Post on 24-Jun-2020
Fuchs & Rutland,SAE 980508
Dan HaworthThe Pennsylvania State University
May 2001
GM 6.6L DuramaxOHV V-8
Flynn et al.,SAE 1999-01-0509
Scope Device-scale 3D time-dependent CFD Emphasis on direct-injection diesel engines
Caveat Mainly others work
Acknowledgements Profs. Rolf Reitz and Chris Rutland
Engine Research Center, University of Wisconsin-Madison
Prof. Norbert Peters ITM/RWTH, Aachen, Germany (Stanford University)
Homogeneous Charge Spark Ignition (HCSI) Stratified Charge Compression Ignition (SCCI) Stratified Charge Spark Ignition (SCSI) Homogeneous Charge Compression Ignition (HCCI)
T. Baritaud (Ed.), Multi-Dimensional Simulation of Engine Internal Flows,Oil & Gas Science and Technology: Revue de lInstitut Français du Pétrole,
Vol. 54, No. 2 (1999)
HCSI, SCCI, and SCSI Engines Numerical Methodology Physical Modeling Emissions Prediction
NOX and soot
Turbulent Hydrodynamics Gas-Phase Mixing (Fuel, Air, Residual) Two-Phase Flows (Fuel Sprays) Turbulent Combustion
Heat release Emissions
Other Ignition Heat transfer . . .
Formulation Ensemble averaged equations Two-equation models (mainly k-ε and variants) Wall functions Effective turbulent Prandtl and Schmidt numbers
Strengths Single cycle yields ensemble average (in principle)
Limitations All fluctuations about ensemble mean modeled Cycle-to-cycle variations, transients problematic
Alternatives Higher-order conventional closures (e.g., RSM) Large-eddy simulation (LES)
Formulation Lagrangian particle methods Droplet-distribution-function-based models Physical processes:
Injection/breakup/coalescence/vaporization (single-/multi-component) Gas/liquid coupling (mass, momentum, energy, species) Spray-wall interactions/liquid wall films
Strengths Concentrates particles where needed (adaptive) Enables implementation of comprehensive physical models
Limitations Physics often poorly understood Current models require extensive tuning/calibration to engine, fuel
injector, operating conditions, numerics (e.g., mesh size), . . . Alternatives
Eulerian moment methods
References Veynante & Vervisch, Turbulent combustion
modeling, submitted to Prog. Energy Combust. Sci., 2001. Also in von Karman Institute Lecture Series: Turbulence and Combustion, 2001; to appear.
Haworth, Applications of turbulent combustion modeling, von Karman Institute Lecture Series: Turbulence and Combustion, 2001; to appear.
Saturn 2.2LL-4
If: Steady-state operation Warmed-up engine Homogeneous mixture,
Then: Principal issue is low-speed part-load combustion
efficiency vs. high-speed wide-open-throttle power Turbulent hydrodynamics dominates Intake-port/in-cylinder region can be considered in
isolation
1≈Φ
Discharge Coefficient Flow losses
Swirl and Tumble Large-scale flow structure
Spark-Gap Velocity Flame advection
Late-Compression Turbulence Burn rate
Mixing Fuel/air/residual
Burn-Rate Curves
CD
Swirl orTumble
RealEngines
Inaccessible
Optimum
fasterburn
higher peak power
Scaling (IC Engine) Burn rate is proportional to crankshaft rotational speed
Empirical Evidence Mantzaras, Felton & Bracco SAE 881635 Ziegler et al. SAE 881634
LCSLPLLTLT SSVSuAASS //~/1~// Ω∝′+∝
Unburned Burned
Tu
Tb
<T(x)>
Tb
Tu
T(x)
TDCTmin = 600 K
Tmax = 2000 K
Flame front
Crank Angle Degrees (360=TDC Intake)
Tum
ble
Rat
io
Flamelet Models Represent the Correct Physics for Flame Propagation and Heat Release
Models Are Reasonably Pre-dictive Volumetric efficiency, global flow structure, burn rate Robust nearly homogeneous mixtures
Emissions Usually Are Not Modeled Emissions Models Are Available
CO: equilibrium at specified freeze-out temperature NOX: thermal (Zeldovich, extended Zeldovich) UHC: crevice and oil film adsorption/desorption (non-
