IC Engines Roadmap STAR-CD/es-ice v4.18 and Beyond Richard Johns
Strategy es-ice v4.18 2D Automated Template Meshing Spray-adapted Meshing Physics STAR-CD v4.18 Contents Sprays: ELSA Spray-Wall Impingement Improvements at High Wall Temperatures KHRT Droplet Breakup Model Combustion: ECFM-CLEH, ECFM-LES Fuels: Complex Chemistry using DARS 2-Component Fuel Mixtures and Dual-Fuel operation Real Gas Effects: Compressibility Beyond v4.18 2
Strategy The overall objective is to deliver a holistic capability that fulfils: Ease-of-Use and Process Efficiency through a consistent, processorientated GUI rapid baseline and design iterations Ease-of-Use and Accuracy through meshing technology appropriate to the phenomena being simulated and as automated as possible Accuracy through state-of-the-art models and numerical schemes Generality to simulate combustion systems of the future fuels and operating conditions Speed through high parallel efficiency and appropriate algorithms Support of Research topics and adoption where appropriate 3
es-ice: Automated 2D Template Meshing
Original and New 2D Template Mesh Original Mesh Automatically generated 2D Mesh The new mesh can be generated with a minimum of user input. Only a cell size or number of cell around a valve are currently needed and even this value has a default.
New 2D Mesh showing detail Unstructured mesh allows alignment of mesh with internal model features.
New 2D Mesh Adding mesh optimization puts the mesh where it is needed to get good results. Easy to use since mesh size is based on detail curvature.
Automatic 2D Template Refinement 7613 cells 21270 cells Automatic scaling by 1.7
Automatic 2D Template Refinement Automatic scaling by 1.7
Multihole Nozzles Spray Adapted Meshing
Multihole Nozzles Spray Adapted Meshing
STAR-CD v4.18: ELSA Spray Model ELSA = Eulerian-Lagrangian Spray Atomisation EULERIAN ZONE: multiphase Eulerian modelling of atomisation and dense spray TRANSITION ZONE: switch from Eulerian to Lagrangian calculation as spray dilutes LAGRANGIAN ZONE: classical Lagrangian tracking for droplets in diluted spray zone Mean liquid mass fraction, Y ~ l Liquid surface area density Y i t ~ t U j Y i x j ~ ~ U x j j x j x j t Y i Sc i x j ~ ~ 1 Y l 1 Yl ~ t Source Terms Sc x j l g
STAR-CD v4.18: ELSA Spray Model EVAPORATING SPRAY VALIDATION: Sandia Bomb injection and chamber conditions case number injection pressure chamber temperature chamber density 1 reference 800 800 25 2 3 4 high temperature low injection pressure high injection pressure 800 1100 25 400 800 25 1500 800 25 5 low density 800 800 12
STAR-CD v4.18: ELSA Spray Model EVAPORATING SPRAY VALIDATION liquid and vapour penetration histories Penetrations : Case 1 ==> Case 2 Penetrations : Case 1 ==> Case 4 6.00E-02 6.00E-02 5.00E-02 5.00E-02 4.00E-02 4.00E-02 3.00E-02 2.00E-02 1.00E-02 0.00E+00 0.00E+00 5.00E-04 1.00E-03 Exp. Cas 1 : liquid Exp. Cas 2 : liquid ELSA Cas 1 : liquid ELSA Cas 2 : liquid Exp. Cas 1: vapour Exp. Cas 2: vapour ELSA Cas 1 : vapour ELSA Cas 2 : vapour 3.00E-02 2.00E-02 1.00E-02 0.00E+00 0.00E+00 5.00E-04 1.00E-03 Exp. Cas 1 : liquid Exp. Cas 4 : liquid ELSA Cas 1 : liquid ELSA Cas 4 : liquid Exp. Cas 1: vapour Exp. Cas 4: vapour ELSA Cas 1 : vapour ELSA Cas 4 : vapour time, s time, s T ch liquid penetration vapour penetration 6.00E-02 5.00E-02 Penetrations : Case 1 ==> Case 5 P inj liquid penetration vapour penetration 4.00E-02 3.00E-02 2.00E-02 1.00E-02 0.00E+00 0.00E+00 5.00E-04 1.00E-03 time, s Exp. Cas 1 : liquid Exp. Cas 5 : liquid ELSA Cas 1 : liquid ELSA Cas 5 : liquid Exp. Cas 1: vapour Exp. Cas 5: vapour ELSA Cas 1 : vapour ELSA Cas 5 : vapour ch liquid penetration vapour penetration
