Post on 21-Aug-2018
transcript
Overview & Perspectives for Internal
Combustion Engine using STAR-CD
Marc ZELLAT
Quick overview of ECFM family models
Examples of validation for Diesel and SI-GDI engines
Introduction to multi-component fuels
Application and validation of multi-component fuel to SI-GDI and Dual fuel engines
– Real multi-component gasoline
– Influence of anti-knock additive in the fuel mixture
– Dual fuel : Diesel/Natural gas combustion
Conclusion and perspectives
TOPICS
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat
A General Schematic View of Spray and Combustion
•c
•Zst
•Diffusion reaction zone
•Air•mixture
•Demoulin & Borghi,
Comb.Flame,129(2002)
•Large scales : τ=k/ε
(integral lenght )
•Small scales : τ=(ν/ε)**0.5
(Kolmogorov lenght)
Mixture fluctuations
Temperature fluctuations
Auto-Ignition
Post-oxidation
Temperature fluctuations
Mixture fluctuations
Kinetic controlled
air + egr
fuel
spray
air + egr
fuel
mixed
spray
air + egr
fuel
mixed
spray
fuel injection into charge (air + egr)
mixing of fuel and charge
ignition in mixed zone
air + egr
fuel
mixed
spray
unburnt burntCombustion in mixed zone
+ Un-mixed in burnt gases
‘EXTENDED COHERENT FLAME - 3 ZONE’
possible fluid states in computational cell
time
THOERETICAL ECFM-CLEH MODEL DESCRIPTION:
ECFM-3Z / ECFM-CLEH models : conceptual framework
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat
PSTOXFDIFFFPMFUMFF ZZZYZ
ECFM-3Z
Zf/unmixed
Zf/premixed Zf/diffusion
Transfer is function of c only
Transfert if Phi > Phi.crit.The diffusion zone is unmixed burnt gases
The post-oxidation is mixed burnt gases
The transfer between zones is from turbulent
mixing and the combustion progresses
SprayECFM-CLEH
THOERETICAL ECFM-CLEH MODEL DESCRIPTION:
ECFM-3Z / ECFM-CLEH concept : Flame structure
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat
THOERETICAL ECFM-CLEH MODEL DESCRIPTION:
ECFM-CLEH model : Fundamental approach of 4 reaction rates
Propagation Diffusion flame
G
F
G
B
Auto-ignition
ECFM model Mixing PDF model
P.D.F : Mixture Fraction
FLUCTUATION
TKI-PDF model
AI-Saturation Coupling
Oxfuel
Tables for LFS
Flame surface density
ITNFS Function
Mixing controlled
reaction rate
Distributed flame with
Pdf on mixing scalar
(look-up table)
Post-Oxidation
Chemical Kinetics
Chemistry controlled
reaction rate
NO Fluctuations
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat
5 operating conditions
point 1 : Full load point 2 : Mid-load
point 3 : Mid-load
point 4 : Low-load point 5 : Low-load
Swirl Level : Flap open/closed
Automotive DIESEL ENGINE B : RESULTS
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat
Emissions
NOx-NORA SOOT CO
0
10
20
30
40
50
60
70
80
90
100
1 2 3 4 5
So
ot
Experiments
STAR-CD
0
10
20
30
40
50
60
70
80
90
100
1 2 3 4 5
CO
Experiments
STAR-CD
0
10
20
30
40
50
60
70
80
90
100
1 2 3 4 5
NO
x
Experiments
STAR-CD(NORA)
Automotive DIESEL ENGINE B : RESULTS
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat
112
146
116
80
0
172
141
79
2010
0
50
100
150
200
-4 -2 0 2 4
CLEH EXPE
7
14
34
44
6
20
15
26
3431
0
5
10
15
20
25
30
35
40
45
50
-4 -2 0 2 4
CLEH EXPE
Injector 1 Injector 2
SOOT
Retarted Injection
Automotive DIESEL ENGINE C : Injector 1 versus Injector 2
Injection timing variation comparison : SOOT
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat
Injector 1 Injector 2
Soot Diameter Soot Diameter
Distribution Distribution
The Soot Sectional Method is capable to
differentiate Soot diameter and Distribution
between injector 1 and injector 2
ENGINE C : Injector 1 versus Injector 2
Injection timing variation comparison :
SOOT Sectional soot model / PDF
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat
GDI-GASOLINE: Real Engine
Wall Guided Multi-hole injector
11
Spray and mixture @ 440 °CA ABDCEquivalence ration around TDC
Red is above ER 1.
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat
In-cylinder pressure history (left) - Apparent Hear Release (right)
Zoom on : In-cylinder Pressure Apparent Rate OF Heat Release
GDI-GASOLINE: Real Engine
Operating point 1 : ECM-CLEH
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat
A single component representative fuel has been used in the examples and validations shown in the previous section
SI-GDI engines are very sensitive to the fuel composition (evaporation process, stratification, Octane number calibration using additives …)
Dual fuel combustion is emerging, especially in combination with Diesel and Natural gas
To get better simulation of the system including combustion chamber, fuel composition and mixture preparation strategy
CD-adapco has extended existing combustion models in STAR-CD to multi-component fuel.
