Large Eddy Simulations of Turbulent Spray Combustion in Internal Combustion Engines
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Transcript of Large Eddy Simulations of Turbulent Spray Combustion in Internal Combustion Engines
Large Eddy Simulations of Large Eddy Simulations of Turbulent Spray CombustionTurbulent Spray Combustion
in Internal Combustion in Internal Combustion Engines Engines
Farhad JaberiDepartment of Mechanical Engineering
Michigan State UniversityEast Lansing, Michigan
In-Cylinder Flow: Combination of highly unsteady turbulent flow, separated boundary and shear layers, pressure waves, spray, mixing and combustion in complex geometrical configurations with moving pistons and valves.
CFD & IC Engines: The solver should be able to handle complex geometries with dynamic mesh. LES needs high order numerical method and accurate subgrid turbulence models. For spray, advanced primary and secondary break-up models and fully coupled gas-droplet flow solvers with multi-component droplet evaporation models are needed. Turbulent combustion models with appropriate chemical kinetics mechanisms are also needed.
Previous Works: Mostly based on RANS or low-order LES.
Our Model: LES/FMDF, based on a new Lagrangian-Eulerian-Lagrangian mathematical/numerical methodology.
BackgroundBackground
3
LES/FMDF of Single-Phase Turbulent Reacting LES/FMDF of Single-Phase Turbulent Reacting Flows Flows
Scalar FMDF - A Hybrid Eulerian-Lagrangian Methodology Scalar FMDF - A Hybrid Eulerian-Lagrangian Methodology
Eulerian: Conventional LES equations for velocity, pressure, density and temperature fields
- Deterministic simulations
Lagrangian: Transport equation for FMDF (PDF of SGS temperature and species mass fractions
- Monte Carlo simulations
Coupling of Eulerian and Lagrangian fields: A certain degree of “redundancy” (e.g. for filtered temperature)
COCO22 andand CC77HH1616 Mass FractionsMass Fractions
Pressure IsolevelsPressure Isolevels
Nozzle
Wall
Vorticity Contours & Monte Vorticity Contours & Monte Carlo ParticlesCarlo Particles
Monte Carlo Particles
Kinetics: (I ) reduced kinetics schemes with direct ODE or I SAT solvers, and (I I ) flamelet library with detailed mechanisms or complex reduced schemes.Fuels: methane, propane, decane, kerosene, heptane, J P-10
Filtered continuity and momentum equations via a generalized multi-block high-order finite difference EulerianEulerianscheme for high Reynolds number turbulent flows in complex geometries
Various closures for subgrid stresses
GasdynamicGasdynamicFieldField
Scalar Field Scalar Field (mass fractions(mass fractionsand temperature)and temperature)
Filtered Mass Density Function (FMDF) equation via LagrangianLagrangianMonte Carlo method - I to Eq. for convection, diffusion & reaction
ChemistryChemistry
COCO22 andand CC77HH1616 Mass FractionsMass Fractions
Pressure IsolevelsPressure Isolevels
Nozzle
Wall
Vorticity Contours & Monte Vorticity Contours & Monte Carlo ParticlesCarlo Particles
Monte Carlo Particles
Kinetics: (I ) reduced kinetics schemes with direct ODE or I SAT solvers, and (I I ) flamelet library with detailed mechanisms or complex reduced schemes.Fuels: methane, propane, decane, kerosene, heptane, J P-10
Filtered continuity and momentum equations via a generalized multi-block high-order finite difference EulerianEulerianscheme for high Reynolds number turbulent flows in complex geometries
Various closures for subgrid stresses
GasdynamicGasdynamicFieldField
Scalar Field Scalar Field (mass fractions(mass fractionsand temperature)and temperature)
Filtered Mass Density Function (FMDF) equation via LagrangianLagrangianMonte Carlo method - I to Eq. for convection, diffusion & reaction
ChemistryChemistry
LES/FMDF of a Dump Combustor
