Spark Ignition Engine Combustion - İTÜweb.itu.edu.tr/~sorusbay/SI/LN01.pdf · Spark Ignition...
Transcript of Spark Ignition Engine Combustion - İTÜweb.itu.edu.tr/~sorusbay/SI/LN01.pdf · Spark Ignition...
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Istanbul Technical University - Automotive Laboratories
Spark Ignition Engine Combustion
MAK 652E
Introduction to Combustion Process in Engines
Prof.Dr. Cem Soruşbay
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Contents
Course information
Combustion process in engines
Classification of engines
Conventional engines
Advance concepts in engine combustion
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Information
Prof.Dr. Cem Soruşbayİ.T.Ü. Makina Fakültesi Otomotiv LaboratuvarıAyazağa Yerleşkesi, Maslak – 34469 İstanbul
Tel. 212 – 285 3466 [email protected]
http://web.itu.edu.tr /sorusbay/SI/SI.htm
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Course Plan
Introduction to engine combustion process
Premixed combustion in engines
Stratified charge engines, lean combustion, cyclic variations
Combustion modelling in engines, thermodynamic models
Multidimensional modelling of SI engines
Chemical kinetics of HC combustion
Autoignition in engines, knock modelling
Exhaust emissions, kinetics of pollutant formation
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Assessment Criteria
Midterm examinations 2 x 15 = 30 %
16th March, 2017
27th April, 2017
Project 20 % to be submitted by 11th May, 2017
Final examination 50 %
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
References
Soruşbay, C., Lecture Notes, İ.T.Ü., 2010 (Power Point presentation)
Soruşbay, C. et al., İçten Yanmalı Motorlar, Birsen Yayınevi, İstanbul, 1995.
Pulkrabek, W.W., Engineering Fundamentals of the Internal Combustion Engine, Prentice Hall, New Jersey, 1997.
Mattavi, J.N. And Amann, C.A. (Eds.), Combustion Modelling in Reciprocating Engines, Plenum Press, New York, 1980
Ramos, J.I., Internal Combustion Engine Modelling, Hemisphere Publishing Corp. New York, 1989.
Turns, S.R., An Introduction to Combustion - Concepts and Applications, Mc Graw - Hill, New York, 1996.
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
References
Merker, G.P. et al., Simulating Combustion, Springer Verlag, Berlin, 2006.
Heywood, J.B., Internal Combustion Engine Fundamentals, McGraw Hill Book Company, New York, 1988.
Weaving, J.H., Internal Combustion Engineering : Science and Technology, Elsevier Applied Science, London, 1990.
Stone, R., Introduction to Internal Combustion Engines, Macmillan, London, 1994.
Arcoumanis, C and Kamimoto, T., Flow and Combustion in Reciprocating Engines, Springer Verlag, Berlin, 2009.
Other references given in the list (see web page of the course)
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Combustion Process in Engines
Internal Combustion Engines (IC-engines) produce mechanical power from the chemical energy contained in the fuel, as a result of the combustion process occuring inside the engine
IC engine converts chemical energy of the fuel into mechanical energy, usually made available on a rotating output shaft.
Chemical energy of the fuel is first converted to thermal energy by means of combustion or oxidation with air inside the engine, raising the T and p of the gases within the combustion chamber.
The high-pressure gas then expands and by mechanical mechanisms rotates the crankshaft, which is the output of the engine.
Crankshaft is connected to a transmission/power-train to transmit the rotating mechanical energy to drive a vehicle.
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Combustion Process in Engines
Most of the internal combustion engines are
reciprocating engines with a piston that reciprocate
back and forth in the cylinder.
Combustion process takes place in the cylinder.
