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 2.1 ms 2.5 ms 2.9 ms Liquid Phase Vapor Phase Temperature = 398 K, Pressure = 0.5 MPa

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

LES – multicycle flame development 1 st 2 nd 3 rd 4 th 5 th 6 th 7 th 8 th 9 th 10 th 11 th 12 th 13 th 14 th 15 th 16 th 17 th 18 th 19 th 20 th GRU ppo MO tori Internal Combustion Engine Research Group

LES - 3D Results Insight: Local flow field influence: 16 th slowest 4 th fastest A B A B A B A B GRU ppo MO tori Internal Combustion Engine Research Group

LES – Correlation Coefficient cov( X , Y ) Correlation Coefficient (FSD_transition, Yj)   j ( X , Y ) abs ( ) i j  var( X ) var( Y ) j 1 0.8 0.6 FSD_transition VS Yj (20 cycles) 0.4 0.2 0 ER_local VMAG_local TE_local 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. GRU ppo MO tori 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 Combustion Dome Piston Crown GRU ppo MO tori Internal Combustion Engine Research Group

Effect of Mapped Wall on Knock • 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 Heat Release Rate - Autoignition 1.E+07 1.E+06 1.E+05 1.E+04 [W] 1.E+03 1.E+02 1.E+01 1.E+00 730 740 750 760 770 780 790 800 Crank Angle Uniform Wall - Fast Cycle Uniform Wall - Medium Cycle Uniform Wall - Slow Cycle Mapped Wall - Fast Cycle Mapped Wall - Medium Cycle Mapped Wall - Slow Cycle GRU ppo MO tori Internal Combustion Engine Research Group

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 on 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 707 o CA, Duration 3 o • SOI Gas 711 o CA, duration 16 o

PVM-MF Dual-Fuel Combustion Cylinder pressure and temperature 2.0E+07 1,800 Pressure 1.8E+07 1,600 Temperature 1.6E+07 1,400 1.4E+07 Temperature (K) 1,200 Pressure (Pa) 1.2E+07 1,000 1.0E+07 800 8.0E+06 600 6.0E+06 400 4.0E+06 200 2.0E+06 0.0E+00 0 600 630 660 690 720 750 780 Crankangle (deg)

PVM-MF Dual-Fuel Combustion Heat release rate Diesel Natural gas 2.0E+06 1.8E+06 1.6E+06 Heat release rate (J/sec) 1.4E+06 1.2E+06 1.0E+06 8.0E+05 6.0E+05 4.0E+05 2.0E+05 0.0E+00 700 710 720 730 740 750 760 770 780 790 800 Crankangle (deg)

PVM-MF Dual-Fuel Combustion NG Diesel PV T 708o CA 710o CA 711.5o CA 712o CA

PVM-MF Dual-Fuel Combustion NG Diesel PV T 713o CA 715o CA 717o CA 720o CA

PVM-MF Dual-Fuel Combustion Fuel-1: Diesel Fuel-2: Natural gas

PVM-MF Dual-Fuel Combustion Temperature Combustion progress variable

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 1,700 9.00E-03 Temperature 1,600 8.00E-03 Nox * 10 Emissions mass fraction 1,500 7.00E-03 Soot Temperature (K) 1,400 6.00E-03 CO 1,300 5.00E-03 1,200 4.00E-03 1,100 3.00E-03 1,000 2.00E-03 900 1.00E-03 800 0.00E+00 700 710 720 730 740 750 760 770 780 790 800 Crankangle (deg)

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 Temperature Increment vs Time 40 Temperature Increase [K] 35 Time = 1 ms 30 Time = 5 ms 25 Time = 10 ms 20 15 10 5 0 0.0 1.0 2.0 3.0 Distance from surface [mm] Fluid Cell F Q F FSI 1 Solid Layer 1 2 SSI 3 4 5 contact Solid Layer 2 6 resistance 7 8 B

Spray-induced heat transfer • Cylindrical chamber, stationary mesh • 20 mg of C 8 H 18 • T fuel = 293 K • 20 mg of liquid C 8 H 18 sprayed toward the • Duration = 5 ms bottom wall • Nozzle size = 0.2 mm T wall = 350 K • 3 runs to validate the 1D CHT model • BASELINE : bottom wall at a fixed temperature of 450 K T air = 350 K T wall = 350 K P air = 1 bar • CHT : 5 mm aluminum slab at bottom wall for 3D conjugate heat transfer calculation • 1DCHT : BASELINE mesh with 1D CHT model T wall = 450 K ( BASELINE ) activated at bottom wall Conduction ( CHT ) T bulk = 450 K ( 1DCHT ) • 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%

Spray-induced heat transfer Predicted wall temperature at 15 ms after SOI BASELINE CHT 1DCHT 450 Minimum Wall Temperature [K] Wall l temperatu rature re distrib tributi tion at 15 ms afte ter r SOI: 449 No major differences between the CHT & 1DCHT predictions 448 447 446 BASELINE CHT 445 Minimum temperature on bottom wall as a function of time: 1DCHT 444 No major differences between the CHT & 1DCHT predictions, 0 5 10 15 Time [ms] justifying the use of the 1D CHT model 450 Minimum Wall Temperature [K] 448 446 444 Therm ermal al prope opert rties ies of the he soli lid d has a subst ubstan antial ial effect 442 on wall temper erat atur ure, e, with h low-condu nductivit ivity mater erial ial 440 438 experie perienc ncing ing the he larges rgest tem emper perat atur ure e drop op 2.50_80_1.0k 436 2.50_80_0.5k 434 2.50_80_0.1k 432 0 5 10 15 Time [ms]

Combustion induced heat transfer T wall = 500 K • Cylindrical chamber, stationary mesh T air = 800 K T wall = 500 K • P air = 5 bar Premixed air & C 8 H 18 , ignition at Ω = 2000 rpm chamber center Y C8H18 = 0.0623 • T wall = 500 K ( BASELINE ) 3 runs to validate the 1D CHT Conduction( CHT ) model with 1.25mm BaTiO 3 T bulk = 500 K ( 1DCHT ) (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 t = 5.0 ms t = 15.0 ms t = 2.5 ms conjugate heat transfer calculation • 2 runs to examine the effect of material property on wall BaTiO 3 Aluminum temperature change Density [ kg / m 3 ] 5840 2702 • BaTiO 3 (1.25 mm ) Thermal conductivity [ W / mK ] 2.6 237 • Aluminum (5 mm ) Heat capacity [ J / kgK ] 434 903 Thickness [ mm ] 1.5 5.0