Lagrangian Monte Carlo Monte Carlo
ParticlesParticles
Eulerian GridEulerian Grid
Kinetics: (I) global or reduced kinetics models with direct ODE or ISAT solvers, and (II) flamelet
library with detailed mechanisms or complex reduced mechanisms
Fuels considered so far: methane, propane, heptane, octane, decane, kerosene, gasoline,
JP-10 and ethanol
LES of Two-Phase Turbulent Reacting LES of Two-Phase Turbulent Reacting Flows Flows
A New Lagrangian-Eulerian-Lagrangian MethodologyA New Lagrangian-Eulerian-Lagrangian Methodology Filtered continuity and momentum equations via a generalized multi-block high-order finite difference EulerianEulerian scheme for high Reynolds
number turbulent flows in complex geometries
Various closures for subgrid stresses
Gasdynamics FieldGasdynamics Field
Scalar Field Scalar Field (mass fractions(mass fractions
and temperature)and temperature)
Filtered Mass Density Function (FMDF) equation via LagrangianLagrangian Monte Carlo method -
Ito Eq. for convection, diffusion & reaction
ChemistryChemistry
Droplet Field Droplet Field (spray)(spray)
LagrangianLagrangian model for droplet equations with full mass, momentum and energy couplings between phases and a stochastic sub grid
velocity model
• Liquid Fuel Droplets
LES of Two-Phase Turbulent Reacting LES of Two-Phase Turbulent Reacting FlowsFlows
A New Lagrangian-Eulerian-Lagrangian MethodologyA New Lagrangian-Eulerian-Lagrangian Methodology
FMDF Solver
Spray-Controlled Spray-Controlled Dump CombustorDump Combustor
Fuel Injector
Wall
Wall
• Monte Carlo Particles- Eulerian Grid
Eulerian Cell
Mass,Momentum,Scalar Terms from Droplets
LES Solver
Eulerian Finite Difference Grid
Interpolation /Favre Filter
Monte Carlo Particles
FMDF Solver
Filtered Equations - Eulerian
SJu
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J
tJ
i
i
ˆ
uij
ie
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iij
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i SJuuPuu
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Ju
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/ˆ and ,ˆ_____
ffxdxxGtxff
NS
MWRTRTP
1
0^
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Droplet termsDroplet terms
dt
dm
VS p
1
dt
vdm
VS iPui
1
Droplet Equations Lagrangian
FMDF Equation
Lagrangian
xdxxGtxtxtxPL
)()),(,(),(),;( Two-phase subgrid
scalar FMDF:
LLLmi
lLt
iLLi
i
L PSPx
P
xPu
xt
P)(
/~~
dt
dm
Cm
LTT
f
dt
dT p
Lp
vp
p
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Sc
shf
Nuf
Cf
d pDppp 3
,Pr3
,24
Re,
18 32
21
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pp
p Bf
mdt
dm
ii v
dt
dX
dt
dv
dt
dvmLvh
dt
dm
dt
dmCT
dt
dTCm
VS ii
PPP
PPP
LPE )())1
0
Reaction termReaction term
Droplet termsDroplet terms
Reaction termsReaction terms
Eij
i
i
i
i
i SJSJquuPuE
t
JE
t
EJ
ˆˆˆˆˆ
ˆˆ
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SJSJx
MJu
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)( *1ii
d
i vuf
dt
dv
)(/)()(
L
LLPS
PSPS
KHKH RTRT
KH/RT Break-upKH/RT Break-up
Main Features of LES/FMDFMain Features of LES/FMDF Large scale, unsteady, non-universal, geometry- depended quantities are explicitly computed in LES/FMDF
FMDF accounts for the effects of chemical reactions in an exact manner and may be used for various types of chemical reactions (premixed, nonpremixed, slow,fast, endothermic, exothermic, etc.).
LES/FMDF can be implemented via complex chemical kinetics models and is applicable to 3D simulations of hydrocarbon flames in complex geometries.
FMDF contains high order information on sub-grid or small scale fluctuations.
The Lagrangian Monte Carlo solution of the FMDF is free of artificial (diffusion) numerical errors. This is very important in IC engine simulations as overprediction of temperature could cause numerical ignition!
