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Modelling of Gasoline Combustion using ECFM-3Z

With STAR-CD V4

Investigation on spark modelling with AKTIM and Knock

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

UL

Tu, Yu

Tb, Yb

S

UNBURNED GASES BURNED GASES

CnHm

CO2

CO

O2

N2

H2O

H2

NO

CnHm

CO2

CO

O2

N2

H2O

H2

NO

H

O

N

OH

UL = f(P,Tu,Yui,..)

dL = f(P,Tu,Tb,..)

FUEL

AIR + EGR

MIXING MODEL

Auto-Ignition

A Hierarchical Approach

ECFM-3Z : Conceptual Framework

3

The Extended Coherent Flame Model-3ZMAJOR HYPOTHESIS

Equilibrium

N2 2 N

O2 2 O

H2 2 H

O2 + H2 2 OH

O2 + 2H2O 4 OH

O2 +2CO 2 CO2

Kinetic

O2 + N2 N + NO

O2 + N O + NO

N + OH H + NO

Reactions are solved using conditioned burnt gases properties

(un-burnt gases for Auto-ignition and laminar flame properties)

CO + OH CO2 + H

Soot

Wisconsin Model

Auto-ignition Delay

Based on experimental

Correlation or tables

4

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

tlltt lSkKK ,,,, d

ITNFS function

Flame Surface Density Transport Equation : 3Z

Misfire limit

1 102 104 106 108 lt/lF

106

104

102

1

v,/SL

Corrugated flamelets

Wrinkled flamelets

Distributed

reaction zones

Da>1,Ka>1

Well-

stirred

reactor

Da<1

Da=1

Ka=1

Ka<1Ret=

1 Engine

combust

ion

Generation due to interaction with turbulence

6

k : turbulent kinetic energy

Sl : Laminar flame speed

δl: Laminar flame thickness

lt : Integral turbulent length scale

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 :

THE TURBULENT BURNING VELOCITY

'*/*2/1

UScCKtUT

ITNFS function7

Experimental data from Abdel-Gayed and Bradley

• Propane mixture : Turbulent burning velocity function of U’

and equivalence ratioQuenching due

Intermittency

8

Sub-models linked to ECFM-3Z

• Spark Ignition

– FI-ECFM (rough standard model)

– AKTIM

• Auto-Ignition (including knock modelling)

– Correlation

– TKI-PDF

9

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

Convected scalar trough a uniform velocity @ 45°

11

Space discretitstaion effect on solution

Scalar and velocity field @time=0

Convected scalar trough a uniform velocity @ 45°

UDS

Min=0 Max=0.3

MARS with Limiters

Min=0 Max=0.99

12

First Order Second Order

Scalar concentration @time=0.01 second !

u

Rc2ye

x

2y

2

2Rc2

v

Rc2xe

x 2 y 2

2Rc2

p p0 2

2Rc2ex

2y

2

Rc2

Ux 10 m/s

Periodicity Periodicityx

y

Numerical Test case Convected vortex in a 2D periodic box

2D structured mesh 80 x 80 13

WHY ? Because:

This test case have EXACT solution.

Domain size, convective velocity, Vortex size can be easily adapted to SITUATION

Numerical Test caseConvected vortex in a 2D periodic box

dt=5e-3s dt=1e-3s dt=1e-4s dt=1e-5s Analytical solution

ALL runs using MARS

Plots show pressure contours

Solution Converges from dt=1e-5s

Compare VERY WELL to the analytical solution

14

Results after 5 turns around time

AND COMPARE TO ANLATYCAL SOLUTION

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

Verify combustion model under simplistic conditions

15

HAMAMOTO TEST CASE Using ECFM-3Z combustion model

HAMAOTO schematic diagram of experimental apparartus

16

Closed Vessel

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

Mesh and : Boundary

18

Walls

Cyclics

Symetry plane

Spark location

• 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

Models

19

Flow : Initial conditions : From measurements

Velocity profile : U2

Turbulent Intensity profile : TI

20

Results (I) : Mean Chamber Pressure and Heat

Release Rate over time

21

Pressure Heat Release *

*Using the method of Lavoie

Results (II) : Flame front position in XZ-plane

22

Experiments :

Time of arrival at ion probe

installed at various location

Predicted:

Maximum Rate of reaction

4.2ms 6.4ms

8.0ms

10.0ms

12ms

4.2ms 6.4ms 8.0ms 10.0ms

12ms

Results (II) : Flame front profiles in XZ-plane

4.2 , 6.4, 8, 10 and 12

ms after Ignition

23

Solid lines : CFD

Dashed lines : Experimental

The CFD contours correspond to

The maximum of Rate of Reaction (Propagation)

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

dYI/dt = YTfu 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 (YI>YTfu)

4) When the delay is reached, the intermediate species concentration is computed as follow :

dYI/dt = 0.1 YI/c /u YFu Where c is the chemical characteristic time

5) The fuel mass fraction evolution is : dYFu /dt = - YFu/c

6) The delay time is evaluated as follow : D = a*(Octa/100)b*(P/(1+XRES))ceTa/Tu with a,b, c and Ta,

some constant model’s constants.