Introduction of Multi-component fuel
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat
Crude
oïl
Light Fraction
Heavy Fraction
Light Gasoline
C5 – C6
RON 60 - 80
Heavy Gasoline
C7 – C10
RON 20 - 50
Unleaded
Gasoline
RON 95 - 98
MON 85 - 87
The refiner must implement processes to improve
the gasoline octane number from natural crudes.
Boiling
Temperature
Heavy GasolineLight Gasoline
AromaticsBenzene
Toluene
Gasoline distillation problem
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat
American Society for Testing and Materials Cooperative Fuel
Research : Distillation process
% volume
Temperature
ASTM procedure
Heated Multi-component Droplet
STAR-Simulation
% volume
Temperature
C1 C1+C2
C1+C2+C3+ C4=anti-knock Agent
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat
The liquid is represented using N components
Vaporization is treated using the discrete approach
For combustion:
– The molecular weight is computed according to local component concentration
taking into account the number of C, H and O in each component
– Same treatment for the Enthalpy of formation and Laminar Flame speed
For Auto-Ignition:
1. When correlation is used:
• Ignition delay and auto-ignition rate are balanced by the Octane (cetane) number of
each component
2. When tables are used:
• Tabulated Kinetic for Ignition technique is used, extracting information directly from
the tables
The multi-component approach with ECFM-3Z combustion model
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat
Gasoline represented by 4 components
Pressure :full cycle Pressure : zoom around TDC
A.R.O.H.R :full cycle A.R.O.H.R : zoom around TDCExperiment
STAR-CD
SI-GDI Wall Guided : MULTI-COMPONENT COMBUSTION
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat
Comparison with baseline gasoline: Same amount of energy is introduced due lower L.HV for Ethanol
Pressure :full cycle A.R.O.H.R : zoom around TDC
Gasoline 4C
Combustion
Laminar flame speed
E85
Combustion
E85 – Combustion
Better homogenization around stoichiometry
Higher Laminar Flame Speed for Ethanol
Higher I.M.E.P
MULTI-COMPONENT – E85 (Mixture Ethanol/Gasoline)
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat
SPRAY
40 CA after start of injection
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat
4 components E85 (Gasoline / Ethanol Mixture)
Operating point 1 KNOCK : Spark Timing VARIATION
Reduced Anti-knock Agent
Chemical Heat Release
Total Chemical Heat Release
Premixed Propagation
Post-oxidation
Premixed Auto-Ignition
Diffusion
S.T=20 btdc
Mean In-cylinder
& Local sensor
S.T=13btdc
GDI-GASOLINE: Spray wall Guided
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat
AI + PM iso-surfaces of Chemical Heat release
Chemical Heat Release
Total Chemical Heat Release
Premixed Propagation
Post-oxidation
Premixed Auto-Ignition
Diffusion
Premixed PropagationPremixed Auto-Ignition
Static (728 °CA) Knock onset (space and time)
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat
CFD Simulations of a Dual Fuel Engine *
Premixed Natural Gas (methane) + Diesel Pilot injection
Tabulated Kinetic for Ignition is used for Auto-Ignition delay
and rate of Auto-ignited consumed fuel
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat*prepared by J.Lim
Case 1
NG % 2.20
Diesel [mg] 27.26
Case 2
NG % 1.72
Diesel [mg] 156.90
Experiment
STAR-CD
Pressure Trace – for case 1 and 2
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat*prepared by J.Lim
Case 2
NG % 1.72
Diesel [mg] 156.90
Case 1
NG % 2.20
Diesel [mg] 27.26
Premixed Auto-Ignition
Diffusion
Propagation
Mixed Mode of Combustion Diesel Mode of Combustion
Chemical heat Release for case 1 and 2
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat*prepared by J.Lim
Single component using a representative specie
– Well established in ECFM combustion models (ECFM-3Z and ECFM-CLEH)
– Good level of prediction for pressure, heat release, wall heat fluxes
– Good level of prediction in emissions : NO, CO and Soot
– The soot sectional method is able to predict soot diameter and distribution
Emergence of multicomponent for mixture preparation and combustion
– ECFM-3Z has been extended to multi-component fuel
– Combustion and fuel composition are seen now as a system
– Ethanol blended duel and Dual duel combustion has extensively been validated
– Possibility to take into account the detailed mechanism – Introducing different fuel (via
External tables)
– CD-adapco is working to provide a tool for tables generation using DARS chemistry solver
– ECFM-CLEH will extended to multi-component fuel in STAR-CD V4.22 (next release)
Conclusion and Perspectives
G. Desoutter, A. Desportes, J. Hira, D. Abouri, M. Zellat