Gasoline & Diesel Engineering Fluid Simulation Tools

1. Gasoline & Diesel EngineeringFluid Simulation Tools Ricardo Japan TSA Visits November 2005 RD.05/406501.1

2. Agenda • Background • Combustion System Simulation • Intake, Exhaust and Aftertreatment System • Engine Thermal Modelling • Crankcase Breathing • Vehicle Simulation

3. Agenda • Background • Combustion System Simulation • Intake, Exhaust and Aftertreatment System • Engine Thermal Modelling • Crankcase Breathing • Vehicle Simulation

4. Background • Simulation technology has ability to reduce product development cycle significantly • Principal requirements are: • Robust analysis methodology capable of capturing major physical parameters through direct modelling or correlated database information • Rapid analysis toolset to provide engineering direction for component / system / powertrain development • Validated modelling approach allowing predictive application to engineering projects Presentation will outline fluid simulation application processes to allow technologies application on powertrain development projects leading to reduced product development cycles

5. Agenda • Background • Combustion System Simulation • Intake, Exhaust and Aftertreatment System • Engine Thermal Modelling • Crankcase Breathing • Vehicle Simulation

6. Combustion System Simulation • Combustion system tools and techniques research forms primary stages in application of simulation to combustion system development • Tools and techniques allow predictive application of some modelling technology to development Experimental techniques to measure fundamental physical processes for basic validation of CFD codes Ongoing detailed tools and techniques programme measuring gasoline and diesel fuel spray behaviour under realistic engine operating conditions Development of modelling processes following fundamental validation for application to engineering programmes Continual process of methodology evolution and development with validation against test programmes where applicable

7. Optical Engine Mie Camera Laser Sheet Viewing Annulus LIF Camera Fuel Spray Measurement and Validation • Gasoline spray and mixture measurement • Quiescent fuel spray characterisation • MIE scattering measurements in motored engine • homogeneous operation • stratified operation • Quantitative LIF measurement • Diesel spray and mixture measurement • Quiescent spray bomb characterisation • Ricardo Diesel spray rig • Provides cylinder conditions close to engine cylinder conditions • Validation techniques applied to VECTIS and Star CD

8. Combustion System Gasoline Engine Application Process • Gasoline combustion system design support • 3D CFD simulation applications include • PFI and GDI combustion system development • Cold start mixture preparation simulation • Combustion and emissions prediction for conventional or HCCI operation • Knock prediction development

9. Gasoline Engine Application Process • Principal issues for simulation focus • Geometry definition • Model exactly what will or has been tested • Spray modelling • Injector characterisation and spray match • Wall film prediction • Boundary conditions • Flow conditions (high speed pressure data from 1D / test) • Thermal boundary conditions

10. Modelling tools Four-stroke engines Two-stroke engines Conventional engines Conventional engines VECTIS WAVE Optical engines Optical engines 1-D 3-D Combustion system design Combustion System Case Study – Gasoline HCCI • Ricardo Gasoline Engine HCCI combustion Research

11. Combustion System Case Study – Gasoline HCCI • Uncertainties encountered in the modeling study of HCCI engine combustion • Charge inhomogeneity • Thermal inhomogeneity • Composition inhomogeneity • Trapped conditions • High percentage of trapped residuals, difficult to measure experimentally • Simulation strategy • Full 3-D CFD simulation to cover all processes included in the engine cycle • Multi-cycle simulation approach to eliminate the uncertainties regarding trapped conditions • Compact ignition and combustion models for computational efficiency

12. TDC EVO IVC CA EVC IVO SOI BDC Combustion System Case Study - 2-stroke Gasoline HCCI • Engine Configuration • Upright intake ports • 4 poppet valves • Pentroof combustion chamber • Flat piston • Swept volume 325cc • Compression ratio 9.0 • Loop scavenging • Valve and injection timing

13. 4.5 4.0 C 3.5 HCCI Operation 3.0 IMEP [bar] B 2.5 A 2.0 D 1.5 1.0 1000 1500 2000 2500 3000 3500 Engine Speed [rev/min] Combustion System Case Study - 2-stroke - Simulation Cases