Application of LES/FMDF to Various FlowsApplication of LES/FMDF to Various Flows
Axisymmetric Dump Combustor
Spray Controlled Lean Premixed Square Dump Combustor
IC Engines with Moving Valves/Piston complex cylinder head/piston, spray and combustion
24 Block grid for a 4-valve
Diesel Engine
10 d
eg
ree A
fter
TD
C
Pressure Iso-Levels
Temperature Contours
Wall
Double Swirl Spray Burner
Fuel Injector
62 mm
40 mm
33 mm
19 mm
Inner Air Flow
Outer Air Flow
Atomization gas
Fuel
20mm 70mm
Dyn. Smag-filtered Dyn. Smag-Averaged Smag Cd=0.01 Exp. Data
Axial Velocity Contours
LES of Cold Flow Around a Poppet Valve
Mean axial velocity RMS of axial velocity
x
yGraftieux et al. 2001
Reynolds No = 30,000Mass rate = 0.015 kg/s Dimensions in mm
y
z
5-block LES grid
PistonPiston
5th cycle instantaneousaxial velocity contours m/s
Grid compression or expansion
4-block moving structured grid for LES
Morse et al. (1978)Comp. ratio 3:1 , RPM=200 , Re=2000
Crank angle=144oCrank angle=36o
LES of Flow in a Piston-Cylinder Assembly
Dynamic Smag Smag, Cd=0.01Exp. Data
Mean VelocityMean Velocity RMS of Velocity
CA
=36
oC
A=
144o
Mean values computed by doing both azimuthal and ensemble averaging over cycles
LES of Flow in a Piston-Cylinder Assembly
Rapid Compression Machine – LES/FMDF Predictions
In-CylinderIn-Cylinder
PistonPiston
Simple Piston GrooveSimple Piston Groove
TemperatureTemperatureContoursContours
Hydraulic Chamber Driver ChamberMain Ignition Chamber
Spark Plug
Fuel Injector
Optical Access
piston
piston
piston
Non-Reacting RCM Simulations
Temperature
Pressure
FDFD
MCMC
MCMC
FDFD
Temperature ContoursTemperature Contours
Fuel Mass Fraction ContoursFuel Mass Fraction Contours
Rapid Compression Machine - LES/FMDF Predictions
Reacting Simulations - Consistency between Finite-Difference (FD) and Monte Carlo (MC) values of Temperature and Fuel Mass Fraction
Rapid Compression Machine - LES/FMDF Predictions
Non-Reacting FlowsTemperature Contours
Flat Piston
Non-Reacting FlowsTemperature Contours
Creviced Piston
Reacting Flows without SprayCreviced Piston at 5msec
Reacting Flows with Ethanol Spray
Temperature Ethanol CO2Pisto
nP
iston
Pisto
nP
iston
Pisto
nP
iston
3D Shock Tube Problem – LES/FMDF Predictions3D Shock Tube Problem – LES/FMDF Predictions
3D Shock Tube3D Shock Tube
pp22/p/p11=15=15
pp11
pp22
Two-Block GridTwo-Block Grid
5 MC per cell5 MC per cell 20 MC per cell20 MC per cell 50 MC per cell50 MC per cell
Compressibility effect is included in FMDF-MC . Without Compressible term FMDF-MC results are very erroneous. Number of MC particles per cell is varied but particle number density does not affect the temperature. By increasing the particle number per cell MC densitybecomes smoother but temperature is the same for all cases.
Modeling of Engine Modeling of Engine ConfigurationConfiguration
Spark Plug Exhaust PortInjector
Cylinder Pistonfuel spray
MSU 3-Valve Direct-Injection Spark-Ignition Single-Cylinder Engine
Bore 90 mmStroke 104 mmCompression Ratio 9.8/11Engine Speed 2500 rpm
Intake valves 2 tilted with 5.1o D = 33 mm
Exhaust valve 1 tilted with 5.8o D = 37 mm
MSU 3-Valve DISI Engine:Bore=90mm Stroke=106mm
Direct-Injection Spark-Ignition Engine – LES Direct-Injection Spark-Ignition Engine – LES PredictionsPredictions
18-block Grid
2D Cross Section of 2D Cross Section of 18-block LES Grid18-block LES Grid
Pressure Pressure contourscontours
Valve lift= 11mmPiston velocity=13m/sCrank angle=100o
Valve lift= 5mmPiston velocity=1.5m/sCrank angle=175o
Axial VelocityAxial Velocity
piston
Direct-Injection Spark-Ignition Engine – LES Direct-Injection Spark-Ignition Engine – LES PredictionsPredictions
CA=90 CA=270CA=140
CA=100o CA=220o
piston piston piston
CA=340o
Contours of Evaporated Fuel Mass Fraction
LES/FMDF ofLES/FMDF of 3-Valve DISI Engine with Spray and Combustion 3-Valve DISI Engine with Spray and Combustion
