Efficient Engine CFD with Detailed Chemistry

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Efficient Engine CFD
with Detailed Chemistry
Harry Lehtiniemi and Rajesh Rawat
CD-adapco
Karin Fröjd and Fabian Mauss
Digital Analysis of Reaction Systems

Challenges in CFD engine modeling
• The flow is turbulent
– Turbulence modeling required
• Spray injection and evaporation occurs
– Spray modeling is required
• Autoignition, combustion, pollutant formation chemistry
– Kinetic modeling required for various fuels
– Soot, NOx models required
Efficient Engine CFD with Detailed Chemistry 2

Efficient Engine CFD with Detailed Chemistry
Problem: Multidimensional modeling of turbulent reactive flow
Turbulent flowfield
Combustion
Navier-Stokes equations ?
Efficient Engine CFD with Detailed Chemistry 3

Outline
• Species transport models
– ”Laminar”
– Techniques for speed-up
– Incorporation of turbulence interactions
• Flamelet models
– Transient interactive flamelets
– Transient flamelet progress variable model
Requirements for industrial production simulations:
Efficient handling of combustion chemistry
Fully parallel flow simulation capabilities
Efficient Engine CFD with Detailed Chemistry 4

STAR-CD and DARS-CFD
Problem: Multidimensional modeling of turbulent reactive flow
Solution I:
Turbulent flowfield
Combustion
Navier-Stokes equations
Species transport
Efficient Engine CFD with Detailed Chemistry 5

DARS-CFD – STAR-CD coupling
STAR-CD:
Species Y i
0
Enthalpy h
Species Y i
*
Transport data D ij , ,
DARS-CFD
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DARS-CFD – STAR-CD coupling with DOLFA
STAR-CD:
DOLFA
Database
Species Y i
0
Enthalpy h
DOLFA
Species Y i
*
Transport data D ij , ,
DARS-CFD
Efficient Engine CFD with Detailed Chemistry 7

DARS-CFD – STAR-CD with turbulence interactions
Two options for considering turbulence interactions:
• Kong-Reitz model:
• User coding:
– Scaling of reaction rates
– User can modify the reaction rates for all species
Efficient Engine CFD with Detailed Chemistry 8

STAR-CD and Transient Flamelet Models
Problem: Multidimensional modeling of turbulent reactive flow
Solution II:
Turbulent flowfield
Combustion
Navier-Stokes equations
Flamelet modeling
- Interactive
- Transient library
Efficient Engine CFD with Detailed Chemistry 9

Basics of the flamelet model
Physical Coordinates Mixture fraction coordinate Z i
tx , , x, x
, ZZ , , Z
1 2 3 2 3
Flame: Surface of
Stoichiometric mixture
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Basics of the flamelet model
Transport of a generic scalar
Flamelet transform:
Def. Scalar dissipation rate
Equations in flamelet space
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STAR-CD – TIF coupling
STAR-CD
Transport of Z, Z” 2 , h, I
Z, Z” 2 T, W q
Update h and
Get cell local T and W q
Perform species pdf integration
Y i (Z)
TIF
2
Yi
Yi
= +
2 iWi
t
2 Z
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Soot modeling with TIF
• Turbulent diffusion flame (J. B. Moss et al. 1991) test case
• Flowfield post-processed with TIF
• Detailed kinetic soot model
– Soot precursors: cyclopentapyrene and larger PAH
– Surface growth: HACA with separate ring closure
– Oxidation: O 2 and OH
– Condensation and coagulation
• Particle size distribution
– Method of moments with interpolative closure (4 moments)
– Sectional method (100 sections)
F Mauss, K Netzell, and H Lehtiniemi, Combust Sci and Tech 178 (10-11) (2006) 1871-1885
K Netzell, H Lehtiniemi, and F Mauss, Proc Combust Inst 31 (2007) 667-674
Efficient Engine CFD with Detailed Chemistry 13

Soot modeling with TIF
Centerline soot volume fracition
]
:
[
f v
2 10 -6
1.5 10 -6
1 10 -6
2.5 10 -6
5 10 -7
0 100 200 300 400
0
Height [mm]
F Mauss, K Netzell, and H Lehtiniemi, Combust Sci and Tech 178 (10-11) (2006) 1871-1885
K Netzell, H Lehtiniemi, and F Mauss, Proc Combust Inst 31 (2007) 667-674
Efficient Engine CFD with Detailed Chemistry 14

Soot modeling with TIF
Particle size distributions in the turbulent diffusion flame
K Netzell, H Lehtiniemi, and F Mauss, Proc Combust Inst 31 (2007) 667-674
Efficient Engine CFD with Detailed Chemistry 15

