Capabilities Richard Johns & Gerald Schmidt Contents Brief - - PowerPoint PPT Presentation

In-Cylinder Engine Calculations: New Features and Upcoming Capabilities

Richard Johns & Gerald Schmidt

Contents

• Brief Review of STAR-CD/es-ice v4.20
• Combustion Models
• Spray Models
• LES
• New Physics Developments in v4.22
• Combustion Models – PVM-MF
• Crank-angle resolved Conjugate Heat Transfer
• New Meshing Technologies
• Morphing/remeshing/mapping
• Overset Mesh

Combustion Models

• Combustion Models
• ECFM-3Z - Multi-fuel capability
• ECFM-CLEH - further development of emissions models -

NORA NOx model, CO, soot

• PVM-MF - First Release
• Open Format for Fuel Libraries – User chemistry mechanism
• Why do we have 3 combustion models?
• ECFM-CLEH will become the successor to ECFM-3Z
• PVM-MF combines the G-equation and flamelet concepts

Spray Models – Wall Impingement

• Spray Models - Senda Droplet-Wall Interaction Model
• Developed by Prof. Senda at Doshisha University, Japan
• Covers three boiling heat transfer regimes with distinct

submodels and extensive validation

Temperature = 398 K, Pressure = 0.5 MPa

2.1 ms 2.5 ms 2.9 ms

Liquid Phase Vapor Phase

LES

• LES – Collaboration with University of Modena
• Focus on real-engine application:
• Cycle-by-cycle variations – COV prediction
• Ignition process – AKTIM and ISSIM models
• Knock sensitivity – critical for highly rated and

downsized engines

• Effect of non-uniform wall temperature – CHT

solution

GRUppoMOtori

Internal Combustion Engine Research Group

LES – multicycle flame development

2 nd 3 rd 1 st 4 th 5 th 7 th 8 th 6 th 9 th 10 th 12 th 13 th 11 th 14 th 15 th 17 th 18 th 16 th 19 th 20 th

GRUppoMOtori

Internal Combustion Engine Research Group

Local flow field influence: 4th fastest 16th slowest

LES - 3D Results Insight:

A B A B A B A B

GRUppoMOtori

Internal Combustion Engine Research Group

LES – Correlation Coefficient

) ) var( ) var( ) , cov( ( ) , (

j j j i

Y X Y X abs Y X   

0.2 0.4 0.6 0.8 1 ER_local VMAG_local TE_local

Correlation Coefficient (FSD_transition, Yj)

FSD_transition VS Yj (20 cycles)

CCV itself relevantly depends on the FSD_transition CCV. This parameter (thus the transition between the ignition model and the FSD equation) is mostly influenced by equivalence ratio and velocity fields close to the spark plug at the spark time occurrence.

GRUppoMOtori

Internal Combustion Engine Research Group

Mapped Wall Temperature

• Conjugate Heat Transfer (CHT)

analyses in Star-CCM+ to calculate the local heat transfer

• A realistic point-wise wall thermal field

is applied to LES knocking combustion Mapped Wall Temperatures

Piston Crown Combustion Dome

GRUppoMOtori

Internal Combustion Engine Research Group

Effect of Mapped Wall on Knock

1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 730 740 750 760 770 780 790 800 [W] Crank Angle

Heat Release Rate - Autoignition

Uniform Wall - Fast Cycle Uniform Wall - Medium Cycle Uniform Wall - Slow Cycle Mapped Wall - Fast Cycle Mapped Wall - Medium Cycle Mapped Wall - Slow Cycle

• A more accurate prediction of knock is obtained
• Knock onset and intensity prediction benefit from the point-wise

thermal field SAE Paper 2013-01-1088

Combustion – PVM-MF

• The PVM-MF model has been enhanced particularly for dual-

fuel combustion

• An example is shown here of diesel/gas combustion based
• n the Westport combustion system

Picture source: http://www.westport.com/is/core-technologies/combustion

PVM-MF Dual-Fuel Combustion

• Engine Details

– Bore 130 – Stroke 150 – Conrod 260 – Compression ratio 18

• Operating Condition

– Engine speed 1500 rev/min – AFR-NG 30.3, AFR-Diesel 273 – EGR 2.5% – Fuel injection

• SOI Diesel 707oCA, Duration 3o
• SOI Gas 711oCA, duration 16o

Cylinder pressure and temperature

200 400 600 800 1,000 1,200 1,400 1,600 1,800 0.0E+00 2.0E+06 4.0E+06 6.0E+06 8.0E+06 1.0E+07 1.2E+07 1.4E+07 1.6E+07 1.8E+07 2.0E+07 600 630 660 690 720 750 780

Temperature (K) Pressure (Pa) Crankangle (deg) Pressure Temperature

PVM-MF Dual-Fuel Combustion

Heat release rate

0.0E+00 2.0E+05 4.0E+05 6.0E+05 8.0E+05 1.0E+06 1.2E+06 1.4E+06 1.6E+06 1.8E+06 2.0E+06 700 710 720 730 740 750 760 770 780 790 800