There are also rotary engines
In external combustion engines,
the combustion process takes place outside
the mechanical engine system
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Energy Conversion
(Merker et.al, 2006)
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Energy Conversion
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Classification of Engines
Method of ignition
Spark Ignition (SI) engines,
ignition is by the application of external energy (to spark plug) mixture is uniform (conventional engines), mixture is non-uniform (stratified-charge engines)
Compression Ignition (CI) engines,
ignition by compression in conventional engine (Diesel engine), pilot injection of fuel in gas engines (eg, natural gas and diesel fuel –> dual fuel engines)
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
GDI Engines
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
History of Engines
Huygens (1673) developed piston mechanismHautefeuille (1676) first concept of internal combustion enginePapin (1695) first to use steam in piston mechaanism
“Modern” engines using same principles of operation as present engines – previously no compression cycle
Lenoir (1860) driving the piston by the expansion of burning products - first practical engine, 0.5 hp, mech efficiency up to 5%
Rochas (1862) four-stroke concept was proposedOtto – Langen (1867) produced various engines, 11% efficiency
Otto (1876) Four-stroke engine prototype built, 8 hpClark (1878) Two-stroke engine was developedDiesel (1892) Single cylinder, compression ignition engine
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
History of Engines
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Otto Cycle
Otto cycle (heat addition at constant-volume)2
3 p
p
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Diesel Cycle
cut-off ratio
(load ratio)
Diesel cycle (heat addition at constant-pressure)
2
3
V
V
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Comparison of Ideal Cyles
Otto cycle
Diesel cycle
Dual cycle
1
11
kOttoth
)1(
1
11
1
k
k
kDieselth
)1( 1
1
11
1
k
k
kDualth
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Comparison of Ideal Cycles
For > 1 and k > 1
term is greater than 1
therefore t-otto > t-dies for a constant value of compression ratio
Also t-otto > t-dual > t-diesel
efficiency of Dual cycle lies between Otto and Diesel cycles according to the value of
)1(
1
k
k
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Comparison of Engines
In real engines,
SI engines have a compression ratio between 10:1 to 12:1
this value is limited due to engine knock
CI engines have compression ratio higher than 14:1 to provide temperature and pressure required for self ignition of the fuel
compression ratio of 16:1 to 18:1 is sufficient for efficiency, but used for improving ignition quality
high compression ratio increases thermal and mechanical stresses
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Comparison of Engines
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
SI Engines
a) Full load b) Part load
SI engine losses at full load (WOT) and part load
(Merker et.al, 2006)
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
SI Engines
a) Full loadb) Part load
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
SI Engines
Engine map with lines of constant fuel consumption
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Losses in Real Engine
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Losses in Real Engine
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Conventional Diesel Engines
Phases of combustion process in a Diesel engine,Ignition delay periodPremixed combustion phaseMixing-controlled combustion phaseLate combustion phase
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Conventional Diesel Engine
Conventional Diesel engine combustion
Temporal trajectories of equivalence ratio () and temperature
for injection timing of 25, 15 and 5 oCA BTDC
Eq
uiv
ale
nce
ra
tio
Temperature
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Conventional Diesel Engine
Vibe parameter
(Mehdiyev, 2008)
m = 1.95“M” engine
m = 1.2“MR” process
m = 0.65CR injection
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
NOx – PM Trade-off
00 1 2 3 4 5 6 NOx7
0.05
0.10
0.15
0.20
g/kWh
Euro II (10/95)
Euro III (10/00)Soot
Euro IVEuro V
State ofthe art
Low swirl combustionelevated injection pressureinjection rate shapingpartly EGR
+ cooled EGRpart.-trap
NOX-cat.part.-trap
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
NOx – PM Trade-off Curve
NOx vs. Soot Trade-Off
0,20
0,40
0,60
0,80
1,00
1,20
1,40
100 150 200 250 300 350 400 450
NOx [g/h]
So
ot
[g/h
]
map=200 kPA AA9
map=200 kPA AA3
map=180 kPA AA9
map=180 kPA AA3
map=160 kPA AA9
map=160 kPA AA3
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
NOx – PM Trade-off
PIMIPol
Pilot injectionMain injectionPost Injection
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
NOx – PM Trade-off Curve
(Sorusbay et al., Int J Vehicle Design, 2007)
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Split Injection Strategies
MAIN INJECTION
PRE INJECTION +MAIN INJECTION
PRE INJECTION +SPLIT MAIN INJECTION
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Operating Regions in Relation to NOx and PM
Emissions of NOx and PM
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Operating Regions in Relation to NOx and PM
Emissions of NOx and PM at various load conditions
(Akihama, SAE 2001-01-0655)
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Limitations for SI Engines
(Source : Morey, 2011)
Compression and
Combustion
Friction Loss
Heat Loss
Incomplete oxidation
Slow burning
Knock limit
Efficiency limited by CR
Gas Exchange Process
Heat Loss
Pumping Losses
Waste heat out Exhaust
Inefficient valve timing
at varying speeds
Limitations for CI Engines
Major limitations with Diesel engines today
Controlling NOx and PM emissions
Reducing fuel consumption, CO2 emissions
Real-World exhaust emissions
PEMS
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Real-World Exhaust Emissions
(Source : International Council on Clean
Transportation, 2015)
Advanced Combustion Concepts
Compression Ignition (CI) engines have higherefficiency at part load operation, longer lifetime andrelatively lower emissions of CO2, CO and unburned HC
Spark Ignition (SI) engines have higher powerdensity and lower combustion noise.
