Modeling Combustion in Spark-Ignition Engines Using G-equation Model with Detailed Chemistry
description
Transcript of Modeling Combustion in Spark-Ignition Engines Using G-equation Model with Detailed Chemistry
University of Wisconsin Engine Research Center
Modeling Combustion in Spark-Ignition Engines Using
G-equation Model with Detailed ChemistryLong Liang & Prof. Rolf D. Reitz
Acknowledgement: Ford Motor Company
PFI/DI-SI Engine
• CO Oxidation, H2-O2 reactions
• Pollutant formation
• G-equation description of combustion
• Laminar and turbulent flame speeds
• Primary heat release
• “Low” temperature chemistry
• Location / Intensity tracking
• Wall quenching
• Lean/rich mixture stratification
Objective: Develop an accurate, robust, versatile G-equation combustion model for PFI/DI SI engine simulations by incorporating detailed chemistry.
Platform: KIVA3V-G Code + Detailed Chemistry Solver.
General ApproachGeneral Approach
Turbulent Flame Propagation
Post-flame Chemistry
Knocking Combustion
Flame Quenching
G-equation ModelG-equation Model
0( ) | | | |uf ve r te x T t
Gv v G S G D G
t
22 2 2 2( ) ( ) 2 ( )u
f vertex t t s
Gv v G D G D G c G
t k
1/ 21/ 2 22 224 3 4 3
4 30 4 1 1
1 1 exp2 2
ignT
L m F F l F
t t a b a bS l l u la b
S I C b l b l S l
Premixed Flame Partially Premixed Flame
CO2, H2O,NO…
End-gas Flame Post-flameZone Front Zone
AutoIgnition
n
G > 0G < 0
G(x,t) = 0
Φ ≈ const
Φ ≈ 1
Φ > 1
Φ < 1
CO2, H2O, CO, NO…
O2, O, NO …
Fuel Droplets
Diffusion
Diffusion
End-gas Flame Post-flameZone Front Zone
CH4, CO, H, H2 …
Transport equations of Favre means of scalar G
and its variance
Turbulent flame speedconsidering kernel
flame evolution
Typical flame structuresobserved in SI engines.
The flame front is numerically tracked by G(x,t)=0 iso-surface.
Reduced PRF mechanism used in engine simulations(Tanaka et al., Combust. Flame, 133, 2003)
Chemical ProcessesChemical Processes
The low-temperature chemistry in the end-gas and the post-flame chemistry
are modeled using detailed chemical kinetics
The primary heat release and species conversion are based on the assumption that the burnt mixture within the turbulent flame brush tends to local and instantaneous chemical equilibrium.
0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.50.01
0.1
1
10
100
Igni
tion
Del
ay T
ime
(m
s)
1000(K) / T0
100% iC8H18 90% iC8H18 / 10% nC7H16 80% iC8H18 / 20% nC7H16 60% iC8H18 / 40% nC7H16 100% nC7H16
Vb
Vu
Mean Flame Front
Burnt
Unburnt
Calculated ignition delay time of PRF fuel
Mercury Marine two-stroke gasoline DI engine
Modeling a Two-Stroke GDI EngineModeling a Two-Stroke GDI Engine
In-cylinder species distributions at CA = 755 ATDC
Flame propagation and temperature contours.Start of injection = 635 ATDC
Spark timing = 679 ATDC
Fuel O2 OH CO NO
Ford DISI engine
Modeling a Ford DISI EngineModeling a Ford DISI Engine
Injection Ignition Flame propagation
Pressure and heat release rateEnd of injection = -72 ATDC
Spark timing = -20, -24, -28, -32 ATDC
-80-60 -40-20 0 20 40 60 80-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0
5
10
15
20
25
Pre
ssur
e (M
Pa)
CA (OATDC)
EXPT SIMU
Hea
t Rel
ease
Rat
e (J
/Deg
)-20 O ATDC
-80-60 -40 -20 0 20 40 60 80-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0
5
10
15
20
25
Pre
ssur
e (M
Pa)
CA (OATDC)
EXPT SIMU
-24 O ATDC
Hea
t Rel
ease
Rat
e (J
/Deg
)
-80 -60 -40 -20 0 20 40 60 80-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0
5
10
15
20
25
-28 O ATDC
Pre
ssur
e (M
Pa)
CA (OATDC)
EXPT SIMU
Hea
t Rel
ease
Rat
e (J
/Deg
)
-80 -60 -40 -20 0 20 40 60 80-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0
5
10
15
20
25
Pre
ssur
e (M
Pa)
CA (OATDC)
EXPT SIMU
-32 O ATDC
Hea
t Rel
ease
Rat
e (J
/Deg
) Knock onset due to end-gas auto-ignition(The dark interface is the deflagrating flame front)
Knocking Combustion ModelingKnocking Combustion Modeling
In-cylinder pressure fluctuation
-60 -50 -40 -30 -20 -10 0 10 200
2
4
6
8
10
12
Pre
ssu
re (
MP
a)
CA (ATDC)
Average Position1 Position2 Position3
Boosted stoichiometric combustion ( manifold pressure = 150 kPa )
1
2
3
Numerical transducers
PFI/DI-SI Engine
•CO Oxidation, H2-O2 reactions
•Pollutant formation
•G-equation description of combustion
•Laminar and turbulent flame speeds
•Primary heat release
•“Low” temperature chemistry
•Location / Intensity tracking
•Wall quenching
•Lean/rich mixture stratification
Objective: Develop an accurate, robust, versatile G-equation combustion model for PFI/DI SI engine simulations by incorporating detailedchemistry.
