Molecular Transport Effects of Hydrocarbon Addition on Turbulent Hydrogen Flame Propagation
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Transcript of Molecular Transport Effects of Hydrocarbon Addition on Turbulent Hydrogen Flame Propagation
SM(1)11-13 Sep 20072nd International Conference on Hydrogen Safety, San Sebastian, Spain
Molecular Transport Effects of HydrocarbonAddition on Turbulent Hydrogen Flame Propagation
Siva P R Muppala and Jennifer X WenFire and Explosion Research Group, Department of Mechanical Engineering
Kingston University, London, UK
Naresh K AluriGas Turbine Combustion group, ALSTOM (Baden), Switzerland
F DinkelackerInstitut Fluid- und Thermodynamik, Universität Siegen,
Paul-Bonatz-Str. 9-11, 57076 Siegen, Germany.
ThVSIEGENThVSIEGEN
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Contents
1. Motivation2. Flames previously investigated3. Molecular transport effects in premixed turbulent
combustion4. Outwardly propagating spherical flames5. Various approaches to modelling of H2+HC flames
6. Algebraic flame surface wrinkling model 7. Results8. Conclusion
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Study:
Influence of molecular transport (preferential diffusion and Lewis number) effects in H2+HC mixtures
Quantitative evaluation of flame speed for mixed fuels
Motivation:
Safety considerations in hydrogen usage
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Hydrocarbon flames previously investigated
Flame
configurations
Effects investigated
Approach Experimental
source
Bunsen Burner
High-Pressure,
Fuel Type RANS, LES
Swirl Burner
High-Pressure,
Fuel Type RANS
Dump Combustor High-Pressure RANS, LES
Swirl Burner
Flame Stability & Dynamics RANS, LES
Bunsen Burner
High-pressure,
H2-doping RANS, LES
Tohoku University
University of Orleans
Different configurations studied numerically using the Algebraic Flame Surface Wrinkling Premixed Turbulent model
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Modelling Turbulent Premixed Combustion
lnE
k
ln k
lnE
k
ln k
/ Pressure:
Fine scale structures that can wrinkle the flame decreases
t xRe u l /
Fuel Variation (Lewis Number)
min or
Thermal DiffusivityLe
Mass Diffusivity D
0 75.k x tl / Re
Products
Reactants: Fuel + Air
Reaction zonePreheat zone
Le<1 Le=1 Le>1
Dminor
Dminor
Dminor
Molecular Transport Effects
Aluri NK, Doctoral Dissertation, University of Siegen 2007
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Flame Curvature, Mass Flow & Turbulent Flame Speed
Reaction Sheet
Burned
Unburned
A
A'
C
B'
B
Stream Lines
To Convex Flamelet toward the Burned Mixture
To Convex Flamelet toward the UnBurned Mixture
Unburned gas consumed by a
turbulent flamelet
1. Premixed gas flows along marked streamlines
2. Streamlines ┴ to flamefront
3. Ratio of mass flow flowing into the convex ‘BC unburned‘ / to convex ‘AC burned‘ ~ 3:1
4. The convex part of flamelet towards the unburned mix. affects the turbulent flame speed predominantly
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:Stream L ine
:H igher D iffusive R eactant; D
:L ower D iffusive R eactant; D
R eactionSheet
B urned
U nburned
h
l
D R ichD P oor
h
l
D P oorD R ich
h
l
(F uel/O /N )2 2
I n the case of C H or H - mixtures,
F uel is D and O is D .h
4
l
2
2
2I n the case of C H or C H - mixtures,
F uel is D and O is D .h
6
l 2
83
Preferential Diffusion and Lewis number Effects
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Outwardly Propagating Spherical flames – Kido database
Measured data:SL= Mean local burning velocity; = f(PD=Df/Do)
ST = Turbulent flame speed
H2/O2/N2; =1.2; Le=1.29 =0.8; Le=0.42
SL0=25cm/s
Le decrease
u’/SL0=1.4
Spherical gaseous (H2) explosion
Mixture data:Hydrogen-methane & Hydrogen-propane lean mixturesEquivalence ratio: 0.8Turbulent velocity = 2 m/s (max)
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DNS by Trouvé and Poinsot 1994 on lean H2/O2/N2 flames………………………………..