STAR-CD v4.18: ELSA Spray Model ELSA model used for Diesel In-cylinder combustion simulation min value 375 K max value (red) 2700 K
Real Gas Effects Peak In-Cylinder pressures have continued to rise: 200 bar in production 250 bar on development dynos Equation of state based on ideal gas law (p = ρrt) become increasingly inaccurate at these high pressures Alternative equations of state have been implemented that allow for the effects of compressibility: Van Der Waals Redlich-Kwong Peng-Robinson Results from all models are very similar
Real Gas Effects: Effect on Pressure
Real Gas Effects: Effect on Temperature
Real Gas Effects: Difference from Ideal Gas
STAR-CD v4.18: ECFM CLEH for Diesel Combustion The ECFM-CLEH model for diesel combustion is released in an improved and updated form ECFM-3Z Zf/um Zf/um ECFM-CLEH Zf/pm Zf/dif Zf/pm Zf/diff Zf/um Transfer is function of c only Transfert if Phi > Phi.crit. The red zone is unmixed burnt gases The transfer between zones is from turbulent mixing and the combustion progresses Z F Z F UM Z F PM Z F DIFF
Calculations using ECFM-CLEH Model Predicted Pcyl and Apparent Rate of Heat Release (AHRR)with change in level of EGR using ECFM-CLEH
Fuel mixtures, dual-fuel operation and complex chemistry STAR-CD v4.18 fully supports both binary mixtures of fuels (eg gasoline + ethanol) and dual fuel engine operation (eg gas engine with diesel pilot) using DARS complex chemistry ECFM-3Z, DARS-TIF combustion models This starts with the fuel evaporation/mixing processes: Fuel/Component 1 Fuel/Component 1 + 2 Fuel/Component 2 And includes the chemical reaction which allows a composition of 100% Fuel 1 to 100% Fuel 2 24
Example: DI Gasoline with E0, E20, E100 25
Fuel Injection and Evaporation Slow evaporation with E100 There is still liquid fuel left at spark timing
Spray and Fuel Mass Fraction Distribution Cylinder centre plane 435 o CA (75 o ATDC) - 5 o After Start of Injection E0 E100 E20 E20 evaporation and mixing modelled as 2-component gasolineethanol mixture 2 scalar fields gasoline and ethanol
Spray and Fuel Mass Fraction Distribution Cylinder centre plane 585 o CA (45 o ABDC) E0 E100 E20
Fuel Mass Fraction Distribution Cylinder centre plane 700 o CA (20 o BTDC) E0 E100 E20
Composition of Active E-20 More Ethanol evaporation at early stage Relative composition progressively approaches proportion of 4.0 This is Total In-Cylinder and hides spatial variations Value < 4 indicate greater proportion of ethanol
E20 Gasoline / Ethanol Ratio Cylinder centre plane 585 o CA 610 o CA 635 o CA Local concentration of gasoline-rich mixture Local Ratio of Gasoline/Ethanol Values > 4 indicate greater proportion of gasoline Values < 4 indicate greater proportion of ethanol
Combustion with ECFM-3Z: Pressure Peak pressure is much lower and also retarded with E100
Combustion with ECFM-3Z: Temperature Lower cylinder temperature with E100 due to high latent heat of Ethanol and later burning
Combustion with ECFM-3Z: Heat Release Rate Slow heat release with E100
Active Fuel Vapour There is substantial unburned ethanol at Exhaust Valve Opening
