Efficient Engine CFD with Detailed Chemistry

Transcription

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

2 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

3 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

4 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

5 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

6 DARS-CFD STAR-CD coupling STAR-CD: Species Y i 0 Enthalpy h Species Y i * Transport data D ij,, DARS-CFD Efficient Engine CFD with Detailed Chemistry 6

7 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

8 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

9 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

10 Basics of the flamelet model Physical Coordinates Mixture fraction coordinate Z i tx,, x, x, ZZ,, Z Flame: Surface of Stoichiometric mixture Efficient Engine CFD with Detailed Chemistry 10

11 Basics of the flamelet model Transport of a generic scalar Flamelet transform: Def. Scalar dissipation rate Equations in flamelet space Efficient Engine CFD with Detailed Chemistry 11

12 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 Efficient Engine CFD with Detailed Chemistry 12

13 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) K Netzell, H Lehtiniemi, and F Mauss, Proc Combust Inst 31 (2007) Efficient Engine CFD with Detailed Chemistry 13

14 Soot modeling with TIF Centerline soot volume fracition ] : [ f v Height [mm] F Mauss, K Netzell, and H Lehtiniemi, Combust Sci and Tech 178 (10-11) (2006) K Netzell, H Lehtiniemi, and F Mauss, Proc Combust Inst 31 (2007) Efficient Engine CFD with Detailed Chemistry 14

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

16 Transient flamelet progress variable model Progress variable defined using chemical enthalpy integrated over the flamelet 1 N 1 s Ns h ( ( ) ) ( ( ) 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 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) Efficient Engine CFD with Detailed Chemistry 16

17 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) Efficient Engine CFD with Detailed Chemistry 17

18 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 mm 1176 rpm Diesel mg CA 0.32 H Lehtiniemi, F Mauss, M Balthasar and I Magnusson, SAE Efficient Engine CFD with Detailed Chemistry 18

19 TFPV Sample engine calculation : [ s s e r g o r P Combustion progress Max progress Mean progress Crank angle [deg] P [ Pressure and rate of heat release e r u s s e r P Crank angle [deg] H Lehtiniemi, F Mauss, M Balthasar and I Magnusson, SAE R a t e o f h e a t r e l Efficient Engine CFD with Detailed Chemistry 19

20 TFPV Sample engine calculation CA 380 Temperature Mixture fraction T [K] Z [-] H Lehtiniemi, F Mauss, M Balthasar and I Magnusson, SAE Efficient Engine CFD with Detailed Chemistry 20

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

22 TFPV Sample engine calculation, CA 395 Temperature Mixture fraction T [K] Z [-] H Lehtiniemi, F Mauss, M Balthasar and I Magnusson, SAE Efficient Engine CFD with Detailed Chemistry 22

23 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 Efficient Engine CFD with Detailed Chemistry 23

24 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 Efficient Engine CFD with Detailed Chemistry 24