Fuel RON to be specified in the IC setup 24

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

EXAMPLE OF ECFM-3Z GASOLINE CALCULATION : Comparison with experiments

25

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

ECFM-3Z Combustion Simulation :

FIRST OBSERVATIONS

26

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 )

NEW TRENDS

PERFORMANCE / FUEL COMSUMPTION/EMISSION

27

Lagrangian spark ignition model

Arc and Kernel Tracking Ignition Model

• The Aktim model

time0 t2

spark duration ts

2

4

S

laminar to

turbulent

transition phase

fully turbulent

phasespark timing

time t2S2r2

fully turbulent

ECFM model

Aktim + CFM

model

lagrangien

sourceECFM model

Sb,igntign

28

Arc and Kernel Tracking Ignition Model

Model description

Initialization )(tvie

Breakdown phase Spark phase Glow phase

Electrical Circuit

!Breakdown (Inter-electrode voltage)

Ignition

Spark Initialization

Spark deformation by

the mean flow Flame kernels

29

AKTIM : A schematic PRESENTATION

Simplified of coil / Inductive ignition system

Secondary electrical circuit

Ls

Rs

Rs : Resistance

secondary circuit

Ls : Coil Inductance

secondary circuit

Es : Energy in the

secondary circuit

30

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

20000

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]

0.002

BAKT : Coefficient in correlation for gas tension calculation

40460

VAFALL : Tension drop at anode [Volts]

18.75

VCFALL : Tension drop at cathode [Volts]

25231

AKTIM SET-UP AND BEST PRACTICES

HTRANSEL : Heat transfer coefficient between flame kernels and walls

2000

NUMSPK : Number of spark plug considered

1

0.00016667 : Ingition timing [s]

-10.4 0.02 -0.6 0.002 : 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]

-10.1 0.02 -1.2 0.002 : 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.

0.001 473 : Anode surface [m²] and temperature [K]

0.001 473 : Cathode surface [m²] and temperature [K]

32

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

AKTIM SET-UP AND BEST PRACTICES

Electrical arc view

Anode boundary region Cathode boundary region

34

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

Complex Chemical Kinetic Scheme for ice FUELS

C7H16 + O2 = C7H15-1 + HO2

C7H16 + O2 = C7H15-2 + HO2

C7H16 + H = C7H15-1 + H2

C7H16 + H = C7H15-2 + H2

C7H16 + OH = C7H15-1 + H2O

C7H16 + OH = C7H15-2 + H2O

C7H16 + HO2 = C7H15-1 + H2O2

C7H16 + HO2 = C7H15-2 + H2O2

C7H16 + CH3 = C7H15-1 + CH4

C7H16 + CH3 = C7H15-2 + CH4

C7H16 = C7H15-1 + H

C7H16 = C7H15-2 + H

C7H16 = C4H9 + C3H7

C7H15-1 + O2 = C7H15O2

C7H15-2 + O2 = C7H15O2

C7H15O2 = C7H14O2H

C7H14O2H + O2 = C7H14O2HO2

C7H14O2HO2 = C7KET21 + OH

C7KET21 = C5H11CO + CH2O + OH

C5H11CO = C5H11 + CO

C5H11 = C2H5 + C3H6

C7H15-1 = C2H4 + C5H11

C7H15-2 = CH3 + C6H12

C6H12 = C3H7 + C3H5

C7H15-2 = C4H9 + C3H6

C7H15-1 = C7H15-2

C4H9 = C2H5 + C2H4

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+25 -2.7 3.060E+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+18 -.900 -1700.00/

TROE/ .7346 94.00 1756.00 5182.00 /

H2/2.00/ H2O/6.00/ CH4/2.00/ CO/1.50/ CO2/2.00/ N2/0.70/

H2O2 + OH = H2O + HO2

H2O2 + H = H2O + OH

CH2O + OH = HCO + H2O

CH2O + HO2 = HCO + H2O2

HCO + O2 = HO2 + CO

CH4 + O = CH3 + OH

CH4 + HO2 = CH3 + H2O2

C2H4 + OH = CH2O + CH3

C2H5 + O2 = C2H4 + HO2

C2H3 + O2 = CH2O + HCO

C3H8(+M)=C2H5+CH3(+M)

LOW / 2.237E+27 -2.88 67448.0 /

TROE /1.0 1.0E-15 1500.0 1.0E+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+61 -13.545 11357.0/

TROE/ .315 369.0 3285.0 6667.0 /

H2/2.00/ H2O/6.00/ CH4/2.00/ CO/1.50/ CO2/2.00/ N2/0.70/

35

Auto-ignitionusing Tabulated Detailed Chemistry

– 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

1

dt

dc

C1

C

1d

2d

EGR : 0%

~

1~

~ 2'

Ts

1. A transport equation for enthalpy

fluctuation is solved

2. A temperature fluctuation is

deduced

3. The reaction progress is

integrated using a Gaussian PDF

36

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