CFD Combustion Models for IC Engines Rolf D. Reitz · Auto-ignition and Detailed Chemistry Models...
Transcript of CFD Combustion Models for IC Engines Rolf D. Reitz · Auto-ignition and Detailed Chemistry Models...
CFD Combustion Models for IC Engines
Rolf D. Reitz
Engine Research Center
University of Wisconsin-Madison
http://www.cae.wisc.edu/~reitz
ERC Symposium, June 7, 2007
1. Characteristic Time Combustion Model (KIVA-CTC)
• Auto-ignition model (SHELL) – ignition with 8 reaction steps
• Combustion model (CTC) – turbulence mixing timescales
2. Representative Interactive Flamelet Model (KIVA-RIF)
• Flamelet equations/detailed chemistry coupled with CFD (Peters et al.)
• Effect of turbulence is modeled with average scalar dissipation rate
3. Direct Integration of CFD with Chemistry (KIVA-CHEMKIN)
• Each computational cell treated as well stirred reactor
• ERC reduced mechanism for n-heptane – chemistry timescales
4. KIVA-CHEMKIN-G Model
• Explicit modeling of turbulent flame propagation combined with detailed
chemistry
Turbulence vs. chemistry time scalesTurbulence vs. chemistry time scales
Combustion and Emission Models at the ERC
Eddy breakup
timescales
Chemistry
timescales
Auto-ignition and Detailed Chemistry Models
Gasoline
Diesel
Bio-diesel
Aromatic
EhthanolAlcohol
25 species
51 reactions
30 species
65 reactions
41 species
150 reactions
Comprehensive
mechanism
Skeletal
mechanism
Multi-fuel
Mechanism
(ERC-PRF-Bio)
Skeletal Chemistry Mechanism for Multi-Surrogate Fuels
Multi-component fuelsurrogate fuel
857 species
3586 reactions
570 species
2580 reactions
264 species
1219 reactions
Iso-octane
N-heptane
Methyl
butanoate
Toluene
Dr. Youngchul Ra
Jessica Brakora
SAE 2004-01-0558,
SAE 2007-01-0190,
SAE 2007-01-0165
47
41
Shock tube measurements
(Fieweger et al. 1997)
Calculation using ERC-PRF
mechanism
Validation - Auto-ignition Model
n-heptane-iso-octane/air mixtures, stoichiometric, P=40 Bar)
SAE 2007-01-01650.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5
0.01
0.1
1
10
100
Ignitio
n D
ela
y T
ime (
ms)
1000(K)/T
100% i-octane 90% i-octane / 10% n-heptane 80% i-octane / 20% n-heptane 60% i-octane / 40% n-heptane 100% n-heptane
Validation – Cat HD engine
0
20
40
60
80
100
120
140
160
180
0.135 0.20 0.23 0.27 0.29 0.39
CO
(g
/Kg
f)
Equivalence ratio
Experiment Shell-CTC Chemkin
-40 -20 0 20 40
0
1
2
3
4
5
6
0
100
200
300
400
500
600
700
800
900 Experiment Shell-CTC CHEMKIN
P
ressure
(M
Pa)
CAD ATDC
AH
RR
(J/d
eg)
rpm = 1737eq_ratio = 0.23 c_ratio = 16.1inj_timing = -113 ca
-40 -20 0 20 40
0
1
2
3
4
5
6
0
100
200
300
400
500
600
700
800
900700 rpmeq_ratio = 0.27c_ratio = 16.1inj_timing = - 274.5 ca
Pre
ssure
(M
Pa)
CAD ATDC
Experiment Shell-CTC CHEMKIN
AH
RR
(J/d
eg)
SAE 2002-01-0418, SAE 2007-01-0190
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0.135 0.20 0.23 0.27 0.29 0.39
NO
x (
g/K
gf)
Equivalence ratio
Experiment Shell-CTC Chemkin
Gasoline HCCI
Validation - GM Light-duty Diesel Engine
GM 1.9L 4-cylinder
Bore Stroke 82 90.4 mm
Compression Ratio 16.6: 1
Engine Speed 2000 rev/min
IMEP 5.5 Bar
EGR 67% PCCI
SAE 2007-01-0193
SOIC = –39, -32 and –23
SOIC=-32
KIVA-CHEMKIN
Advances in SI Engine Combustion Modeling
G-equation Combustion Model with Detailed Chemical Kinetics
SAE 2007-01-0165
GkDGSGvvt
GTT
uvertexf
~~~~)(
~0
=+
End Gas
G-Equation
Flame
propagationBurnt Gas
Discrete particle
ignition model
SAE 2000-01-2809
SAE 2003-01-0722
Auto-ignition
(detailed
kinetics)