…………………………………………………… and DNS of lean H2 flame by Bell et al. 2006 (not depicted here), confirm the Le influence on turbulent flame speed, especially in lean H2 mixtures
This substantial rise in flame speed may be due to sum of DL and PDT effects, or, can also be explained using Leading Point concept
Lewis Number Effects – DNS investigations
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Modelling approaches to multi-fuel premixed turbulent flames
Weakly stretchedflamelet modelsbased on Ma
AnalyticalMethods(a submodelfor preferentialdiffusion effect)
Based onexp’taldata
Critically curvedflamelets imposedon flame-ballconcept byZel’dovich
exponential (Le-1) relation
Submodel for
time scale
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Weakly stretched flamelets concepts
SL= SL0(1 – Ma ּ sּ(c)
SL= stretched laminar flame speed substituted for SL0
Ma = Markstein number = f(flame stretch, curvature)
s�ּc is commonly simplified to Ka.Ma or Ka.Le
s is stretch rate Chemical time scale ּc = laminar flame thickness/
(unstretched laminar flame speed)2
Measured Ma for CH4- and H2-air mixtures for =0.40, 0.43 and 0.50 are 0.7 and -0.3, respectively. Bechtold and Matalon Combust. Flame 1999
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Analytical method – A submodel for preferential diffusion effect
0
0
0 0
(1 ) 1, if 1
(1 ), if 1
1 (1 )
stlp lp
st
stlp lp
st st
C d d
d C
C d
C C d
SL(lp) = Mean local burning velocity at the leading point of the flamelet, substituted for SL0 in the turbulent flame speed model
lp is (1/ local equivalence ratio) at the leading point
stC mass stoichiometric coefficient
0 1/Initial equivalence ratio/f od D D = ratio of diffusivities
of fuel and oxidant
Kuznetsov, V.R., and Sabel'nikov, V.A., Turbulence and Combustion, Hemisphere, 1990.
Assumption: DO,u = u
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Critically curved flamelets: flame-ball concept by Zel'dovich
Asymptotically (activation temp ∞) exact solution of stationary 1D balance equations for the temperature and mass fraction of the deficient reactant, for single-step single-reactant chemistry.
For Lewis numbers < 1, the flame ball temperature is given by
r u b uT T T T Le
1.5
1
0
exp2
cr b b rcr c c
L r b r
R T T TLe
T T T
0
exp( 1)cr
c
Le
The chemical time scale for the highest local burning rate is
0.25 0.2
0.8 0.20
0 0
0.461
exp( 1)t
T L Loc
pS S u S
Le p
Lipatnikov and Chomiak., Prog. in Energy, Comb Sci 2005Aluri, Muppala, Dinkelacker Comb Flame 2006
Muppala et al. Comb Flame 2005
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Premixed Turbulent Combustion submodel
c u Lw s General reaction rate expression
Folding factor = Flame surface area / Volume
A
AT
Fuel+Air
T
T
cA
A
A
A
Turbulent flame surface area
Averaged flame surface area
(Re , , ,...)tT f u p
A
A
Muppala, Aluri, Dinkelacker -- Comb Flame 2005Aluri, Pantangi, Muppala,, Dinkelacker – Flow, Turb Comb 2005
Surface density functionc
~T T
L
A s
A s
0.
1
3
0
0.2
0.25
AlgebraicFlameSurfaceWrinkling(AFSW)Model
0.46 '1 e
eR
L t
Le
T T
L
A s u
A s s
because of Damköhlerhypothesis
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{without the Lewis number effect}
{without Preferential Diffusion effect}
Model predictions
0.3
0.250
0
0.461 Re
exp( 1)T L tL
uS S
Le s
0.3
0.251 0.46ReT L tL
uS S
s
Algebraic Flame Surface Wrinkling model: two forms
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0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2
Exp_00Model_00
ST,
m/s
u', m/s
Le = 0.38
100%H2-0% CH4
0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2
Exp_05Model_05
ST,
m/s
u', m/s
Le = 0.40
50%H2-50% CH4
0
0.5
1
1.5
2
0 0.5 1 1.5 2
Exp_10
Model_10
ST,
m/s
u', m/s
Le = 0.890%H2-100% CH4
Turbulent flame speed vs. turbulence intensity for lean CH4–H2 flames. Model predictions based on SL0.
