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I C Engine simulation
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© 2011 ANSYS, Inc. December 19, 20131
In-Cylinder Engine Modeling using ANSYS CFD
December 19th, 2013
© 2011 ANSYS, Inc. December 19, 20132
Outline
• ICE System in Workbench
• Spray and Combustion Models
• Case-Studies and Best Practices
© 2011 ANSYS, Inc. December 19, 20133
Ignition Modeling
Combustion Modeling Optimization
Pollutant Modeling
Workflow: Meshing and
Dynamic Mesh Modeling
Near-wall Heat Transfer
Modeling
Flow Modeling
CFD Modeling of IC Engines
Spray Modeling
© 2011 ANSYS, Inc. December 19, 20134
WB ICE System
IC Engine Simulation Tool
Geometry
Preparation
Meshing
Solver Setup
Simulation
Post-
processing
Geometry Motion
Geometry Decomposition
Meshing templates
Mesh controls
Application specific setup
FLUENT solver
HPC simulation
ICE specific post-processing
Report generation
© 2011 ANSYS, Inc. December 19, 20135
Geometry Preparation
Portflow Simulation IC Engine Simulation Sector Simulation
• Geometry
preparation
© 2011 ANSYS, Inc. December 19, 20136
Meshing
• Predefined meshing templates– Application specific mesh topology, mesh controls
62013 Automotive Simulation
World Congress
Portflow Simulation IC Engine Simulation Sector Simulation
© 2011 ANSYS, Inc. December 19, 20137
Solver Setup
• Customized panels
to setup complete IC
engine case– Default parameter settings
for different applications
based on best practise
72013 Automotive Simulation
World Congress
Boundary Conditions
Physics Setup
Engine Data
Monitor Definitions
Solution Initialization
Postprocessing
Chemistry
Combustion
Injection
Ignition
© 2011 ANSYS, Inc. December 19, 20138
Post-processing
Automatic report generation Manual post-processing
8
© 2011 ANSYS, Inc. December 19, 20139
Demo
© 2011 ANSYS, Inc. December 19, 201310
An ANSYS Solution for every Simulation Challenge
High Quality Fuel/Air Mixing
Liquid Fuel Injection
Complex Chemistry
Emission Predictions
Heat Transfer Computation
Configuration Optimization
Advanced Turbulence Models (RANS, SAS, LES)
DPM tracking, Advanced Break-Up Models
Complete Array of Turbulent Chemistry Models
Post-Processing and Coupled Pollutant Models
Advanced Wall Functions and Turbulence Models
Parametric Simulation, Design Exploration
© 2011 ANSYS, Inc. December 19, 201311
Spray Models
FLUENT 14 FLUENT 14.5
Improved wall-film heat transfer
0.00E+00
5.00E-04
1.00E-03
1.50E-03
2.00E-03
2.50E-03
0 1 2 3 4 5
Dp
(m
)
time (s)
Diffusion-controlled
Convection Diffusion-controlled
Experimental Data – symbols
Improved droplet evaporation laws
Single droplet experiment of Wong-Lin
φφ linconstDPMSSS +=,
Source term linearization
Volume fraction
standard average
Volume fraction
node based average
Node-based source averaging
KH-RT breakup model
© 2011 ANSYS, Inc. December 19, 201312
Multi-Component Droplet Evaporation
• Assume that the evaporation rate of component i is proportional to the
component’s vapour pressure ����
• Multi-component droplet evaporation model comparison with optical levitation
experiments of J. Wills (PhD thesis, Univ. of Stuttgart, 2005) : Red
= 0
total
ivap
i
i
i
p
p
dtdm
dtdm ,
/
/=
∑
Diameter variation as f(t) for binary mixture of
hydrocarbonsDiameter variation for ternary mixture
© 2011 ANSYS, Inc. December 19, 201313
Spray Modeling
Only ΣΣΣΣ - Y
ΣΣΣΣ - Y + DPM
Only DPM
Solve for Σ-Y
for Liquid Phase and RANS
equations
Removal from Eulerian And Injection of DPM
Prepare Inputs forLagrangian Phase
Identify the Droplets in Eulerian Phase
2
~
)( Σ−Σ++∂
∂
Σ∂∂
=∂
Σ∂+
∂
Σ∂s
i
i
s
i
i VaAx
xD
x
u
t
i
i
i
i
x
Yu
xdt
Y Yu∂
∂−=
∂
∂+
∂~
''
~~~
ρρρ
Σ
ELSA
VaporisationVaporisation
Vaporisation and
secondary breakup
Vaporisation and
secondary breakupCombustionCombustion
ELSA
Y
Σ-Y
• Approaches
– Full VOF
• Prohibitively CPU expensive
– Full DPM
• Require inputs like spray angle
– ELSA Σ-Y + DPM
• UDF Based
• Modest cpu requirement
• Suitable for IC applications with low liquid to gas density ratio
© 2011 ANSYS, Inc. December 19, 201314
Combustion Models (CI Engines)
• Diesel Unsteady Flamelet model
– Solves for 1D Flamelet equation simultaneously with other transport equation.