Platform: KIVA3V-G Code + Detailed Chemistry Solver.
General ApproachGeneral Approach
Turbulent Flame Propagation
Post-flame Chemistry
Knocking Combustion
Flame Quenching
G-equation ModelG-equation Model
0( ) | | | |uf vertex T t
Gv v G S G D G
t
22 2 2 2( ) ( ) 2 ( )u
f vertex t t s
Gv v G D G D G c G
t k
1/ 21/ 2 22 224 3 4 3
4 30 4 1 1
1 1 exp2 2
ignT
L m F F l F
t t a b a bS l l u la b
S I C b l b l S l
Premixed Flame Partially Premixed Flame
CO2, H2O,NO…
End-gas Flame Post-flameZone Front Zone
AutoIgnition
n
G > 0G < 0
G(x,t) = 0
Φ≈const
Φ≈1
Φ> 1
Φ< 1
CO2, H2O, CO, NO…
O2, O, NO …
Fuel Droplets
Diffusion
Diffusion
End-gas Flame Post-flameZone Front Zone
CH4, CO, H, H2…
Transport equations of Favre means of scalar G
and its variance
Turbulent flame speedconsidering kernel
flame evolution
Typical flame structuresobserved in SI engines.
The flame front is numerically tracked by G(x,t)=0 iso-surface.
Reduced PRF mechanism used in engine simulations(Tanaka et al., Combust. Flame, 133, 2003)
Chemical ProcessesChemical Processes
The low-temperature chemistry in the end-gas and the post-flame chemistry
are modeled using detailed chemical kinetics
The primary heat release and species conversion are based on the assumption that the burnt mixture within the turbulent flame brush tends to local and instantaneous chemical equilibrium.
0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.50.01
0.1
1
10
100
Igni
tion
Del
ay T
ime
(ms)
1000(K) / T0
100% iC8H18 90% iC8H18 / 10% nC7H16 80% iC8H18 / 20% nC7H16 60% iC8H18 / 40% nC7H16 100% nC7H16
Vb
Vu
Mean Flame Front
Burnt
Unburnt
Calculated ignition delay time of PRF fuel
Mercury Marine two-stroke gasoline DI engine
Modeling a Two-Stroke GDI EngineModeling a Two-Stroke GDI Engine
In-cylinder species distributions at CA = 755 ATDC
Flame propagation and temperature contours.Start of injection = 635 ATDC
Spark timing = 679 ATDC
Fuel O2 OH CO NO
Ford DISI engine
Modeling a Ford DISI EngineModeling a Ford DISI Engine
Injection Ignition Flame propagation
Pressure and heat release rateEnd of injection = -72 ATDC
Spark timing = -20, -24, -28, -32 ATDC
-80 -60 -40 -20 0 20 40 60 80-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0
5
10
15
20
25
Pre
ssur
e (M
Pa)
CA (OATDC)
EXPT SIMU
Hea
t Rel
ease
Rat
e (J
/Deg
)-20 O ATDC
-80 -60 -40 -20 0 20 40 60 80-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0
5
10
15
20
25
Pre
ssur
e (M
Pa)
CA (OATDC)
EXPT SIMU
-24 O ATDC
Hea
t Rel
ease
Rat
e (J
/Deg
)
-80 -60 -40 -20 0 20 40 60 80-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0
5
10
15
20
25
-28 O ATDC
Pre
ssur
e (M
Pa)
CA (OATDC)
EXPT SIMU
Hea
t Rel
ease
Rat
e (J
/Deg
)
-80 -60 -40 -20 0 20 40 60 80-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0
5
10
15
20
25
Pre
ssur
e (M
Pa)
CA (OATDC)
EXPT SIMU
-32 O ATDC
Hea
t Rel
ease
Rat
e (J
/Deg
)
Knock onset due to end-gas auto-ignition(The dark interface is the deflagrating flame front)
Knocking Combustion ModelingKnocking Combustion Modeling
In-cylinder pressure fluctuation
-60 -50 -40 -30 -20 -10 0 10 200
2
4
6
8
10
12
Pre
ssur
e (M
Pa)
CA (ATDC)
Average Position1 Position2 Position3
Boosted stoichiometric combustion ( manifold pressure = 150 kPa )
1
2
3
Numerical transducers