements point except 3 mm
below the visible flame zone, indicating that the rich
flame is much hotter than the lean flame. It is also
possible that it has a much larger reaction zone or is
located earlier above the burner than the lean flame.
In the rich flame the CO bands emission are
very strong and stay strong even above the visible
flame zone, indicating that CO has survived into the
product zone. The CH4 band show a very clear band
structure for the lean flame at 1 mm below the
visible flame zone and shows a less clear band
structure at the visible flame zone in comparison,
indicating a decrease of the concentration of CH4.
1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500-1
0
1
2
3
4
5
6x 10
-5
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Comparison between measured and simulated spectra for phi = 0.8 at 3 mm below the visible flamezone
1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500-4
-2
0
2
4
6
8
10x 10
-5
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Comparison between measured and simulated spectra for phi = 1.6 at 3 mm below the visible flamezone
measured spectra
simulated spectra
measured spectra
simulated spectra
CO
H2O
H2O
H2O
H2O
CO2
CO2
1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500-2
0
2
4
6
8x 10
-5
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Comparison between measured and simulated spectra for phi = 0.8 at 1 mm below the visible flamezone
2000 2500 3000 3500 4000 4500 5000 5500
0
0.5
1
1.5
2
2.5
x 10-3
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Comparison between measured and simulated spectra for phi = 1.6 at 1 mm below the visible flamezone
measured spectra
simulated spectra
simulated spectra
measured spectra
H2O
CO
CO
CO
CO2
CO2
H2O
H2O
H2O
H2O
CH4
H2O + CO
2
2000 2500 3000 3500 4000 4500 5000 5500
0
0.5
1
1.5
2
2.5
x 10-3 Comparison between measured and simulated spectra for phi = 1.6 at visible flamezone
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
2000 2500 3000 3500 4000 4500 5000 5500
0
5
10
15
x 10-4
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Comparison between measured and simulated spectra for phi = 0.8 at visible flamezone
simulated spectra
measured spectra
simulated spectra
measured spectra
H2O + CO
2
H2O + CO
2
H2O + CO
2
H2O + CO
2
H2O
H2O CO
2
CO
CH4
CH4
CO2
CO2
CO
CO
2000 2500 3000 3500 4000 4500 5000 5500 6000
0
5
10
15
20
x 10-4
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Comparison between measured and simulated spectra for phi = 0.8 at 1 mm above the visible flamezone
2000 2500 3000 3500 4000 4500 5000 5500
0
0.5
1
1.5
2
2.5
x 10-3
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Comparison between measured and simulated spectra for phi = 1.6 at 1 mm above the visible flamezone
simulated spectra
measured spectra
simulated spectra
measured spectra
H2O + CO
2
H2O + CO
2
H2O + CO
2
H2O + CO
2CO2
CO2
H2O
H2O
CO
CO
2000 2500 3000 3500 4000 4500 5000 5500
0
0.5
1
1.5
2
2.5
x 10-3
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Comparison between measured and simulated spectra for phi = 0.8 at 3 mm above the visible flamezone
2000 2500 3000 3500 4000 4500 5000 5500
0
0.5
1
1.5
2
2.5
x 10-3
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Comparison between measured and simulated spectra for phi = 1.6 at 3 mm above the visible flamezone
simulated spectra
measured spectra
simulated spectra
measured spectraCO
2
CO2
H2O
H2O
H2O + CO
2
H2O + CO
2
H2O + CO
2
H2O + CO
2
CO
CO
Master of Science Thesis 101
LTH | Susan Lindecrantz
For the plots for 3 mm below the reaction zone
the two different flame spectra’s shows little
emission. Because of this the noise level of the
signal is very apparent and lays around 10-5
to 10-6
a.u. This noise level of the signal exists in all
spectra. The only difference is that it is more
prominent here due to the lower emission levels. For
the rich flame the CO band emerges around 2140
cm-1
from the cold flame structure, indicating that
CO is already formed here from the heat of the
reaction zone. Very little water lines are shown.
It can be noticed that in terms of line position
the simulated spectra fits overall well to the
measured, however the line strengths are sometimes
much bigger or smaller for the simulation for some
species and flame locations, see Fig. 4 for some
examples.