– Flamlets generation using CHEMKIN files
– The multiple flamelets allow to model:
• Split injections
• Lifted spray flames
• EGR modeling with mixture fraction
• Laminar Finite Rate model– Solves individual species transport
equations.
– Reactions can be defined using CHEMKIN file
– Calculation speed can be increased using Chemistry Agglomeration features.
© 2011 ANSYS, Inc. December 19, 201315
• Partially premixed combustion model
– Combine non-premixed (f) and premixed (c) models
– Progress variable formulation– C-equation model – G-equation model
– Chemistry Tabulation– Equilibrium Chemistry
– Flame Speed Models– Zimont Flame Speed– Peters Flame Speed
– Compressibility Effects
• Laminar Finite Rate model– Solves individual species transport
equations.
– Reactions can be defined using CHEMKIN file
– Calculation speed can be increased using Chemistry Agglomeration features.
Combustion Models (SI Engines)
© 2011 ANSYS, Inc. December 19, 201316
• Spherical flame assumed
• Solve an ODE for the spark flame radius
– Four spark flame speed models:
• Turbulent Curvature, Turbulent Length, Herweg-Maly, Laminar
• Flame propagates to a transition diameter
– Turbulent length scale
• Reaction progress in spherical transition volume ramped up gradually in time
• Inputs:
– Spark location and initial radius
– Since gas behind flame front is equilibrated, no energy input is required for ignition
Spark Model
© 2011 ANSYS, Inc. December 19, 201317
Efficient Chemistry Acceleration
IN-SITU ADAPTIVE TABULATION
Store Reaction Mappings in an ISAT table
Retrieve Reaction rates when needed
Up to 100 Speed-Up Factor
CHEMISTRY AGGLOMERATION
Agglomerate cells of similar Composition
Call ISAT on Agglomerated Cells
Map Reaction Step back to Original Cells
DIMENSION REDUCTION
User selects the transported Species
Calculate the remaining unrepresented species
using constrained chemical equilibrium
DYNAMIC MECHANISM REDUCTION
Dynamically finds out the optimized reaction
mechanism
Each control volume can have its unique
reaction mechanism
Uses DRG algorithm to reduce the mechanism
© 2011 ANSYS, Inc. December 19, 201318
NOx Model
Volatiles, gaseous and
liquid fuel nitrogen
HCN and/or NH3N2
NOChar nitrogen
NOx emission
NO
O2
Hydrocarbon
radicals, CHi
NO(reburn)
N2(prompt)
N2OCombustion air O2 and N2
© 2011 ANSYS, Inc. December 19, 201319
Soot Modeling
• Moos-Brokes model– Solve transport equations for the
soot mass fraction and (normalized)
number density
– Moss-Brookes-Hall extension for
higher hydrocarbon (the original
model has been developed for CH4)
© 2011 ANSYS, Inc. December 19, 201320
Homogeneous Combustion in a SI Engine
Engine Specifications
Engine Type 4-Stroke, 4-Valve, SI
Chamber Geometry Pentroof
Fueling type Spray-guided direct-
injection
Displacement 696 cm3
Compression Ratio 12:1
Injection Pressure 11 MPa (typical)
• Measurement data
– High-speed in-cylinder measurements• Pressure, temperature
• Cylinder head &liner temperature
– Injector characterization• Spray penetration
• Diameter and velocity distribution
• Measurements
– Motored operation
– Fired homogeneous (fully vaporized) spark-ignition operation with premixed air/fuel mixtures
– Direct-injection spark-ignition operation
– Injector characterization
© 2011 ANSYS, Inc. December 19, 201321
INTAKE: P(t), T=Const.
Mean f=0.06052 (phi =0.97)
EXHAUST: P, T=Const.