Example: Dual-Fuel Gas-Diesel Pilot N = 750 rpm Diesel Pilot CA = 716 o (14 o BTDC) c (1 - c) {flame front} Natural Gas Φ = 0.5 Temperature 36
Example: Dual-Fuel Gas-Diesel Pilot Multiple Flame Fronts CA = 740 o (20 o ATDC) c (1 - c) {flame front} Temperature 37
Example: Dual-Fuel Gas-Diesel Pilot Pressure Heat Release Rate
DARS-Fuel: Initially Available Mechanisms Reference to Mechanism Gasoline Toluene Reference Fuel( TRF) consisting of: n-heptane, iso-octane, toluene, mixture according to EU spec Diesel n-decane, a-methylnaphtalene blend (EU diesel blend) Bio-Diesel + Diesel Ethanol + Gasoline DME GTL n-decane, a-methynaphtalene, methyldecanoate as Gasoline (above) + Ethanol n-decane, n-butane, a-methylnaphtalene, cyc-propylhexane, ethanol, DME, methanol, Cyclo-parafine
STAR-CD v4.18: ECFM LES The ECFM-LES model has been developed to address the needs of gasoline engine combustion simulation and is being tested extensively by the University of Modena Aim: Combustion analisys inside an engine cylinder with LES Differences between RANS and LES Comparison with literature 10,000 rpm
c*(1-c) : flame front thickness RANS flame front thickness LES flame front thickness Max pressure in correspondance of flame reaching the wall as observed experimentally Courtesy of the University of Modena
Correspondence c*(1-c) Ʃ LES flame front thickness LES sigma Courtesy of the University of Modena
Flame Front Thickness Front flame thickness from 1.5 to 4.5 mm:
V4.20 and beyond V4.20 & longer term developments User Interface STAR-CCM+ Meshing 3D Template, Auto-meshing Research Sprays VOF/LES Combustion ECFM-LES 44
3D Automatic Template Generation The 2D automation provides quality results for vertical valve engines. Further developments will enable angled valve designs as used in gasoline engines Fit the 3D shape of the features Fit the topology to follow the valve motion in the cylinder head and valve pockets
STAR-CD remains the solver Preprocessing STAR-CCM+ A User Interface based on STAR-CCM+ is being developed.
Automated Meshing: Mesh Structure Constrained Polyhedra Prism Layer Core Cartesian Mesh Re-mesh and map the solution at intervals for complete cycle
Automated Meshing Dynamic Mesh Replacement
Automated Meshing: Solution during Intake Stroke Period: TDC > 30 o ABDC (210 o ) Period: TDC > 30 o ABDC (210 o ) Total of 6 meshes Scalar Flow & Mixing Max cells ~ 1.5M at BDC
Solution Before/After Mesh Replacement Period: TDC > 30 o ABDC (210 o ) Period: TDC > 30 o ABDC (210 o ) Total of 6 meshes Scalar Flow & Mixing Max cells ~ 1.5M at BDC Accurate mapping process for transferring the solution CA = 520 o (20 o BBDC)
Spray Primary Breakup Modelling: ATOMIC
VOF/LES Lagrangian 60 50 40 30 20 10 0 0 200 400 600 800 1000 Experimental Spray_aligned-Reitz KHRT Spray aligned-khrt
VOF/LES Lagrangian Probability Diameter ( m)
LES Application to 4v gasoline engines
LES Application to 4v gasoline engines 55
LES Application to 4v gasoline engines Cylinder Pressure for Individual Cycles Quite good agreement with experimental pressure distribution, especially around the exp. average pressure 56
LES Application to 4v gasoline engines Flame Development for Individual Cycles 57
LES Application to 4v gasoline engines Correlation of Conditions at the Spark Plug with Peak Cylinder Pressure
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