Lib-ICE A C++ object-oriented library for internal combustion engine simulations: spray and combustion modeling

5 th OpenFOAM Workshop, Goteborg, 21-24 June 2010 Lib-ICE A C++ object-oriented library for internal combustion engine simulations: spray and combustion modeling T. Lucchini, G. D Errico, D. Ettorre, E. Spagnoli, G. Ferrari Internal Combustion Engine Group, Department of Energy Politecnico di Milano

Topics Development and application of numerical models (Lib-ICE) to simulate in-cylinder flows and combustion in IC engines using the OpenFOAM technology: Spray modeling Liquid film formation modeling Mesh management Diesel combustion SI-combustion Application to real engine cases, validation with experimental data.

Lib-ICE Code structure applications Diesel SI-Combustion Cold-flow Lib-ICE_1.5-dev OpenFOAM-dev Features of OpenFOAM+advaced models contributed by different research groups src utilities dieselspraypolimi thermophysicalmodelspolimi chemistrymodelpolimi wallfilmpolimi ldusolverspolimi

Mesh management Mesh management Automatic mesh motion, topological changes and adaptive local mesh refinement used in combination to ensure high grid quality and a reduced number of meshes to cover the simulation of the whole cycle. Work developed in collaboration with prof. H. Jasak and Dr. Zeljko Tukovic (University of Zagreb)

Lib-ICE spray models Review of the implemented capabilities Injection Atomization Breakup Evaporation Heat-transfer Wall impingement Collision Blob, Huh, Hollow-cone, Pressure-swirl Huh-Gosman, Bianchi, WAVE, LISA TAB, ETAB, KH-RT, Reitz-Diwakar Frossling Ranz-Marschall Naber-Reitz, Bai-Gosman, remove, rebound O Rourke, Nordin

Spray models: new capabilities Blob injection: droplets are injected with the same nozzle diameter and injection velocity. Turbulent quantities (L t, τ t ) initialized for each droplet according to the nozzle flow conditions. Liquid jet atomization is modeled as: 1) Diameter reduction of the injected droplets 2) Stripping of secondary droplets from the liquid jet Model developed in collaboration with Prof. G. M Bianchi and Dr. F. Brusiani (DIEM - University of Bologna).

Spray models: new capabilities Diameter reduction of the injected parcels: dd dt = C 5 L a τ a Secondary droplet diameter at breakup-time: d stable = C w d prob R Multiphase LES calculations performed for different Reynolds nozzle number to: Identify suitable relations for L a and τ a Define the main model tuning constants (C w, C 5 ). Calculate the secondary droplet size at breakup time (d prob ) Sect. A Sect. B Sect. C

Spray models: new capabilities Model validation at constant-volume conditions 7-hole injector, opening angle: 148º. Nozzle diameter: 0.141 mm Pilot+main injections considered for each operating point. Injected mass flow measured through the AVL flow rate meter. S1 S2 S3 S3 Strategy 1500 x 2 2000 x 5 2000 full 2500 x 8 Q pilot [mm 3 ] 1.04 0.93 0.93 1.04 Q tot [mm 3 ] 10.94 20.01 73.19 29.67 ρ AMB [kg/m 3 ] 16.3 18.6 33.6 23.9 fuel inj. rate [mg/µs] 0.5 0.4 0.3 0.2 0.1 0.0 1500 x 2 2000 x 5 2500 x 8 2000 full Experimental data from Dr. Montanaro and Dr. Allocca (CNR-Istituto Motori, Naples) 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 time [µs]

Spray models: new capabilities Application of Adaptive Local Mesh Refinement (ALMR) to a non-evaporating diesel spray case. 3 ms ASOI 6 ms ASOI Spray evolution correctly described in terms of: Primary and secondary breakup. Cone angle. Consistency and convergence of ALMR verified in previous works. 9 ms ASOI 12 ms ASOI

Spray models: new capabilities S1 S2 S3 S4

Wall film model: update Model implementation now completed. Solution of the liquid film governing equations: Mass Momentum Energy Improved calculation of the droplet impact pressure. Now the Bai-Gosman wall-impingement model is available. Support for parallelization and topological changes. Future developments: new impingement model to account for higher Weber impact numbers. Droplet formation model from sharp corners.

Wall film model: update Example of application: iso-octane droplets splashing on to a hot surface (400 K) Spray and liquid film temperature evolution. Fuel evaporation from liquid film. Work carried out in collaboration with Dr. Z. Tukovic and Prof. H. Jasak (FSB - University of Zagreb)

Lib-ICE: Diesel combustion Objective: Improve the existing combustion models to provide advanced diagnostic and development tools to design and simulate Diesel engines. Current models: TITC CTC PSR Tabulation of ignition delays + Eddy Dissipation model (4 species: fuel, air, products, egr) Shell Model + Characteristic Time-scale Combustion model (11 species, chemical equilibrium) Detailed chemistry + ISAT + DAC (TDAC)

Diesel combustion CTC (Characteristic Time-scale Combustion Model) 11 chemical species (fuel, O 2, N 2, CO, CO 2, H 2 O, O, OH, NO, H, H 2 ) Auto-ignition computed by the Shell auto-ignition model (available set of constants for different fuels). Turbulent combustion simulated accounting for both laminar and turbulent time scales: Y i, TC = Y i Y τ C * i, where τ = τ + C l fτ t Incorporation of Zeldovich mechanism and Hiroyasu models to predict NO x and soot emissions. HC estimated as unburned fuel.