CHAMBER: Inert =1,
f=0.06052
Wisconsin Homogeneous Combustion: SI Engine
© 2011 ANSYS, Inc. December 19, 201322
Wisconsin Homogeneous Combustion: SI Engine
0
10
20
30
40
50
60
70
80
90
100
0
5
10
15
20
25
320 370 420 470 520 570 620 670 720 770
AH
RR
, J/
CA
Pre
ssu
re,
Ba
r
PM_2.5_0.97 Experimental AHRR AHRR-Exp
IVO EVC IVC SPARK
Spark Timing: 2.5 bTDC
RPM: 2000
Intake Air: 80 kpa
Equivalence Ratio: 0.97
CFD Fuel: Iso-octane
CFD Model: G-equation
© 2011 ANSYS, Inc. December 19, 201323
• DI Diesel Engine fuelled with Biodiesel [1]
• Hemispherical Shape Piston Bowl
• Modified Re-entrant piston Bowls
• Central PIP height Varied
All other parameters like compression ratio, bowl volume, fuel injection properties
kept same.
Bowl Shape Optimization for a Bio-Diesel Engine
[1] Brakora, Jessica L., "A Comprehensive Combustion Model for Biodiesel-Fueled Engine Simulations", PhD Dissertation, University of Wisconsin-
Madison, 2012.
“Computational Fluid Dynamic Modeling of In-Cylinder Air Flow, Biodiesel Combustion in a Direct Injection Diesel
Engine”, Ishan Verma, Alok Khaware, 23rd NCICEC, Surat, 13th-16th Dec
© 2011 ANSYS, Inc. December 19, 201324
Pressure- Traces
12
32
52
72
92
112
132
152
680 700 720 740 760 780
Pre
ssu
re,
Ba
r
Crank Angle, deg
BASELINE Piston ONE Piston TWO Piston THREE
© 2011 ANSYS, Inc. December 19, 201325
© 2011 ANSYS, Inc. December 19, 201326
Cylinder Head Temperature Prediction
Temperature profile on
the firedeck
Time-averaged Heat
Flux profile on cylinder
head
Steady state conjugate heat
transfer of cylinder head
Transient in-cylinder
combustion simulation in
diesel engine
Iterative Process
© 2011 ANSYS, Inc. December 19, 201327
Solver Details
• Dynamic Mesh (Layering) to account for piston and valve motion.
• SST-kw model for turbulence modeling.
• Discrete Phase Modeling for Sprays
• Spherical drag model
• Wall-film boundary condition
• KH-RT breakup model
• Solid-cone injection type
• Turbulent dispersion of particles
• Stochastic collision model
• Temperature dependent liquid properties (especially vapor pressure and surface tension)
• Diesel Unsteady Flamelet Model (DUFL) with reduced n-heptane mechanism*
• Solver Settings
• Unsteady segregated solver with cell-based gradients
• P-V Coupling : PISO
• Pressure : PRESTO!
• Transport Equations : 2nd order
* University of Wisconsin-Madison, Engine Research Center, n-heptane reaction mechanism (29
species and 52 reactions), SAE 2004-01-0558.
© 2011 ANSYS, Inc. December 19, 201328
Results
S. Shrivastava, P. Mandloi, A. Walavalkar 'Modeling IC Engine Thermal Management using ANSYS CFD' at IMEM
User’s Group Meeting at the SAE Congress, April 23, 2012. Detroit, MI, USA
Transient IC runs performed on dual-quad core machine with 32
GB RAM and AMD 64 bit processors with 2.8 GHz clock-speed,
using 16 nodes.
© 2011 ANSYS, Inc. December 19, 201329
Summary
• ICE System in Workbench provides a consistent and
easy-to-use workflow for setting up IC engine problem
• Spray and Combustion Models cover a wide range of
applicability of engine systems and their operating
conditions
• Case-Studies and Best Practices demonstrate the
validation of IC engine modeling capabilities in ANSYS
CFD
© 2011 ANSYS, Inc. December 19, 201330
Tutorials and Training Material
© 2011 ANSYS, Inc. December 19, 201331
27-29 Jan, 2014
ANSYS, Pune
© 2011 ANSYS, Inc. December 19, 201332
Coming up..
Port flow
Jacket filling
Jacket boiling
Thermal stress
Thermal fatigue
© 2011 ANSYS, Inc. December 19, 201333
Thank you!