In the history of engine design and development, there have been many attempts to combine theadvantages of both CI and SI engines.
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Gasoline Direct Injection Engines
Conventional Spark Ignition Engines
pre-mixed combustion
homogeneous and stoichiometric
mixture prepared in the manifold
GDI Engines
in-cylinder mixture formation
stratified charge with a globally
lean mixture
Spray guided GDI Engine
Gasoline Direct Injection Engines
(Source : Freeland et al., FISITA, 2013)
NEDC test Residency Points
shift up for
downsized GDI engine
o 2.4 liter , V6 engine
• 1.2 liter , I3 engine
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Advanced Combustion Concepts
(Source : Ulas, PhD Thesis, TU Eindhoven, 2013)
Low Temperature Combustion
(Source : Wagner, SAE Paper No.2003-01-0262)
Heavy EGR application
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HCCI Engines
Homogeneous Charge Compression Ignition engines : lean and homogeneous mixture is compressed until p and T are high enough for autoignition to ocur
HCCI ignition is governed by chemical kinetics andhistories of cylinder pressure and temperature (inlet air temperature, compression ratio, residual gas ratio andEGR, wall temperature). Combustion starts simultaneouslyall over the cylinder
Reaction rate is much lower than knock in SI engines due toa higher dilution of the fuel with air or residual gases (EGR)
HCCI Engines
High thermal efficiency due to high compression ratio, rapid heat release rate
Low specific fuel consumption with lean mixture
Low NOx emissions
Difficulties in controlling ignition and combustion over a wide range of engine operating conditions
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Diesel and HCCI Engines
Comparison between conventional Diesel engine and HCCI engine
Longer induction time for HCCI and lower cylinder temperatures
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
HCCI Engines
Homogeneous Change Compression Ignition engines have features from both SI and CI engines;
Lean and homogeneous mixture is compressed until p and T are high enough for autoignition to occur
Combustion starts simultaneously all over the cylinder
Reaction rate is much lower than knock in SI engines due to a higher dilution of the fuel with air or residual gases (EGR)
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
HCCI Engines
Autoignition process is controlled by time history of p and T during intake and compression stroke
autoignition is mainly governed by the H (hydrogen), OH (hydroxyl), H2O2 (hydrogen peroxide) and HO2 (hydroperoxyl) radicals
H2O2 and HO2 concentrations increase progressively during compression as p and T increases
These two radicals also govern low temperature reactions (LTR), or cool flame
At temperatures between 1050 and 1100 K, H2O2 decomposes and forms OH that quickly reacts with fuel molecules to produce heat and water -> autoignition starts -> high temperature reactions (HTR)take placeconcentration of H and OH radicals inc rapidly, while H2O2 concentration drops
(Manente, V., PhD Thesis, Lund University, 2007)
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
HCCI Engines
Change of mole fractions
OH (hydroxyl),
H2O2 (hydrogen peroxide) , HO2 (hydroperoxyl) radicals
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
HCCI Engines
Autoignition temperature is controlled by the fuel used
it is between 1050 – 1100 K for fuels with no LTR
such as natural gas, iso-octane, gasoline with high aromatics
fuels with LTR, it is between 920 – 950 K
gasoline with high paraffin content, fuels containing n-heptane
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Advantages vs Disadvantages
HCCI combustion has fast burning rateclose to ideal Otto Cycle (higher thermal efficiency than Diesel cycle)
lower fuel consumption (low CO2 emissions) compared to SI and CI engines of a given output power and CR
lower pumping losses compared to SI engines at part load (no throttle), but CI engines have higher part load efficiency
HCCI engines operate lean (with T below 1900 K) and due to fast combustion residence time of nitrogen at T higher than 2000 K is very short
Fast burning results in high pressure rise ratenoise emissions, structural damagesdifficult to control combustion phasing, ignition relies on spontaneous autoignition
Low temperature combustion inc HC emissions from the engine
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
HCCI Engines
Soot formation region is with equivalence ratio above 2 and temperature between 1700 – 2500 K
Thermal NOx formation region is with equivalence ration below 2 and combustion temperature above 2000 K
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Controlling HCCI Engines
HCCI ignition is governed by chemical kinetics of mixture and histories of p and T in combustion chamber
Controlling combustion and ignition;
In-cylinder temperature
inlet air temperature
compression ratio
residual gas ratio and EGR
wall temperature, cooling water temperature, wall deposits
Air-fuel chemistry
dual fuel injection system (fuels with different ignition tendancies)
Mixture composition
fuel stratification in direct injection
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Diesel and HCCI Engines
solid lines : HCCI
dotted lines : Diesel
(Aceves et al.
