Modelling of Gasoline Combustion using ECFM-3Z With STAR-CD V4 Investigation on spark modelling with AKTIM and Knock. Your subtitle goes here

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1 Modelling of Gasoline Combustion using ECFM-3Z With STAR-CD V4 Investigation on spark modelling with AKTIM and Knock Your subtitle goes here

2 TOPICS SI modelling with ECFM-3Z Fundamental and Numerics KNOCK models AKTIM : Spark model Applications AKTIM and Knock with T.K.I-P.DF illustrate the above with examples Conclusions 2

= f(p,t u,y ui,..) N2 CO CO N2 NO H2O H2O N NO d L = f(p,t u,t b,.

3 ECFM-3Z : Conceptual Framework MIXING MODEL Auto-Ignition FUEL UNBURNED GASES BURNED GASES CnHm H2 CnHm H2 O O2 O2 CO2 CO2 U L = f(p,t u,y ui,..) N2 CO CO N2 NO H2O H2O N NO d L = f(p,t u,t b,..) H OH AIR + EGR U L T u, Y u T b, Y b S A Hierarchical Approach 3

The Extended Coherent Flame Model-3Z MAJOR

H 2 2 OH O 2 + 2H 2 O 4 OH O 2 +2CO 2 CO 2 Kinetic

CO 2 + H Soot Auto-ignition Delay Wisconsin Model

Reactions are solved using conditioned burnt gases

4 The Extended Coherent Flame Model-3Z MAJOR HYPOTHESIS Equilibrium N 2 2 N O 2 2 O H 2 2 H O 2 + H 2 2 OH O 2 + 2H 2 O 4 OH O 2 +2CO 2 CO 2 Kinetic O2 + N2 N + NO O2 + N O + NO N + OH H + NO CO + OH CO 2 + H Soot Auto-ignition Delay Wisconsin Model Based on experimental Correlation or tables Reactions are solved using conditioned burnt gases properties (un-burnt gases for Auto-ignition and laminar flame properties) 4

5 ECFM-3Z MODEL: FLAME AREA DENSITY EQUATION Generation due to interaction with turbulence Flame wall interaction Intermittent stretch function due to strain and curvature ITNFS function (Intermittent Turbulence Net Flame Stretch) Consumption to flame propagation Change due to gas compression/expansion Change due to flame expansion Initiation due to ignition (spark or knock 5

6 Flame Surface Density Transport Equation : 3Z Generation due to interaction with turbulence t t K K k, S, d,, l ITNFS function l l t v, /S L Wellstirred reactor Da<1 Ret= 1 Engine combust ion Da=1 Distributed reaction zones Da>1,Ka>1 Ka<1 Corrugated flamelets Wrinkled flamelets Misfire limit Ka=1 k : turbulent kinetic energy Sl : Laminar flame speed δl: Laminar flame thickness lt : Integral turbulent length scale l t /l F 6

7 THE TURBULENT BURNING VELOCITY The K.P.P (Kolmogorov, Petrovski, Piskunov) asymptotic theory One dimensional turbulent flame in a frozen turbulent flow Constant density Zero mean strain Analytic solution for turbulent burning is obtained using the KPP theorem For ECFM-3Z flame surface density transport equation : UT Kt * C / Sc 1/ 2 * U ' ITNFS function 7

8 Experimental data from Abdel-Gayed and Bradley Propane mixture : Turbulent burning velocity function of U and equivalence ratio Quenching due Intermittency 8

9 Sub-models linked to ECFM-3Z Spark Ignition FI-ECFM (rough standard model) AKTIM Auto-Ignition (including knock modelling) Correlation TKI-PDF 9

10 NEW PRACTICE IN STAR-CD V4.12!!! Switches : SW8 : off SW 22 : off SW107 ON for time step independent Rhie & Chow formula ONLY When Small type step is used (<0.5e-6) USE MARS SCHEME FOR SCALAR AND TEMPERATURE 10

11 Convected scalar trough a uniform 45 Space discretitstaion effect on solution Scalar and velocity 11

Convected scalar trough a uniform velocity @ 45 UDS Min=0 Max=0.