14. Combustion System Case Study – 2-stroke – Simulation Approach • Start position after the end of combustion but before exhaust valve opening • Initial cylinder pressure from experimental measurement • other initial conditions estimated • Pressure boundary conditions applied at the intake port entrance and exhaust port exit • Boundary pressures taken from the recorded dynamic pressures from engine test • Multi-cycle combustion simulation performed until a cyclically-converged solution obtained • Ignition control variable and combustion species re-initialized once every cycle • Ignition model scaling coefficient Cig tuned in the first case, then kept unchanged for the remaining simulations • No tuning of combustion model performed

15. Combustion System Case Study – 2-stroke – Simulation Results: In-cylinder Processes

16. Combustion System Case Study – 2-stroke – Simulation Results: Charge Inhomogeneity • Under 2-stroke operation the in-cylinder charge inhomogeneity can be significant • A quantitative description of inhomogeneity can be provided by using the distribution density function • DDF - a probability density function of the representative variables

17. Combustion System Case Study – 2-stroke – Simulation Results: NOx Emission • NOx prediction based on the extended Zeldovich mechanism, considering thermal NO only • NOx volume fraction monitored at the far end of exhaust port and averaged over a cycle • Correct trend and order of magnitude • A general over-prediction of 30% • Under-prediction in Case A may be attributed to neglecting prompt NOx

18. Combustion System Diesel Engine Application Process • HSDI combustion system development simulation support • 1D performance simulation • Advanced air handling and EGR system development • Advanced aftertreatment modelling • 3D CFD simulation • Fuel – air mixing and combustion for bowl design and swirl development • Combustion prediction for emissions modelling • Intake port development • Steady state air motion development

19. Combustion System Diesel Engine Application Process • Pragmatic approach for rapid application to diesel combustion system simulation • 3D CFD analysis for base system definition • Rapid assessment of critical hardware • Swirl level, chamber design • Specification of initial system for engine demonstration • FIE requirements • Air motion requirements • Full load/part load compromise • Compression ratio selection • Combustion chamber geometry definition • Combustion modelling for emissions prediction • Engine testing for detailed development using DoE based calibration • Tuning of protrusion and nozzle flow • Engine calibration • EGR rate, injection timing, injection specification

20. Diesel Engine Application Process • Combustion system issues for accurate simulation • Geometry definition • Compression ratio volume match • Trapped mass • Imposition of boundary conditions for closed cycle simulation • Multiple full cycle simulations to converge trapped conditions • Coupled 1D/3D in-cylinder for complete engine system modelling • Spray modelling • Fundamental spray match has developed accurate process for modelling • Combustion modelling • Application of RTZF model in VECTIS

21. Combustion System Case Study – Diesel Fuel/Air Mixing for High Performance Methodology – Overall Approach • Geometry assembly • Closed volume at IVC • Mesh generation • Analysis • Fuel/air mixing only • Analysis starts at IVC • Post-processing • Results analysis and engineering review is always critical

22. Combustion System Case Study – Diesel Fuel/Air Mixing for High Performance Methodology - Fuel Spray Modelling • Multi-dimensional modelling of in-cylinder flow and spray • Gas phase • Equations solved in 3-D, Cartesian co-ordinates for conservation of mass, momentum, energy and k- turbulence model • Liquid phase • Discrete droplet model • Lagrangian tracking of droplet parcels and heat and mass transfer through mesh for PDE solution • Sub-models • Huh-Gosman atomisation model • Secondary droplet break-up • Reitz-Diwakar • Liu-Mather-Reitz • Patterson-Reitz • Droplet-turbulence interactions • Droplet-droplet interactions • Validated against diesel spray rig

23. Combustion System Case Study – Diesel Fuel/Air Mixing for High Performance Methodology – Results Analysis • Velocity and fuel vapour field plots require experience and time to interpret • Move towards quantitative representations of data though development of objective measures to quantify changes • Criteria developed and measurable parameters correlated against engine data • Assessment methodology for fuel/air mixing • 2 level zone analysis • Combustion chamber split into distinct zones • Equivalence ratio and fuel vapour distribution within each zone is assessed

24. Combustion System Case Study – Diesel Fuel/Air Mixing for High Performance • Combustion system demonstrator program requiring “right first time” development approach • Program targets • Rated power > 60 kW/l • Peak torque > 200 Nm/l • EURO 4 emissions level • Results shown for initial nozzle specification study comparing 6 hole against 7 hole for the same flow specification