Consistency between Finite Difference (FD) and Monte Carlo (MC) parts of the hybrid LES/FMDF numerical solver
In-Cylinder Temperature Volume Averaged
Crank angle of 350 5 mm from TDC
Instantaneous Values
LES/FMDF Predictions of MSU’s 4-Valve Diesel EngineLES/FMDF Predictions of MSU’s 4-Valve Diesel Engine
Pressure Contours
Temperature Contours
24 Block grid for a 4-valve Diesel Engine
Pressure Iso-Levels
Beginning of Compression
CA=190
LES/FMDF of MSU’s 4-Valve Diesel EngineLES/FMDF of MSU’s 4-Valve Diesel Engine
14o BeforeTDC
6o BeforeTDC
6o AfterTDC
Contours of Evaporated Fuel Mass Fraction and Fuel Droplets
Temperature Contours
LES/FMDF of LES/FMDF of MSU’s 4-Valve MSU’s 4-Valve Diesel EngineDiesel Engine
10 degree After TDC
Temperature Contours
Numerical Simulations of 3-Valve DISI Engine
Without Sprayair mass via cell volume = air mass via ideal gas
With Spray – Valves Closedmass of liquid fuel+evaporated fuel = injected liquid fuel
Variations of mean Temperature
Overall Validation of the model
Simulations of 3-Valve Engine – Spray
In-cylinder Spray Modeling:Initial droplet size, position and
velocity distributionDroplet breakup and collision
modelsMulti-component non-
equilibrium evaporation models
Wall collision and film models
• Stroke: 105.8 mm• Compression Ratio: 11:1• Eight nozzles with cone angle of 8
degree each. Initial SMD: 30 m• Injection Velocity: 50 m/s
Secondary Break-up ModelsSecondary Break-up Models::1) Taylor Analogy Break-up (TAB) -1) Taylor Analogy Break-up (TAB) -
Spring, mass and damperSpring, mass and damper2) Rayleigh-Taylor Break-up (RTB) -2) Rayleigh-Taylor Break-up (RTB) - RT instable wavesRT instable waves3) Kelvin-Helmond Break-up (KHB) -3) Kelvin-Helmond Break-up (KHB) - KH invisid instable wavesKH invisid instable waves4) KH/RT Break-up model4) KH/RT Break-up model
Primary Break-up ModelPrimary Break-up Model: : Parent Parent droplets injected with specific droplets injected with specific velocities and diameters (bold model)velocities and diameters (bold model)
Simulations of 3-Valve Engine – Chemistry
Ethanol
• Detailed Kinetics: e.g. 372 elementary reactions and 57 species for ethanol • Multi-Step Reactions
• Global Mechanisms
• Ignition delays calculated from detailed Mechanism using CHEMKIN for homogeneous 0-D reactor based on equivalence ratio and temperature conditions prevalent in the cell
• By addition of ignition delay, the unphysical phenomenon of autoignition in numerical simulation of SI engines do not occur.
Simulations of 3-Valve DISI Engine – Effects of Fuel
Operating conditions are the same for both fuels
Mixtures are stoichiometric when all fuel is evaporated and mixed
CombustionNo combustion for ethanol fuel
Vaporization No significant evaporation for ethanol
Summary and ConclusionsSummary and Conclusions A robust and affordable LES model is developed for detailed simulations of
various realistic single-cylinder engines: (i) A multi-block compressible LES solver in generalized coordinate system, (ii) Combustion and spray simulations are via a new Lagrangian-Eulerian-
Lagrangian LES/FMDF methodology
Several test cases are simulated with the newly developed models: (i) flow around a poppet valve, (ii) flow in a piston-cylinder assembly, (iii) flow in a single-cylinder three-valve direct-injection spark engine, (iv) flow in a single-cylinder four-valve diesel engine
LES with high-order numerical methods, dynamic SGS models and two-phase FMDF can predict the complex in-cylinder turbulent flows with spray and combustion in realistic engines
Detailed experimental data, under controlled and well defined flow conditions are needed for complete validation of LES/FMDF
LES/FMDF is used for studying effects of (i) chemistry model, (ii) spray model and (iii) various parameters on turbulence, mixing and combustion,