-100 -50 0 50 1000.0
0.5
1.0
1.5
2.0
2.5
PFI mode
-32 OATDC
Pre
ssu
re (
MP
a)
Crank Angle (oATDC)
EXPT SIMU
-100 -50 0 50 1000.0
0.5
1.0
1.5
2.0
2.5
Pre
ssu
re (
MP
a)
Crank Angle (oATDC)
EXPT SIMU
PFI mode
-44 OATDC
PFI Spark
sweep
Ford DISI
Bore Stroke 89 79.5 mm
Compression Ratio 12 : 1
Engine Speed 1500 rev/min
DI Spark
sweep
-80 -60 -40 -20 0 20 40 60 80 100-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0
5
10
15
20
25
Pre
ssu
re (
MP
a)
Crank Angle (oATDC)
EXPT SIMU
Heat
Rele
ase R
ate
(J/D
eg
Spk = -20 oATDC
-80 -60 -40 -20 0 20 40 60 80 100-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0
5
10
15
20
25
Pre
ssu
re (
MP
a)
Crank Angle (oATDC)
EXPT SIMU
Spk = -32 oATDC
Heat
Rele
ase R
ate
(J/D
eg
-80 -60 -40 -20 0 20 40 60 80 100-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0
5
10
15
20
25
30
35
Pre
ssu
re (
MP
a)
Crank Angle (oATDC)
EXPT SIMU
Heat
Rele
ase R
ate
(J/D
eg
MAP = 75 kPa
-80 -60 -40 -20 0 20 40 60 80 100-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0
5
10
15
20
25
30
35
Pre
ssu
re (
MP
a)
Crank Angle (oATDC)
EXPT SIMU
Heat
Rele
ase R
ate
(J/D
e
MAP = 100 kPa
DI MAP
sweep
SAE 2007-01-0165
Validation – Ford SI EngineKIVA-CHEMKIN-G
-15 -10 -5 0 5 10 15 20 25
0
200
400
600
800
1000
1200
Injection Profile
Pre
ssu
re (
MP
a)
AH
RR
(J
/de
g)
CAD ATDC
-1
0
1
2
3
4
5
6
7
8
9High-T, Long-ID TEST
CHEMKIN G_Model
O2 = 21%
SOI = -5
Experiment KIVA-CHEMKIN KIVA-CHEMKIN-G
Validation - Sandia Cummins Diesel
High-T, long-ID Condition (Premixed Combustion)
SAE 2006-01-0055
Green: OH
Red: Soot
Experimental
-20 -15 -10 -5 0 5 10 15 20 25 30 35 40
0
300
600
900
1200
1500
1800 Case 1 Case 2 Case 3 Case 4 Case 5
Experimental Measurements
AH
RR
(J
/de
g)
CAD ATDC
-2
0
2
4
6
8
10
12
14
16
Pre
ssu
re (
MP
a)
KIVA-CHEMKIN-G
-20 -15 -10 -5 0 5 10 15 20 25 30 35 40
0
300
600
900
1200
1500
1800 Case 1 Case 2 Case 3 Case 4 Case 5
Model Predictions
AH
RR
(J
/de
g)
CAD ATDC
-2
0
2
4
6
8
10
12
14
16
Pre
ssu
re (
MP
a)
Validation - Cummins Dual-Fuel Engine
Case1 Case2 Case3 Case4 Case50.000
0.005
0.010
0.015
0.020
0.025
0.030
NOx
Em
iss
ion
s (
gra
ms
)
C
Measured
Predicted
NOx
SAE 2007-01-0171
Case 1 2 3 4 5
TIVC (K) 392 397.5 403 405 408
BMEP 10 bar
SOI -87 BTDC
PIVC 2.1 bar
NG 0.44
CR 14.5
Primary Fuel:
Natural Gas
Ignition Source:
Diesel Pilot (10%)
KIVA-CHEMKIN vs KIVA-CHEMKIN-G
-50 -40 -30 -20 -10 0 10 20 30 40 50
0
300
600
900
1200
1500
1800 Test KIVA-CHEMKIN
AH
RR
(J/d
eg
)
CAD ATDC
-2
0
2
4
6
8
10
12
14
16Case 1
Pre
ssu
re (
MP
a)
-50 -40 -30 -20 -10 0 10 20 30 40 50
0
300
600
900
1200
1500
1800 Test KIVA-CHEMKIN-G
AH
RR
(J/d
eg
)
CAD ATDC
-2
0
2
4
6
8
10
12
14
16Case 1
Pre
ssu
re (
MP
a)
Without flame-
propagation
combustion is
too slow
Validation - Cummins Dual-Fuel Engine
Summary and Conclusions
• Current CFD models describe important physical and chemical
processes of engine flows, but validation experiments are needed
for model development and improvement
• CFD combustion models capture engine performance and
emissions trends and can be combined with optimization tools for
design and evaluation of engine design concepts
• Methodologies are in place for modeling a wide range of
combustion regimes:
HCCI PCCI Diesel SI flame propagation dual-fuel
• Multi-component fuel vaporization models can be coupled with
advanced chemical kinetics models
• Surrogate fuel models are under development to represent
representative practical fuels (MB, toluene, ethanol…..)