Uncertainties in the spectroscopic database
might be a source for the spectra’s fit not being
perfect. Uncertainty could be that the CHEMKIN
models a flame that is perfect laminar and adiabatic.
However in reality, the flame is not perfect adiabatic
since there will always be heat losses to the
environment. The burner has a stabilizer above the
flame which deviate the flame from perfect laminar.
This is especially true at the edges of the visible
flame zone, seen in Fig. 1. For example in the plot 1
mm above, for the rich flame, the CO band seem to
be missing in the simulation, while for the rich flame
this band is not seen in the measured nor the
simulated as expected. In the same plot the H2O
lines seem to be much bigger, however this could be
a result from partially absorption existing in the
band, see Fig. 4. The possible reason why some of
the lines seem to fit somewhat well and some are
partially or completely absorbed is because the
absorbing medium is cold and thus can only excite
certain populations in the molecules, the ground
state transitions. As given from the Boltzmann
distribution when the temperature increases higher
populations is occupied. This phenomenon is also
seen for the fundamental band of CO2.
Fig. 4: Shows the four examples of features in comparison
between the flame spectra for 1 mm above the visible flame zone
for φ = 0.8 and φ = 1.6. In the first upper image shows the combination band of H2O in which some lines have been
absorbed. The lower image shows part of the combination band of
H2O. The second upper image shows the band head of the fundamental CO2 (to the right) and the CO2 absorption lines (to
the left). The lower image shows part of the combination band of
H2O.
For the simulated spectra of 3 mm below the
visible flame zone in both flames shows very little
agreement with the simulated spectra. This is
because we do not have much emission in this
region and very low measured temperature and
concentrations in the simulations. For the plots in the
visible flame zone the CO seem to be
underestimated for both lean and rich flame. The
only plot that has visible CO band in the simulation
is the 1 mm below the visible flame zone for the rich
flame, and it is seem to be bigger than the measured
CO band. This is an indication that the either the
temperature or the concentration is not accurate with
the measurement for some species like CO.
The simulation was based upon the given
mole fractions and the temperature calculated from
the program CHEMKIN. It is clear from the
measurement and the simulated emission that some
lines should been more prominent but is in the
simulation too weak to be comparable with the CO2
band and water lines, especially true for higher
temperatures. A possibility is that the CHEMKIN
was provided with too low concentrations or
incorrect temperatures to give a perfect fit. Another
possibility is that since the simulations with over
1000K has been simulated with HITEMP95 lines
can be missing in the database for CO, CO2 and
H2O. Most of the H2O and the CO2 lines seem to be
weaker since there is absorption. It is difficult to
determine if it is a good fit or not, due to the large
amount of absorption in the fundamental band of the
CO2 and the combination band of H2O. The species
of N2 and O2 is too small in comparison with the
other features that they do not appear together with
the other species.
3 Conclusion and outlook In this investigation high resolution spectra
of a premixed laminar burner for a lean and a rich
flame at different locations above the burner are
studied. With help of these spectra a simulation code
3670 3672 3674 3676 3678 3680 3682 3684 3686 3688
0
2
4
6
8
10
12
x 10-4
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Example of comparison between measured and simulated spectra for phi = 0.8 at 1 mm above the visible flamezone
3500 3505 3510 3515
0
5
10
15
x 10-4
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
simulated spectra
measured spectra
simulated spectra
measured spectra
Example of comparison between measured and simulated spectra for phi = 1.6 at 1 mm above the visible flamezone
2380 2381 2382 2383 2384 2385 2386 2387 2388 2389
0
0.5
1
1.5
2
x 10-3
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Example of comparison between measured and simulated spectra for phi = 0.8 at 1 mm above the visible flamezone
3475 3480 3485 34900
0.5
1
1.5
2
x 10-3
Wavenumber [ cm-1 ]
Intensity [ a.u. ]
Example of comparison between measured and simulated spectra for phi = 1.6 at 1 mm above the visible flamezone
simulated spectra
measured spectra
simulated spectra
measured spectra
102 Appendix D: Populärvetenskapling sammanfattning
Susan Lindecrantz | LTH
for generating emission was created. The different
approaches were studied in order to obtain
information about the temperature or concentration
from a gas in an engine just before combustion, with
the aim of finding ways to be able to estimate the
internal EGR by the CO2 concentration.