12 Convected scalar trough a uniform 45 UDS Min=0 Max=0.3 MARS with Limiters Min=0 Max=0.99 First Order Second Order Scalar second! 12

13 Numerical Test case Convected vortex in a 2D periodic box WHY? Because: This test case have EXACT solution. Domain size, convective velocity, Vortex size can be easily adapted to SITUATION U x 10 m/s u R c 2 ye x 2 y 2 2R c 2 y v R c 2 xe x 2 y 2 2R c 2 Periodicity x Periodicity x 2 y 2 p p R e R c c 2D structured mesh 80 x 80 13

COMPARE TO ANLATYCAL SOLUTION ALL runs using MARS Plots show pressure

14 Numerical Test case Convected vortex in a 2D periodic box dt=5e-3s dt=1e-3s dt=1e-4s dt=1e-5s Analytical solution Results after 5 turns around time AND COMPARE TO ANLATYCAL SOLUTION ALL runs using MARS Plots show pressure contours Solution Converges from dt=1e-5s Compare VERY WELL to the analytical solution 14

15 Verify combustion model under simplistic conditions HAMAMOTO TEST CASE Using ECFM-3Z combustion model Objective: Verify combustion model under simplistic conditions: Constant Volume Vessel with an engine-like flow pattern Geometry, Initial and Boundary conditions are defined : HAMOMOTO and al. The effect of Swirl on the Combustion of a Homogeneous Mixture in a Closed Vessel, JSME International Journal, Series II, Vol.31, 1988 We present the test case and results obtained using the ECFM-3Z combustion model 15

16 HAMAOTO schematic diagram of experimental apparartus Closed Vessel 16

Increasing swirl level and turbulence 1.Flame is Thick 2.

17 Hamamoto experiments : Typical Sclieren photographs Ὠ : Swirl Velocity at Spark Timing Equivalence Ratio = 1. Increasing swirl level and turbulence 1.Flame is Thick 2.From : Wrinkled flamelets to distributed reaction zones 17

18 Mesh and : Boundary Walls Symetry plane Spark location Cyclics 18

19 Models ECFM-3Z combustion model Turbulence model : k EPS RNG High Reynolds Wall heat transfer : Modified ANGELBERGER Ignition model : Standard Ignition model for ECFM-3Z : 2.5mm initial flame kernel distributed around the ignition point following a Gaussian distribution which width is of the order of the integral turbulent length scale Laminar flame speed : METGHALGI and KECK correlation for Propane All model parameters are default Solver setting for ECFM-3Z combustion Time-step = 1 micro second 19

20 Flow : Initial conditions : From measurements Velocity profile : U2 Turbulent Intensity profile : TI 20

21 Results (I) : Mean Chamber Pressure and Heat Release Rate over time Pressure Heat Release * *Using the method of Lavoie 21

22 Results (II) : Flame front position in XZ-plane Experiments : 8.0ms 12ms Time of arrival at ion probe installed at various location 4.2ms 6.4ms 10.0ms Predicted: Maximum Rate of reaction 4.2ms 6.4ms 8.0ms 10.0ms 12ms 22

23 Results (II) : Flame front profiles in XZ-plane 4.2, 6.4, 8, 10 and 12 ms after Ignition Solid lines : CFD Dashed lines : Experimental The CFD contours correspond to The maximum of Rate of Reaction (Propagation) 23

24 Knock analysis standard one intermediate specie model 1 ) An intermediate species integrates the advance in the auto ignition process. When the delay is reached, the mixed fuel is oxidized with a chemical characteristic time. 2) Before ignition, the evolution of the intermediate species I is computed as follow in the mixed unburnt area dy I /dt = Y Tfu F( d ), F is a function of the delay time d 3) The knock phenomenon starts when the mass fraction of intermediate exceeds the mass fraction of the fuel tracer (Y I >Y Tfu ) 4) When the delay is reached, the intermediate species concentration is computed as follow : dy I /dt = 0.1 Y I / c / u Y Fu Where c is the chemical characteristic time 5) The fuel mass fraction evolution is : dy Fu /dt = - Y Fu / c 6) The delay time is evaluated as follow : D = a*(octa/100) b *(P/(1+XRES)) c e Ta/Tu with a,b, c and Ta, some constant model s constants. Fuel RON to be specified in the IC setup 24

25 EXAMPLE OF ECFM-3Z GASOLINE CALCULATION : Comparison with experiments The results of the ECFM-3Z combustion model are presented here: With and without knock model With a variation of the octane index With a variation of SI timing with a fixed octane index 25

26 ECFM-3Z Combustion Simulation : FIRST OBSERVATIONS Use of ECFM-3Z model along with standard FIECFM spark ignition model provides good results compared with experiments Variations of octane index and SI timing have been done and can be used to predict knocking limit 26