25. 6 hole nozzle shows improved mixing within favourable zone Increased combustible mixture present Combustion System Case Study – Diesel Fuel/Air Mixing for High Performance Methodology – Results Overview

26. 7 hole nozzle shows worse mixture retention - Increased combustible and rich mixture close to bore wall Combustion System Case Study – Diesel Fuel/Air Mixing for High Performance Methodology – Results Overview

27. 7 hole nozzle shows less bowl interaction with reduced mixture in Zone D Combustion System Case Study – Diesel Fuel/Air Mixing for High Performance Methodology – Results Overview

28. 6 hole nozzle shows improved smoke/AFR trade off performance Combustion System Case Study – Diesel Fuel/Air Mixing for High Performance Comparison of Combustion System Performance from Test Data

29. Case Study – Diesel Combustion Modelling Ricardo Two Zone Flamesheet Model Explanation • Overview • Auto-ignition by delay probability integral • Simplified coherent flamesheet model with two-zone gas representation • Emissions chemistry post-processing • Two-zone model • Burnt and unburnt • Each zone has its own enthalpy, fuel mass fraction and air mass fraction • Transport equations solved for • 6 mass fractions, 1 auto-ignition PDF, 4 segregation mass fractions, 2 emissions, 3 enthalpies • 3 temperatures calculated for each cell • Overall, burned and unburned • Fast reactions based on chemical equilibrium calculations • 11 species

30. Case Study – Diesel CFD Combustion Simulation Analysis Process • Two-stage simulation • Compression stroke simulation from IVC to SOI • Swirl imposed as solid body rotation at IVC (based on steady flow rig data) • Trapped mass calculated based on measured fuelling and air/fuel ratio (including EGR) • Solving for momentum, continuity, turbulence and energy • Spray and combustion simulation from SOI to EVO • Spray: Lagrangian discrete droplet method with Patterson-Reitz droplet breakup model • Combustion: RTZF combustion model • NOx: extended Zeldovich NOx model

31. Case Study – Diesel CFD Combustion Simulation Operating Conditions • HSDI engine running at full load • 4000 rev/min full load • Injection timing swing • Combustion modelling prediction • Development of fuel/air mixing analysis process • Animation showing temperature distribution within chamber at rated speed full load

32. Case Study – Diesel CFD Combustion Simulation Combustion Modelling Results • Cylinder pressure trends well produced

33. Case Study – Diesel CFD Combustion Simulation Combustion Modelling Results • NOx emissions trend well reproduced

34. Case Study – Diesel CFD Combustion Simulation Combustion Modelling Summary • Combustion modelling experience shows cylinder pressure generally well reproduced • Over-predicted at earlier timings • Under-predicted at later timings • SOC generally captured well • NOx emissions trend well reproduced • NOx decreases with injection retard • Follows cylinder pressure trend • NOx over-predicted at early timings • NOx under-predicted at later timings • CFD analysis provides valuable information and understanding the HSDI combustion processes to support analytical system development • Routine application to diesel system development including: • Air motion generation and requirements • Combustion chamber geometric configuration • FIE system configuration

35. Agenda • Background • Combustion System Simulation • Intake, Exhaust and Aftertreatment System • Engine Thermal Modelling • Crankcase Breathing • Vehicle Simulation

36. Intake, Exhaust and Aftertreatment Intake System Simulation Applications • Intake system • 1D performance simulation • Intake system design • Boosting system design and development • 3D CFD • Flow performance prediction • AFR distribution prediction • EGR distribution prediction • Flow testing • Manifold flow assessment

37. Intake, Exhaust and Aftertreatment Exhaust System Simulation Applications • Exhaust system • 1D performance simulation • Exhaust system design • Boosting systems • Warm-up modelling • 3D CFD • Flow distribution assessment • Transient performance predictions • Coupled fluid/thermal modelling • Catalyst flow predictions

38. Intake, Exhaust and Aftertreatment Intake and Exhaust System Simulation Methodology • Coupled 1D/3D simulation used extensively as a routine application on exhaust and intake system modelling • Improved modelling for 1-D simulation • Improved boundary conditions for 3-D simulation • Provide a tool to address a wide range of technical problems • Intake system – Air / EGR distribution • Exhaust system – Flow performance / catalyst flow distribution • EGR system – Flow performance / dynamic behaviour • Assess impact of development on engine performance • Integration is characterised by coupling at a time-step level the 1-D gas dynamic code (WAVE) and a 3-D CFD code (VECTIS/STAR-CD)

