ICE Modeling India Webinar Dec2013

© 2011 ANSYS, Inc. December 19, 20131

In-Cylinder Engine Modeling using ANSYS CFD

December 19th, 2013


Outline

• ICE System in Workbench

• Spray and Combustion Models

• Case-Studies and Best Practices


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


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


Geometry Preparation

Portflow Simulation IC Engine Simulation Sector Simulation

• Geometry

preparation


Meshing

• Predefined meshing templates– Application specific mesh topology, mesh controls

62013 Automotive Simulation

World Congress

Portflow Simulation IC Engine Simulation Sector Simulation


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


Post-processing

Automatic report generation Manual post-processing

8


Demo


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


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


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


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


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.


• 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)


• 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


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


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


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)


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


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


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


• 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


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


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


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.


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.


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


Tutorials and Training Material


27-29 Jan, 2014

ANSYS, Pune


Coming up..

Port flow

Jacket filling

Jacket boiling

Thermal stress

Thermal fatigue


Thank you!

ICE Modeling India Webinar Dec2013

Documents

Transcript of ICE Modeling India Webinar Dec2013