Diesel combustion: CTC model Experimental validation Common Rail Diesel Engine Work carried out in collaboration with Ing. Rita Di Gioia, Ing. Davide Carpentiero, Ing. Samuele Bertacchini (Magneti- Marelli Powertrain, Bologna). Spray-oriented grid to better predict the fuel-air mixing process Initial conditions at IVC (pressure, temperature) taken from 1D simulations of the whole engine system, including turbocharger and EGR Initial flow field: wheel-flow profile according to the experimental swirl ratio (2.2)

Diesel combustion: CTC model Experimental validation Common Rail Diesel Engine 1500 rpm, BMEP = 2 bar 100% 0% EGR Qpil Qpre Qmain Low load with high EGR rate and three injections

Diesel combustion: CTC model Experimental validation Common Rail Diesel Engine 1500 rpm, BMEP = 6 bar 100% 0% EGR Qpil Qpre Qmain Medium load with high EGR rate and three injections

Diesel combustion: CTC model Experimental validation Common Rail Diesel Engine 1500 rpm, BMEP = 12 bar 100% 0% EGR Qpil Qpre Qmain High load without EGR and three injections

Diesel combustion: CTC model Experimental validation Common Rail Diesel Engine 4000 rpm, BMEP = 16 bar 100% 0% EGR Qpil Qpre Qmain Full load without EGR and a single injection

Diesel combustion: CTC model Experimental validation Common Rail Diesel Engine Pollutant emissions NO x 1500 rpm NO x emissions NO x [ppm] Exp. Calc. BMEP [bar]

Diesel combustion: CTC model Experimental validation Common Rail Diesel Engine Pollutant emissions soot 1500 rpm soot emissions soot [ppm] Exp. Calc. BMEP [bar]

Diesel combustion - detailed chemistry (PSR) Detailed chemistry is necessary to describe the main features of the Diesel spray flame, both under conventional and new combustion modes: Auto-ignition Pollutant formation (soot, NO x ) Diffusion flame Proposed approach: perfectly stirred reactor (PSR) model based on direct integration of the chemical mechanism in each cell. ISAT+DAC (TDAC) technique applied to reduce the computational time. Work carried out in collaboration with Phd student Francesco Contino (University of Leouvain, Belgium). q ψ retrieve q ( ) l R ψ ISAT q ψ add grow q q R( ψ ) ( ) R ψ a DAC q ψ a ODE solver Speed-up factor: 4 300 due to a reduction of ODE integrations.

Diesel combustion: PSR+TDAC Sandia optical engine: fuel-air mixing and combustion Calculations performed both at non-reacting and reacting conditions using a PRF29 fuel. Reduced chemical mechanism applied (49 species, 122 reactions). Two piston bowl configurations evaluated with different diameters and depths. Operating condition: partial load with 60% equivalent EGR. Compression simulated with a layered/coarse mesh, ALMR applied during fuel/air mixing and combustion. 70% bowl 80% bowl

Diesel combustion: PSR+TDAC Sandia optical engine: fuel-air mixing and flame propagation using ALMR and TDAC 4 CA 7 CA 14 CA 19 CA The grid is dynamically refined where the spray evolves and air-fuel mixing takes place. ALMR combined with TDAC: significant reduction of CPU time, but the accuracy is completely preserved.

Diesel combustion: PSR+TDAC 70% bowl, 8º ATDC 80% bowl, 9º ATDC 7 mm, exp 12 mm, exp 18 mm, exp 7 mm, exp 10 mm, exp 14 mm, exp 7 mm, calc 12 mm, calc 18 mm, calc 7 mm, calc 10 mm, calc 14 mm, calc Spray model validation: comparison with optical measurements of equivalence ratio distribution. Combustion model validation with in-cylinder pressure and heat release rate profiles.

Lib-ICE: SI-combustion ECFM-3z model now available in Lib-ICE. Possibility to simulate combustion in direct-injection, SI-engines accounting for: Ignition, modeled using the Eulerian AKTIM approach Turbulent combustion, using a 2- equation model transporting the flame surface density Σ flame propagation A u A b M u M b ρσ t + ρuiσ + x i = x ( P1 + P2 + P3 ) Σ D + Pk i µ Sc + µ t Sc t Σ x i F u unburned gases F b burned gases Mixing controlled combustion Burned gas composition computed at equilibrium. Possibility to predict soot, NO x and knock (Shell model).

SI-combustion Example of applications: flame kernel growth in an optical engine with central and peripheral ignition. Central ignition Peripheral ignition

Conclusions Lib-ICE combined with OpenFOAM-dev to simulate real IC engines: Gas exchange Fuel-air mixing including wall-film formation and evolution, Combustion (Diesel, SI, GDI, PCCI, HCCI) Future works: Identification of a suitable turbulence-chemistry interaction model for non-premixed combustion simulations with detailed chemistry. Including re-meshing techniques into the mesh-motion algorithms to further reduce the number of meshes and improve their quality. Introduction of detailed soot models for both Diesel and GDI combustion.