NEW TRENDS PERFORMANCE / FUEL COMSUMPTION/EMISSION For the customer High Power is a headline selling point High Torque gives good acceleration and feel For the industry Specific power (100 hp/liter

27 NEW TRENDS PERFORMANCE / FUEL COMSUMPTION/EMISSION For the customer High Power is a headline selling point High Torque gives good acceleration and feel For the industry Specific power (100 hp/liter and higher) and torque increasing (12 bars BMEP and higher) Pressure charging more common (mechanical and turbo Charging, VIS, VAC) GDI technology (Spray Guided) Control systems more sophisticated ( Spark Energy Knock ) 27

28 Lagrangian spark ignition model Arc and Kernel Tracking Ignition Model The Aktim model laminar to turbulent transition phase fully turbulent phase spark timing Aktim + CFM model S2 4 lagrangien source ECFM model S b,ign 0 t ign t 2 time S 2 r 2 time t 2 fully turbulent ECFM model spark duration t s 28

Ignition Breakdown phase Spark phase Glow phase Electrical

29 Arc and Kernel Tracking Ignition Model Model description Initialization v ie (t) (Inter-electrode voltage) Breakdown! Ignition Breakdown phase Spark phase Glow phase Electrical Circuit Spark Initialization Spark deformation by the mean flow Flame kernels 29

30 AKTIM : A schematic PRESENTATION Secondary electrical circuit Rs Rs : Resistance secondary circuit Ls Ls : Coil Inductance secondary circuit Es : Energy in the secondary circuit 30 Simplified of coil / Inductive ignition system

31 AKTIM SET-UP AND BEST PRACTICES AKTIM is fully set-up by the following extended data : LAKTIM : Flag to activate AKTIM ignition model MAXSP1 : Maximum number of spark kernels per spark plug 1000 MAXKE1 : Maximum number of flame kernels per spark plug EAKGL0 : Secondary circuit electrical energy [J] 0.06 SINDUC : Secondary circuit inductance [mh] 2780 SRESIS : Secondary circuit resistance [Ohm] 1590 RKERNE : Flame kernel radius from which ignition transits to combustion [m] BAKT : Coefficient in correlation for gas tension calculation VAFALL : Tension drop at anode [Volts] VCFALL : Tension drop at cathode [Volts]

32 AKTIM SET-UP AND BEST PRACTICES HTRANSEL : Heat transfer coefficient between flame kernels and walls 2000 NUMSPK : Number of spark plug considered : Ingition timing [s] : Anode location (x y z) in csys 1 in the model unit [mm] followed by maximum distance from anode-cathode axis, at which flame kernels are deposited [m] : Cathode location (x y z) in csys 1 in the model unit [mm] followed by maximum distance from anode-cathode axis, at which flame kernels are deposited [m] 0 or 1 : 0 if anode and cathode are meshed. One needs to specify the regions that defines the anode and the cathode respectively: 8 : Anode region number defined in mesh 9 : Cathode region number defined in mesh 1 if anode and cathode are NOT meshed. One needs to specify the anode's surface area [m2] as well as its surface temperature [K]. Repeat for cathode's surface area and temperature on next line : Anode surface [m²] and temperature [K] : Cathode surface [m²] and temperature [K] 32

ITRANSK : Flag to define the shape of the flame kernel particles for transition criterion 1 or 2 : 1 =>

33 AKTIM SET-UP AND BEST PRACTICES NOSCK : Flag to turn off subcycle for flame kernel tracking ISHAPED : Flag to define the shape of flame kernels deposit 1 or 2 : 1 => Cylindrical shape / 2 => Spherical shape ITRANSK : Flag to define the shape of the flame kernel particles for transition criterion 1 or 2 : 1 => Cylindrical shape / 2 => Spherical shape With ISHAPED = 1 With ISHAPED = 2 Flame kernels deposit at ignition 33