SAE 2001-01-2077)
Performance map for Volkswagen TDI 4-cyclinder engineHCCI engine is more efficient at low torque at any speedHigher efficiency is due to faster combustion
(approaching to ideal Otto cycle)
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Diesel and HCCI Engines
Performance map for Volkswagen TDI 4-cyclinder engine
HCCI engine has,
72% of max torque obtained by Diesel
88% of the power obtained by Diesel
while producing practically no PM and less than 100 ppm NOx
under all operating conditions
Needs no delay to reduce NOx
Simulation results by Aceves et al., (SAE 2001-01-2077)
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Gasoline and HCCI Engines
Saab SVC, VCR, HCCI, =10:1 - 30:1
General Motors L850, HCCI, =18:1 - SI, =18:1, ( =9.5:1 std)
Scania D12 Heavy duty diesel engine, HCCI, =18:1
Fuel: US regular Gasoline
(Johansson, Lund University, 2009)
SI engine
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
HCCI Engines
Wiebe (Vibe) function
Double - Wiebe function
(Yasar et al., Appl Thermal Engineering, 2008)
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
HCCI Engines
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
HCCI Engines
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
HCCI Engines
PCCI Engines
Premixed charge compression ignition engines : mixture of the fuel with air is provided prior to theinitiation of combustion due to early injection of the fuelinto the cylinder at low pressure and temperatureconditions for autoignition to take place.
Combustion is controlled by chemical kinetics. Incylinder temperature levels are controlled by applyingheavy exhaust gas recirculation (EGR) rates to dominateignition process, which also controls NOx and PM emissions.
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PCCI Engines
Misfire especially at low load conditions is a potential problem
Rapid pressure rise at high loads and uncontrolledignition timing are other issues which can cause lowthermal efficieny and engine damage
Dual Fuel Combustion
Premixed Natural Gas induced into the cylinder duringthe intake stroke and ignited by pilot injection of Diesel Fuel
Lean operation is possible providing reduction in emissions and improvement in fuel consumption
City Bus fleet in Istanbul(1992)
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RCCI Engines
Reactivity Controlled Compression Ignition engine : mixtureis formed with early injection of the fuel into the cylinder
Low octane fuel injected earlier can
be blended with high octane fuel with
post injection
Fuel blend ratio and injection timing
are the parameters for control
(Source : Reitz, 2011)
RCCI Engines
Varying the mixture ratio of fuel blends with differentreactivity levels can provide considerably high thermalefficiencies.
Relatively low injection pressures, in comparison to fuelinjection systems used in modern diesel engines, provideenergy saving.
Low temperature combustion reduce NOx emissionswhile the level of uniformaty of the mixture reduce PM emissions.
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Advanced Combustion Systems
Injection timing and ignition
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Advanced Combustion Systems
HCCI homogeneous charge compression ignition
UNIBUS uniform bulky combustion system
PCCI premixed change compression ignition
PREDIC premixed lean diesel combustion
MK modulated kinetics
LTRC low temperature rich combustion
PCI premixed charge ignition
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Modulated Kinetics
Basic MK concept,
low temperature, premixed combustion system aimed at simultaneously reducing NOx and PM emissions (in a Diesel engine)
Low T can be obtained by heavy EGR reducing O2 concentration
-> but reduced O2 concentration increases PM in diffusion combustion
Fuel and air is mixed before combustion,
fuel injection time is retarded so that ignition delay is prolonged
(Kimura et al., SAE 1999-01-3681)
Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories
Modulated Kinetics
(Kimura et al., SAE 2001-01-0200)
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Prof.Dr. Cem SORUŞBAY - ITU Automotive Laboratories