From the CHEMKIN simulation, six species
were chosen to be studied since they are assumed to
be the main contributors of the combustion of CH4
and C8H18. From the flame investigation, it is clear
that the HITRAN and HITEMP database provides
with important spectroscopic data for the infrared
region. It has shown to be easy to use and a good
tool to for simulating spectra in MATLAB, in terms
of line identification and simulation, provided that
there is no absorption from the surrounding.
Absorption from air is a huge factor when
measuring emission, since it absorbs at the regions
of interest; the fundamental band of CO2 and the
first combination band of H2O. To simulate the
intensity it is essential to know the temperature and
the mole fractions of the investigated species. This
creates a problem since the two are often not known.
In this study, an initial estimation of the mole
fraction from the reaction formulas was made to
give an initial estimation in the engine simulations.
Different methods have been studied to extract this
information with either emission or absorption
methods.
In this initial investigation certain
assumptions have been made. The scattering effect
is assumed to be negligible. In further investigation,
the scattering effect should be more closely
investigated, especially if there are particles in the
system. Then the radiative transfer becomes
dependent on the extinction from absorption and
scattering, see Eq. (9).
For the emission measurement, air absorp-
tion can be avoided by using fibers between the
window of the engine chamber and the detector. For
the engine measurement, one might have to consider
the radiative emission from the walls of the
combustion chamber and the spark plug. The
emission from the heated walls and spark plug might
also be captured by the detector and be a source of
error. If it is large enough, compared to the spectral
features of interest, it needs either to be subtracted or
accounted for in the simulation. If it’s small enough,
it can be neglected. The temperature of the walls in
the engine should be much lower than the actual gas
inside the chamber. If that is the case then the wall
should give rise to a lower blackbody radiation
curve contribution. However since this engine has
two opposite windows this effect can be assumed to
be reliable. The spark plug has been blocked in the
line-of-sight measurement. Due to this these
contributions have been assumed in this initial study
to be insignificant.
If the emission spectra could be obtained
from a FTIR spectrometer, emission simulations
could be made to obtain a best fit of the simulated
and measured spectra. By study of these spectra, the
information about the temperature and then the
concentration can be made. The next step would
then be to use the emission ratio of two single lines
of the same species to obtain the concentration. As
stated before the emission depends linearly on the
concentration for optically thin lines, hence the Eq. Eq. (10) then simplifies to the Planck function times
the optical depth,
[ ] vvvv BeBlJ v ττ =−= −1)(
With the upcoming new release of the
HITEMP database, more precise and extended
simulations can be made for high temperature
spectra. The next step could be to create a program
which can simulate the emission, the optical depth
and hence the transmission and absorbance with a
simple click. This could be very useful for students
and researchers alike.
Experiments to test the possibility of deter-
mining the temperature and the concentration from
the simulations were not conducted in this work, but
can be considered for future investigations.
4 Reference [1]
Bood, J. (2009) Introduction to combustion, Lecture material
in Laser-based combustion diagnostics.
[2] Pettersson, A. (2004) Investigation of infrared chemilumine- scence emission from laboratory flames, Master of Science
Thesis LTH, Division of Combustion, Lund University, p7.
[3] Zhou, X. et. al. (2005) Development
of a fast temperature sensor for combustion gases using a
single tunable diode laser, Appl. Phys. B 82, pp711-722.
[4] Witting, E. (1968) Quant. Spectrosc. Radiat. Transfer 8, p1379
[5] Liu, Y et. al. (2001) Simple empirical analytical approximati-
on to the Voight profile, Optical Society of America, pp711-722
[6] Farooq, A. et. al. (2008) In situ combustion measurements of
H2O and temperature near 2.5µm using tunable diode laser absorption, IOP publishing,, Meas Sci. Technol. 19, pp1-11