modelling of gasoline combustion using ecfm-3z with ... , 6.4, 8, 10 and 12 ms after ignition 23...
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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
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