Multi-Component fuel modeling – Dr. Youngchul Ra
Diesel
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0
10
20
30
40
50
0 50 100 150 200 250 300
gasoline composition
iso-octane approximation
distribution or mole
distribution or mol
molecular weight
Continuous fp(I)
Discrete gp(mwi)
Single comp approx
6.393-C/H ratio
0.3%Olefins
42%Napthenes
42%Paraffins
7.3ppmSulfur
16%Aromatics
Gasoline* * Adapted from J. Farrel, Exxon Mobil Corp.
PRF50: Emissions
0.00
0.05
0.10
0.15
0.20
0.25
-50 -45 -40 -35 -30 -25 -20
start of injection command [deg ATDC]
NO
x [
g/k
g-f
]
PRF50
Diesel-sgl
NOxLTC regime (EGR=65%)
Injection sweep
0
20
40
60
80
100
120
140
-50 -45 -40 -35 -30 -25 -20
start of injection command [deg ATDC]
HC
at
EV
O [
g.k
g-f
]
PRF50
Diesel-sgl
HC0
100
200
300
400
500
600
700
800
-50 -45 -40 -35 -30 -25 -20
start of injection command [deg ATDC]
CO
at
EV
O [
g/k
g-f
]
PRF50
Diesel-sgl
CO
Reduced Biodiesel Mechanism – Jessica Brakora
Mechanism Reduction Method– SENKIN constant volume analysis
– Identify key species and reaction pathsbased on ignition timing
• Peak concentration: remove species thatnever exceed specified mole fractionthresholds (-112 species)
• XSENKPLOT reaction flux analysis:identify key reaction pathways, removeless important paths (-111 species)
– Adjust rate constants for key reactionsto optimize ignition timing
XSENKPLOT reaction paths: MB fuel breakup
Large flux to “mb2j” (C5H9O2);test removal of other paths
LLNL methyl butanoate (MB)*
– Surrogate to represent the large methylesters in biodiesel
– MB chemical formula: C5H10O2
– 264 species, 1219 reactions
*Proc. Comb. Inst., Vol 28, 2000/pp.1579-1586
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
600 700 800 900 1000 1100 1200 1300 1400
Initial Temperature [K]
Ign
itio
n D
ela
y [
s]
LLNL detailed (264 species)
rm spec < 10 -̂10 (199 spec)
rm spec < 10 -̂9 (179 spec)
rm spec < 10 -̂8 (162 spec)
No noticeable change in ignition;these species can be removed
Reduced MB Kinetic Mechanism
P = 40bar, Phi = 1.0
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
600 700 800 900 1000 1100 1200 1300 1400
Initial Temperature [K]
Ign
itio
n D
ela
y [
ms
]
LLNL detailed
MB reduced
mb
mb2ooh mb2oo mb2j
ch3o2h (ch3o, ch2o, ch3o2)
mb2o
c2h5chome2*o
me2j*o
(ch2co,ch3oco)
(ch3oco) mp2d
ch2cho
ch2co(c2h5)
(ch2o)
mb2ooh4j
mb2ooh4oo
mb4ooh2*o
mp3j2*o
(ch3oco, ch2co)
These species further break down into
lower-level carbon species
MB reduced coupled with ERC n-heptane: 41 species, 150 reactions
ERC n-heptane mechanism SAE 2004-01-0558: 34 species
ERC PRF Reduced Chemistry SAE 2007-01-0190, SAE 2007-01-0165: 47 species
Auto-ignition and Detailed Chemistry Models
OH
RH + O2 ROOH
ORO
First Stage Ignition
Olefin
RH + O2
HO2 H2O2
H2O2 + (M) OH + OH +
(M)
Second Stage Ignition
Diesel Gasoline
Multi-component Fuel – DMC/PRF Models
0
2
4
6
8
10
12
14
-30 -20 -10 0 10 20 30 40 50
CA [deg ATDC]
pre
ss
ure
[M
Pa
]
0
40
80
120
160
200
240
280
HR
R [
J/d
eg
]
P, inj= -45
P, inj= -42
P, inj= -39
P, inj= -33
P, inj= -27
P, inj= -21
P, iC8
P, nC7
HRR, inj= -45
HRR, inj= -42
HRR, inj= -39
HRR, inj= -33
HRR, inj= -27
HRR, inj= -21
HRR, iC8
HRR, nC7
iso-octane
n-heptane
PRF50 fuel