combustion processes) PM: negligible
High Dilution (EGR) and/or Highly Lean Detailed Chemistry
UHC speciation, alternative fuels, fuel additives Cycle to Cycle Variations Transient Operating Conditions Ignition Flame/Wall Interactions Crevice Flows Knock
GM 6.6L DuramaxOHV V-8
Fuchs & Rutland,SAE 980508
Flynn et al.,SAE 1999-01-0509
Flynn et al., Diesel combustion: an integrated view combining laser diagnostics, chemical kinetics, and empirical validation, SAE 1999-01-0509 (1999)
T. Baritaud (Ed.), Multi-Dimensional Simulation of Engine Internal Flows,Oil & Gas Science and Technology: Revue de lInstitut Français du Pétrole,
Vol. 54, No. 2 (1999) Barths, Pitsch & Peters (pp. 233-244)
Unsteady non-premixed flamelet model 118 species, 557 reactions for autoignition, heat release, NOX, soot precursors
Belardini & Bertoli (pp. 251-257) Ignition delay correlation, one-step global fuel oxidation (Arrhenius/EBU) Extended Zeldovich NO (Arrhenius/equilibrium/steady-state), six-step soot
(Arrhenius/EBU) Magnusson (pp. 293-296)
EBU heat release Detailed soot model, Zeldovich NO with source terms from flamelet library
Taklanti & Delhaye (pp. 271-277) Shell model autoignition (Arrhenius), EBU heat release Zeldovich NO, simple soot formation/oxidation
Configurations Various engines, sector models, computations begin post-IVC Variations in engine speed, load, SOI, injection history, EGR, fuel type, . . .
Barths, Pitsch & Peters, in T. Baritaud (Ed.), Multi-Dimensional Simulation of Engine Internal Flows, Oil & Gas Science and Technology: Revue de lInstitut Français du Pétrole, Vol. 54, No. 2, pp. 233-244 (1999).
Note: computed NOX values
multiplied by 6.5
Belardini & Bertoli, in T. Baritaud (Ed.), Multi-Dimensional Simulation of Engine Internal Flows, Oil & Gas Science and
Technology: Revue de lInstitut Français du Pétrole, Vol. 54, No. 2, pp. 251-257 (1999).
Magnusson, in T. Baritaud (Ed.), Multi-Dimensional Simulation of Engine Internal Flows, Oil & Gas Science and
Technology: Revue de lInstitut Français du Pétrole, Vol. 54, No. 2, pp. 293-296 (1999).
Taklanti & Delhaye, in T. Baritaud (Ed.), Multi-Dimensional Simulation of Engine Internal Flows, Oil & Gas
Science and Technology: Revue de lInstitut Français du Pétrole, Vol. 54, No. 2, pp. 271-277 (1999).
Reference Yi, Hessel, Zhu & Reitz, SAE 2000-01-1178, 2000
Combustion Modeling Shell autoignition (Arrhenius) Characteristic time combustion (Arrhenius/EBU) Extended Zeldovich NO (Arrhenius/equilibrium/steady state) Two equation soot formation/oxidation
Configuration Heavy-duty DI diesel (Cat 3401) Sector model, calculations begin post-IVC
Approach Model calibration over range of conditions Sensitivity analysis to variations in key engine parameters
SAE 2000-01-1178
SAE 2000-01-1178
SAE 2000-01-1178
Reference Fuchs & Rutland, SAE 980508, 1998
Combustion Modeling Shell autoignition (Arrhenius) Characteristic time combustion (Arrhenius/EBU) Extended Zeldovich NO (Arrhenius/equilibrium/steady state) Two equation soot formation/oxidation
Configuration Heavy-duty DI diesel (Cat 3406) Intake and complete in-cylinder region represented
Approach Variations in valve lift profile, intake-valve shrouds, injection scheme
Fuchs & Rutland, SAE 980508
Case Name Lift Profile ShroudSpeed(rpm)
SOI(deg. ATDC)
InjectionScheme
Standard standard none 1600 351.5 singleSlow slow none 1600 351.5 singleFlat flat none 1600 351.5 single2500 rpm standard none 2500 349.5 singleSwirl standard 1x180o 1600 351.5 singleAnti-Swirl standard 1x180o 1600 351.5 singleTumble standard 2x180o 1600 351.5 singleStandard Split standard none 1600 351.5 doubleSwirl Split standard 1x180o 1600 351.5 double