Results1 – Hydrocarbon + Hydrogen mixtures: CH4 + H2
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0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2
Exp_00Model_00_SLModel_00_SL0_Le
ST,
m/s
u', m/s
Le = 0.38
100%H2-0% CH4
0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2
Exp_05Model_05_SLModel_05_SL0_Le
ST,
m/s
u', m/s
Le = 0.4050%H2-50% CH4
0
0.5
1
1.5
2
0 0.5 1 1.5 2
Exp_10Model_10_SLModel_10_SL0_Le
ST,
m/s
u', m/s
Le = 0.89
0%H2-100% CH4
CH4–H2 mixtures. Model predictions are based on SL (mean local burning velocity with preferential diffusion) and Lewis number effect.
Results2 – Hydrocarbon + Hydrogen mixtures: CH4 + H2
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0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2
Exp_00Model_00
ST,
m/s
u', m/s
100%H2-0% C3H8
0
0.5
1
1.5
2
0 0.5 1 1.5 2
Exp_05Model_05
ST,
m/s
u', m/s
50%H2-50% C3H8Le = 0.42 Le = 0.70
0
0.5
1
1.5
0 0.5 1 1.5 2
Exp_10
Model_10
ST,
m/s
u', m/s
0%H2-100% C3H8Le = 1.57
Turbulent flame speed vs. turbulence intensity u’ for lean C3H8–H2 flames. Model predictions based on SL0.
Results1 – Hydrocarbon + Hydrogen mixtures: C3H8 + H2
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0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2
Exp_00Model_00_SLModel_00_SL0_Le
ST,
m/s
u', m/s
Le = 0.42100%H2-0% C3H8
0
0.5
1
1.5
2
0 0.5 1 1.5 2
Exp_05Model_05_SLModel_05_SL0_Le
ST,
m/s
u', m/s
Le = 0.7050%H2-50% C3H8
0
0.5
1
1.5
0 0.5 1 1.5 2
Exp_10Model_10_SLModel_10_SL0_Le
ST,
m/s
u', m/s
Le = 1.570%H2-100% C3H8
C3H8–H2 mixtures. Model predictions are based on SL (mean local burning velocity with preferential diffusion) and Lewis number effect.
Results2 – Hydrocarbon + Hydrogen mixtures: C3H8 + H2
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0
1
2
3
4
5
6
0 1 2 3 4 5 6
ST/S
L - M
odel
ST/SL - Exp
H2 doped with CH4
01234567
0 1 2 3 4 5 6 7
H2 doped with C3H8
ST/S
L - M
odel
ST/SL - Exp
Correlation plot for turbulent flame speed ST : Experimentally measured vs. model predicted, estimated based on SL for CH4–H2 and C3H8–H2 mixtures.
Correlation plots – turbulent flame speed: Exp vs. Model
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An existing algebraic flame surface wrinkling reaction model was used to investigate the quantitative dependence of turbulent flame speed on molecular transport coefficients for two-component lean fuel (CH4–H2 and C3H8–H2) mixtures.
The model predictions were in good quantitative agreement with the corresponding experiments, if either mean local burning velocity SL or an exponential Lewis number term of the fuel mixture is used in the reaction model. The latter approach is a generalisation of earlier findings for single fuels and shows the applicability of the exponential Le term for dual-fuel mixtures.
The hydrocarbon substitutions to H2 mixtures are expected to suppress the leading flame edges, which are manifested by a decrease in mean local burning velocity, eventually preventing transition to detonation. Addition of hydrocarbons may also promote flame front stability of lean turbulent premixed H2 flames.
Summary
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