34 AKTIM SET-UP AND BEST PRACTICES Electrical arc view Cathode boundary region Anode boundary region 34

35 Complex Chemical Kinetic Scheme for ice FUELS Original chemical mechanism for iso-octane from LLNL Enhanced by IFP ( French Petroleum Institute) to Diesel and SI Fuel P, T Engine conditions + EGR Effect Large range of Equivalence Ratio 550 species and 2500 reactions C7H16 + O2 = C7H HO2 C7H16 + O2 = C7H HO2 C7H16 + H = C7H H2 C7H16 + H = C7H H2 C7H16 + OH = C7H H2O C7H16 + OH = C7H H2O C7H16 + HO2 = C7H H2O2 C7H16 + HO2 = C7H H2O2 C7H16 + CH3 = C7H CH4 C7H16 + CH3 = C7H CH4 C7H16 = C7H H C7H16 = C7H H C7H16 = C4H9 + C3H7 C7H O2 = C7H15O2 C7H O2 = C7H15O2 C7H15O2 = C7H14O2H C7H14O2H + O2 = C7H14O2HO2 C7H14O2HO2 = C7KET21 + OH C7KET21 = C5H11CO + CH2O + OH H2O2 + H = H2O + OH C5H11CO = C5H11 + CO CH2O + OH = HCO + H2O C5H11 = C2H5 + C3H6 CH2O + HO2 = HCO + H2O2 C7H15-1 = C2H4 + C5H11 HCO + O2 = HO2 + CO C7H15-2 = CH3 + C6H12 CH4 + O = CH3 + OH C6H12 = C3H7 + C3H5 CH4 + HO2 = CH3 + H2O2 C7H15-2 = C4H9 + C3H6 C2H4 + OH = CH2O + CH3 C7H15-1 = C7H15-2 C2H5 + O2 = C2H4 + HO2 C4H9 = C2H5 + C2H4 C2H3 + O2 = CH2O + HCO C3H7 = C2H4 + CH3 C3H6 = C2H3 + CH3 C3H6 + OH = CH3CHO + CH3 C3H5 + O2 = C3H4 + HO2 C3H4 + OH = C2H3 + CH2O CH3CO + M = CH3 + CO + M CH3CHO + OH = CH3CO + H2O CH3O + CO = CH3 + CO2 CH3O (+M) = CH2O + H (+M) LOW /2.344E E+04/ CH3 + HO2 = CH3O + OH CH3 + O2 = CH2O + OH CO + O + M = CO2 + M CO + OH = CO2 + H HO2 + CO = CO2 + OH H2 + O2 = OH + OH O + OH = O2 + H H + O2 + M = HO2 + M O2/.00/ H2O/.00/ CO/.75/ CO2/1.50/ N2/0.0/ H + O2 + N2 = HO2 + N2 OH + HO2 = H2O + O2 H + HO2 = OH + OH HO2 + HO2 = H2O2 + O2 OH + OH (+M) = H2O2 (+M) LOW / 4.300E / TROE/ / H2/2.00/ H2O/6.00/ CH4/2.00/ CO/1.50/ CO2/2.00/ N2/0.70/ H2O2 + OH = H2O + HO2 C3H8(+M)=C2H5+CH3(+M) LOW / 2.237E / TROE / E E+15/ H2/2.00/ H2O/6.00/ CH4/2.00/ CO/1.50/ CO2/2.00/ N2/.70/ C3H8/4.0/ H+C3H7(+M)<=>C3H8(+M) LOW/ 4.420E / TROE/ / H2/2.00/ H2O/6.00/ CH4/2.00/ CO/1.50/ CO2/2.00/ N2/0.70/ 35

36 Auto-ignition using Tabulated Detailed Chemistry C C1 1 d1 d 2 dc dt 1. A transport equation for enthalpy fluctuation is solved Cool flame ignition delay d1 Fuel consumption C1 after the delay d1 Main auto-ignition delay d2 Reaction progress after the ignition delays d1 et d2 2. A temperature fluctuation is deduced 3. The reaction progress is integrated using a Gaussian PDF s T ~ 2 ' ~ ~ 1 EGR : 0% 36

37 CONCLUSIONS Use of ECFM-3Z model along with standard FIECFM spark ignition model provides good results compared with experiments Variations of octane index and SI timing have been done and can be used to predict knocking limit The combination AKTIM for spark and T.K.I-P.D.F for knock produces very comprehensive and good results The second discretisation scheme for scalars and temperature improve significantly solution on Trimmed polyhedral cells mesh type Need to continue testing and Validations Quick meshing time, even low quality meshes, produced good solution thanks to the high order discretisation 37

Current progress in DARS model development for CFD

Current progress in DARS model development for CFD Harry Lehtiniemi STAR Global Conference 2012 Netherlands 20 March 2012 Application areas Automotive DICI SI PPC Fuel industry Conventional fuels Natural