Swirl TumbleAnti-Swirl
0
10
20
30
40
50
60
355
NO
x (g
/kg
fuel
)
365 375 385 395 405 415 425Crank Angle (deg. ATDC)
StandardSlowFlat2500 rpmSwirlAnti-SwirlTumble
2500 rpm case lacks time to form NOx
Fuchs & Rutland, SAE 980508
X
Standard case Split injection reduces soot emissions
Swirl case Split injection increases soot emissions Corresponds to degraded combustion after 2nd injection
caused by stratification
0
0.5
1
1.5
2
2.5
3
3.5
340
Soot
(g/
kg fu
el)
360 380 400 420 440 460Crank Angle (deg. ATDC)
Swirl SplitStandardStandard SplitSwirl
Fuchs & Rutland, SAE 980508Soot Emissions and Swirl Split Injection
Fuchs & Rutland, SAE 980508Soot Emissions and Swirl Split Injection
Swirl case Soot is stratified 2nd injection aligns with soot cloud
from neighbor plume
fuel - bluesoot - gray
Soot - 15.4%Oxygen - 58.49%
Soot - 44.67%Oxygen - 45.43%
Standard Split Injection Case
Swirl Split Injection Case
373o ATDC: 3o after start of 2nd injection
Reference Peters & Hasse, BMBF Workshop, Germany, 2001
Combustion Modeling Unsteady non-premixed flamelet model (RIF model) >100 species, 500 reactions for autoignition, heat release, NOX,
soot precursors
Configurations Automotive DI diesels: VW 1.9L, Audi 2.5L Sector model, calculations begin post-IVC
Approach Variations in fueling (load) and EGR
Current Models Require Extensive Calibration Current Turbulent Combustion Models Are Not
Literal Representations of the Physics Have proper scaling Have reasonable limiting behaviors
Different Approaches Yield Comparable Levels of Agreement with Engine Measurements
Dominant Combustion Modeling Approaches Equilibrium/Arrhenius/EBU combinations and variants Flamelet models
Current Models Can Be Used Effectively By Experts in Close Concert with Experiments Including NOX and soot emissions
Temporally (and Spatially?) Resolved Engine-Out Velocity, Temperature, Major Species, and Minor Species (Including Pollutants)
Steady-State and Transient Operating Conditions Variations in:
Engine configuration (ports, combustion chamber, valve-lift profiles, fuel injectors, . . .)
Engine operating conditions (load and speed) Fuel composition (alternative fuels, additives, blended
fuels) EGR, injection schedule, . . .
First-Generation Ensemble-AveragedModel Formulations
Fuel-Sprays Diesel Combustion Autoignition, Heat
Release, NOX, and Soot Homogeneous/Nearly Homogeneous
Robust Premixed Flame Propagation Flow Structure and Gas-Phase Mixing
increasinglypre-dictive
Elucidate Physics (with Experiments) Interpolate/Extrapolate (Not Too Far!) from
Established Calibration Points Establish Trends Identify Figures of Merit Develop Correlations for Reduced Models Compute Total and Time-Resolved Engine-Out
Emissions (Steady-State Engine Operation)
Improved Fuel Spray Models Physics Numerical methodology
Next-Generation Turbulent Combustion Models Correct physics of SCCI combustion processes Turbulence/chemistry interactions Flamelet models, PDF methods, and hybrids
Accommodation for Detailed Chemical Kinetics Flamelet models Formal reduction techniques Storage/retrieval schemes
Beyond the Ensemble Average Cycle-to-cycle variations, transient operating conditions Large-eddy simulation
Spatial Filtering Replaces Ensemble Averaging Filtered Moment/Density Function PDEs Have
Essentially Same Form as Ensemble-Averaged Counterparts
Differences Arise From: Filtering being non-commutative with differentiation Filtered fluctuations being non-zero
Differences Often Are Neglected, in Practice Key Physics to be Modeled is at Sub-Filter Scale
Spray and combustion models remain essentially the same Principal difference is specification of turbulence scales