Heat release rate (J/sec) Crankangle (deg)

Diesel Natural gas

PVM-MF Dual-Fuel Combustion

711.5oCA

Diesel PV NG T

712oCA 710oCA 708oCA

PVM-MF Dual-Fuel Combustion

717oCA

Diesel PV NG T

720oCA 715oCA 713oCA

PVM-MF Dual-Fuel Combustion

Fuel-1: Diesel Fuel-2: Natural gas

PVM-MF Dual-Fuel Combustion

Combustion progress variable Temperature

PVM-MF Dual-Fuel Combustion

• Emissions models available in PVM-MF:

– Thermal Nitric Oxide

• Extended Zeldovich Mechanism (Daulch et al. 1973 , Flower et al.1975,

Monat et al. 1979)

– NO mass fraction (used in example)

• Flamelet Library (Lartsson et al. 1998)

– NO mass fraction

– Soot

• Das-Houtz-Reitz (1999) model implemented within ECFM-3Z

– Soot Mass (used in example)

• Moment Method (Lartsson et al. 1998)

– Soot Number Density – Soot Volume Fraction – Soot Surface Density – Soot Mean Diameter

– Carbon Monoxide CO (Hautman et al. 1981)

• CO-CO2 Kinetics Chemistry implemented within ECFM-3Z

– CO mass fraction(used in example)

PVM-MF Dual-Fuel Combustion

Emissions

0.00E+00 1.00E-03 2.00E-03 3.00E-03 4.00E-03 5.00E-03 6.00E-03 7.00E-03 8.00E-03 9.00E-03 800 900 1,000 1,100 1,200 1,300 1,400 1,500 1,600 1,700 700 710 720 730 740 750 760 770 780 790 800

Emissions mass fraction Temperature (K) Crankangle (deg) Temperature Nox * 10 Soot CO

PVM-MF Dual-Fuel Combustion

Crank-angle resolved Conjugate Heat Transfer

Purpose of the Model:

• To have an easy-to-use capability for crank-angle resolved

changes in surface temperature. Important for:

• Spray impingement – reduced surface temperature

and hence fuel evaporation rate which affects mixture distribution

• Surface coatings of high thermal resistance
• Easy-to-use by specifying a few simple parameters about

the near-surface conducting layer – 1D heat flow assumption does not need an additional mesh

Crank-angle resolved Conjugate Heat Transfer

Fluid Cell Solid Layer 1 Solid Layer 2 FSI SSI

contact resistance

QF

F

1 2 3 4 5 6 7 8

B 5 10 15 20 25 30 35 40 0.0 1.0 2.0 3.0

Temperature Increase [K] Distance from surface [mm]

Temperature Increment vs Time

Time = 1 ms Time = 5 ms Time = 10 ms

Spray-induced heat transfer

• Cylindrical chamber, stationary mesh
• 20 mg of liquid C8H18 sprayed toward the

bottom wall

• 3 runs to validate the 1D CHT model
• BASELINE: bottom wall at a fixed temperature of

450 K

• CHT: 5 mm aluminum slab at bottom wall for 3D

conjugate heat transfer calculation

• 1DCHT: BASELINE mesh with 1D CHT model

activated at bottom wall

• 3 runs to examine the effect of material

property on wall temperature change

• 1.0k: standard aluminum property
• 0.5k: conductivity reduced by 50%
• 0.1k: conductivity reduced by 90%
• 20 mg of C8H18
• Tfuel = 293 K
• Duration = 5 ms
• Nozzle size = 0.2 mm

Tair= 350 K Pair= 1 bar Twall = 350 K Twall = 350 K Twall= 450 K (BASELINE) Conduction (CHT) Tbulk = 450 K (1DCHT)

Minimum temperature on bottom wall as a function of time: No major differences between the CHT & 1DCHT predictions, justifying the use of the 1D CHT model

444 445 446 447 448 449 450 5 10 15 Minimum Wall Temperature [K] Time [ms]

BASELINE CHT 1DCHT

BASELINE CHT 1DCHT

Predicted wall temperature at 15 ms after SOI

432 434 436 438 440 442 444 446 448 450 5 10 15 Minimum Wall Temperature [K] Time [ms]

2.50_80_1.0k 2.50_80_0.5k 2.50_80_0.1k

Therm ermal al prope

• pert

rties ies of the he soli lid d has a subst ubstan antial ial effect

• n wall temper

erat atur ure, e, with h low-condu nductivit ivity mater erial ial experie perienc ncing ing the he larges rgest tem emper perat atur ure e drop

• p

Wall l temperatu rature re distrib tributi tion at 15 ms afte ter r SOI: No major differences between the CHT & 1DCHT predictions