Transient flamelet progress variable model
• Progress variable defined using chemical enthalpy integrated over the
flamelet 1 N
1
s
Ns
h
0 1 298
( ( ) )
0 1 298
( ( ) 0)
i , i
Yi Z , dZ h
i u
Yi
Z dZ
= i
, ,
,
=
C =
,
1 N
1
s
Ns
h ( Y( Z) , ) dZ h ( Y( Z) , 0) dZ
h h h
0 i= 1 298,, ib i
0 i=
1 298,,
iu i
Transport eqn for chemical enthalpy
2
298 298 298
+ v
D =
2
ihi
, 298
t x x
i=
1
N s
Transport eqn for the progress variable
h
+ v D = C
t x x h /C t
2
C C C
2
Transform to Z – C space
Z
C
= + +
t Z t C t t
Z
C
= +
x Z x C x
H Lehtiniemi, F Mauss, M Balthasar and I Magnusson, Combust Sci and Tech 178 (10-11) 2006 1977-1997
298
298
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TFPV – Coupling to STAR-CD
CFD
To library
EGR, p( t), Tox( x, t),
( x, t), C
( x, t)
Flamelet library module
IdentifyFlamelet
EGR, p( t), T ( x, t), ( x, t), C
( x, t)
ox
C
( x, t)
hflamelet
( T
, Z)
Transport of
Z
t Z
t
2
( x, ), ( x, )
1
2
hi( T ) YiP ( Z; Z , Z ) dZ
0
2
CZZ , , , h
h
flamelet
( T
)
T
( x, t) , h
( x, t)
guess
IterateTemperature
T( x, t) = f ( T ( x, t), h( x, t), h
( T))
guess
flamelet
To CFD
T
( x, t)
T
( x, t)
C
( x, t)
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TFPV – Sample engine calculation
Swept volume
Compression ratio
Number of nozzle holes
Nozzle hole diameter
Speed
Fuel type
Fuel amount
Start of injection
EGR ratio
2.0 L
15.3
6
0.2 mm
1176 rpm
Diesel
74.35 mg
1.24
361 CA
0.32
H Lehtiniemi, F Mauss, M Balthasar and I Magnusson, SAE 2005-01-3855
Efficient Engine CFD with Detailed Chemistry 18

TFPV – Sample engine calculation
:
[
s
s
e
r
g
o
r
P
1
0.8
0.6
0.4
0.2
Combustion progress
___
Max progress
___
Mean progress
0
350 360 370 380 390 400 410
Crank angle [deg]
Pressure and rate of heat release
P
[ 4 10 6 700
3.5 10 6
e
600
r 3 10 6
500
u
s2.5 10 6
400
s
2 10 6
e
300
r1.5 10 6
P
1 10 6
200
5 10 5
100
0
0
350 360 370 380 390 400 410
Crank angle [deg]
H Lehtiniemi, F Mauss, M Balthasar and I Magnusson, SAE 2005-01-3855
R
a
t
e
o
f
h
e
a
t
r
e
l
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TFPV – Sample engine calculation CA 380
Temperature Mixture fraction T [K] Z [-]
2300
0.4
300
0
H Lehtiniemi, F Mauss, M Balthasar and I Magnusson, SAE 2005-01-3855
Efficient Engine CFD with Detailed Chemistry 20

TFPV – Sample engine calculation, CA 385
Temperature Mixture fraction T [K] Z [-]
2300
0.4
300
0
H Lehtiniemi, F Mauss, M Balthasar and I Magnusson, SAE 2005-01-3855
Efficient Engine CFD with Detailed Chemistry 21

TFPV – Sample engine calculation, CA 395
Temperature Mixture fraction T [K] Z [-]
2300
0.4
300
0
H Lehtiniemi, F Mauss, M Balthasar and I Magnusson, SAE 2005-01-3855
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Summary
• Strategies for efficiently incorporating detailed chemistry in
multidimensional simulations were presented:
– Direct integration of chemistry with DARS-CFD
– Flamelet approach
» Transient interactive flamelet (TIF)
» Transient flamelet progress variable model (TFPV)
• The DARS-CFD model allows for
– Turbulence interactions (Kong-Reitz) or user
– Coupling to DOLFA
– Full parallelism
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Summary
• The TIF model allows for
– Efficient treatment of chemistry
– Consistent handling of turbulence interactions
– Efficient treatment of complex soot and emission chemistry
– Fully parallel simulations
• The TFPV model allows for
– Consideration of effects of local inhomogeneities and local
variations of scalar dissipation rate on the chemistry
– Arbitrary large chemistry can be used in the tabulation without
influencing the CFD simulation CPU time
– Coupling to library based emission models
– Fully parallel simulations
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