39. Intake, Exhaust and Aftertreatment Case Study – Exhaust System Simulation Background • Base manifold design support project using CFD and FE analysis to drive manifold design • Vehicle application required use of close coupled catalyst but package constraints were stringent • Focus of fluid simulation • Assess performance benefit of 4-2-1 compared to 4-1 manifold • Assess catalyst flow distribution and recommend design development • Assess sensor location Design 2b Design 1

40. 1-D flow region Intake, Exhaust and Aftertreatment Case Study – Exhaust System Simulation Analysis Process • Engine package models integrated rapidly into CFD tool and mesh generated automatically • Catalyst model used test data to match test rig pressure drop • Coupled 1D/3D analysis undertaken at part load 50 km/hr cruise condition • 1600 rev/min 15 Nm torque • Coupled 1D/3D uses shadow 1-D network for “n” cycles followed by embedded 3-D model with full two-way exchange of boundary conditions at time step level

41. Intake, Exhaust and Aftertreatment Case Study – Exhaust System Simulation Assessment Criteria • Flow distribution assessed in three ways • Maldistribution - SAE 910200 • Uniformity index (g) - SAE 960564 • Cumulative velocity PDF

42. PDF indicates reasonably well distributed flow Uniformity index = 0.93 Velocity PDF indicates better velocity distribution compared to Designs 1 and 2 Uniformity index = 0.99 Intake, Exhaust and Aftertreatment Case Study – Exhaust System Simulation Part Load Simulation Results Design 2b Design 1

43. Intake, Exhaust and Aftertreatment Case Study – Exhaust System Simulation Sensor Location Assessment • Assessment of sensor location based on individual cylinder contribution to flow at specified sensor location • Design 1 shows a good balance of individual cylinders present at baseline sensor position • Design 2 shows a poor balance of individual cylinders present at “design” O2 sensor position • Dominated by CYLINDER 2 Design 1 Design 2b

44. Intake, Exhaust and Aftertreatment Case Study – Exhaust System Simulation Alternative Lambda/O2 Sensors • Design 2 Part Load • Alternative sensor locations assessed rapidly through extraction of revised simulation results for various locations Sensor 1 Sensor 2

45. Intake, Exhaust and Aftertreatment Aftertreatment Simulation - Emissions Control Technology (ECT) Model Range Background • Diesel • Diesel Oxy-Catalyst (DOC) • Diesel Particulate Filter (DPF) • (including CRDPF and CDPF) • Lean NOx Traps (LNT) • Urea Selective Catalyst Reduction (SCR) • Gasoline • Three Way Catalyst (TWC) • Lean NOx Traps (LNT) DPF flow CRDPF

46. DOC DPF SCR DOC DPF SCR Intake, Exhaust and Aftertreatment Aftertreatment Simulation – Methodology ECT System Design Common vectorised approach passes species from unit to unit Exhaust system building from component blocks

47. Thermal sub-model Pressure sub-model Catalysis sub-model Intake, Exhaust and Aftertreatment Methodology – ECT General Model Structure ECT General Model Structure maf T maf P T O2 NO NO2 Pm HC CO SOx CO2 etc. maf P T O2 NO NO2 Pm HC CO SOx CO2 etc. Engine Speed Load emissions MAPS Geometry Material properties

48. Case Study – Aftertreatment Assessment of Exhaust System Layout Background • Project to assess a number of different exhaust configurations in different vehicle packages (Front facing, rear facing, CC CDPF) • Analysis set-up as shown (test data based) • Investigations included assessment of • System specification including insulated pipes • Different catalyst specifications

49. 1.20 g/km 0.24 g/km 0.40 g/km 0.09 g/km Case Study – Aftertreatment Assessment of Exhaust System Layout Example Cycle Emissions Data • Example comparison of cumulative emissions post DOC for under floor against close coupled

50. Case Study – Aftertreatment Assessment of Exhaust System Layout Conversion Matrix for Assessed System Configurations