Spray-induced heat transfer

Combustion induced heat transfer

• Cylindrical chamber, stationary

mesh

• Premixed air & C8H18, ignition at

chamber center

• 3 runs to validate the 1D CHT

model with 1.25mm BaTiO3 (barium titanate) layer

• BASELINE: bottom wall at a fixed

temperature of 500 K

• 1DCHT: BASELINE mesh with 1D CHT

model activated at bottom wall

• CHT: slab at bottom wall for 3D

conjugate heat transfer calculation

• 2 runs to examine the effect of

material property on wall temperature change

• BaTiO3 (1.25 mm)
• Aluminum (5 mm)

Tair= 800 K Pair= 5 bar Ω = 2000 rpm YC8H18 = 0.0623 Twall= 500 K (BASELINE) Conduction(CHT) Tbulk = 500 K (1DCHT) Twall = 500 K Twall = 500 K

BaTiO3 Aluminum

Density [kg/m3] 5840 2702 Thermal conductivity [W/mK] 2.6 237 Heat capacity [J/kgK] 434 903 Thickness [mm] 1.5 5.0

t = 2.5 ms t = 5.0 ms t = 15.0 ms

Maximum wall temperature increase as a function of time: No major differences between the CHT & 1DCHT predictions; verifying the validity of the 1D CHT model

500.0 502.0 504.0 506.0 508.0 510.0 512.0 514.0 5 10 15 20 25 30 35 40 45 50

• Max. Wall Temperature [K]

Time [ms] 1DCHT_BaTiO3_1.25mm 1DCHT_Al_5.00mm

BASELINE CHT 1DCHT

Predicted wall temperature 25 ms after SOI

500.0 502.0 504.0 506.0 508.0 510.0 512.0 514.0 5 10 15 20 25 30 35 40 45 50

• Max. Wall Temperature [K]

Time [ms]

Maximum Wall Temperature vs Time

BASELINE CHT_1.25mm 1DCHT_1.25mm

Thermal properties of the solid has a strong effect on wall temperature increase, must be properly accounted for in

• rder to achieve accurate combustion and emissions

predictions Wall temperature distribution 25 ms after SOI: No major differences between the CHT & 1DCHT predictions

Combustion induced heat transfer

• Multiple solid layers with contact resistance at solid-solid interfaces
• 1D energy balance on each solid cell
• Boundary conditions:
• Given heat flux (QF) from the fluid side (computed inside STAR-CD)
• Specified bulk temperature (TB) at the solid side (specified by user)
• Resulting equations give a tri-diagonal system which is solved very

efficiently

• Works with all existing STAR-CD models:
• Liquid Film
• Spray
• Combustion
• Boiling etc.
• Available early 2014

Summary of 1D CHT Model

• Meshing technology is critical to the ease-of-use

and accuracy of in-cylinder calculations

• In addition to the existing es-ice meshing

methodology new methods have been developed for use with IC Engine flows

• The options that will become available are:
• More automation of the existing es-ice meshing
• Technology based on morphing/remeshing/mapping –

available in 2014

• Overset mesh – STAR-CCM+ technology

Meshing for IC Engines

Period: TDC > 30o ABDC (210o) Total of 6 meshes Max cells ~ 1.5M at BDC Period: TDC > 30o ABDC (210o) Scalar Flow & Mixing

Morphing/Remeshing/Mapping - Setup

Mesh generated at this time Mesh morphed in - time Mesh morphed in + time Solution mapped to next mesh

• Different types of meshes may be used at different

stages of the calculation

Meshing Options

Constrained Polyhedra

Core Cartesian Mesh Prism Layers Polyhedral Mesh Local Coordinate Systems and Local Mesh Refinement Variable number

• f prism layers

Example: 4-valve Gasoline Engine

Details around valve at low and high lifts

2-valve Gasoline with polyhedral mesh

2-valve Gasoline with polyhedral mesh

Inclusion of Spray-Adapted Mesh

The same concept can be used to embed a local coordinate system for eg a spray-adapted mesh in a gasoline engine Selected morphing used to control mesh motion

Gasoline Gasoline Spr Spray ay-Ada Adapted pted Mesh Mesh

Period: TDC > 30o ABDC (210o) Spray-adapted mesh between 80o BBDC > 50o BBDC Total of 7 meshes Max cells ~ 1.5M at BDC

Gasoline Spray-Adapted Mesh

Scalar Field from Intake Flow

Overset Mesh

ICE in STAR-CCM+

• CD-adapco is accelerating the development of full

Internal Combustion Engine capabilities in STAR-CCM+

• Development and

Support of ICE in STAR-CD will continue indefinitely

Summary

• Significant Developments in all key areas:
• Combustion models – multi-fuel, emissions developments
• Fuels – open format for fuel chemistry libraries
• Sprays – wall impingement models
• Crank-angle resolved conjugate heat transfer
• LES
• New automated and accurate meshing technologies
• Accelerated development of full ICE capability in

STAR-CCM+