Powertrain Clean Power Large Eddy Simulations for atomization and spray, Advanced System Engineering N. Lamarque, M. Khan, J. Chesnel*, N. Lu** * Altran Sud ouest ** also CORIA, Rouen www.continental-corporation.com Division Powertrain
Context Automotive trends Diesel Engine LEVII ULEV 10.0 7.5 PM [mg/km] LEVIII 2025 (SULEV30) Gasoline Engine LEVII ULEV 10.0 7.5 PM [mg/km] LEVIII 2025 (SULEV30) 5.0 5.0 CO [g/km] 2.5 NOx [mg/km] CO [g/km] 2.5 NOx [mg/km] 2.5 2.0 1.5 1.0 0.5 50 100 150 200 2.5 2.0 1.5 1.0 0.5 50 100 150 200 US Tier 2 Bin 5 50 Euro 6 Euro 5 US Tier 2 Bin 5 50 Euro 5+6 100 150 Particle number limit for EU 6 2017 : 6 * 10 11 [particles/km] 100 150 200 200 Grams CO 2 per Kilometer no ormalized to NEDC 240 220 200 180 160 140 120 100 250 Total HC / NMOG [mg/km] Solid dots and lines: historical performance Solid dots and dashed lines: enacted targets Solid dots and dotted lines: proposed target US-Car EU Japan China S. Korea India Canada-Car Australia EU 95 gco 2 g/km Phasein 20 2020 2021 0 80 2000 2005 2010 2015 2020 2025 [1] China's target reflects gasoline vehicles only. The target may be lower after new energy vehicles are considered. 140 120 100 80 60 40 WLTP_Ver5.3 FTP cycle US Highway cycle NEDC 250 NMHC /NMOG [mg/km] Normalized cycles 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2 November 13, 2014 Jérémy Chesnel, Continental AG
Context Particle Number emission: where does soot has its origin Refined Simulations tools are required for predictive injection system design Large Eddy Simulations is one of this tool.
Computational Strategy Strategy of weak coupling Simulation N 1 Internal Flow with cavitation and primary Break-Up Ligaments (Output Simulation1) Break-Up analysis module Drops (Inputs Simulation2) Simulation N 2 Spray Larger domain, Larger mesh Drops only 4 November 13, 2014 Jérémy Chesnel, Continental AG
Database from collaborative project (Gasoline Direct Injection) MAGIE XL3.0 test injector Multiple holes «MAGIE» project Funding: FUI (French government) Metering hole External domain Large database on few injectors: Real geometry Real needle lift (X Ray in ANL ) Atomization visualisation Large spray visualisation PDA. 5 November 13, 2014 Continental AG
Database from collaborative project (Gasoline Direct Injection) MAGIE XL3.0 test injector Multiple holes Injection Mach number 0.3-0.8 Spray Plume angle ~15 Re_nozzle, We_nozzle ~2.10 5-8.10 5 Density ratio 609 Typical Stokes number 1 100 needle opening time / Hole flow time 250-500 «MAGIE» project Funding: FUI (French government) Large database on few injectors: Real geometry Real needle lift (X Ray in ANL ) Atomization visualisation Large spray visualisation PDA. 6 November 13, 2014 Continental AG
Computational Strategy OpenSource development platform OpenFOAM Full purpose. Parallel tools. Free Open Source code. Compressible solver Colocated Pressure/velocity 2 nd order Spatial scheme from Demirdzic, I. et al, 1993* First order Euler explicit time scheme Subgrid kinetic energy balance equation Two phase : liquid & vapor ; 1 fluid Interphase dynamic : VOF** Cavitation model: infinitivelly fast or finite rate from N. Lu * Wrongly named PISO in OpenFoam librairies; analogous of SIMPLE for compressible, transonic & barotropic flow. ** Model from Weller, H. & al, based on explicit perfect gaz/barotropic equations Atomization Simulations Special aknowlegement to TGCC, PRACE and GENCI for their support for parrallelisation effort: Speed up Up to 512 processor But limited by case dependency Additional effort under progress November 13, 2014 7 Continental AG
Atomization Simulations Animation @ fuel pressure 90bar 8 November 13, 2014 Continental AG
Atomization Simulations Basic Features: mushroom shape during opening at reduced pressure SAE 2010-01-2247 Diesel hole @reducedp Initial Transient withopenfoam LES-VOF (constant lift artificial) XL3 visualisation, Toulouse Qualitative, semi-artificial but this feature seems well captured 9 November 13, 2014 Continental AG
Atomization Simulations Basic Features: the role of collapse of bubbles in the atomization Collapse plays a role but together with other process: instabilities with high shear, vortex cavitation. See N. Lu et al., ILASS Europe 2012 ; N. Lu, Atomization & Spray 2015 10 November 13, 2014 Continental AG
Atomization Simulations Validation at different Pressures The simulations predicts well: The main liquid core The side jets with small drops The ligaments and drops Sac side 5 bar 90 bar α=21 Seat side CAVITATION α=40 Exp ATOMISATION α=21 α=40 LES 11 November 13, 2014 Continental AG
Atomization Simulations Injection ending simulation Transient flow are important for the real spray quality A simplified testcase of needle closure (injection ending) without needle movement is presented here. 12 November 13, 2014 Continental AG
Atomization Simulations Injection ending simulation Hollow corona shape captured at EOI Too thin film to be captured by the mesh Ligament structure captured with good characteristic size 13 November 13, 2014 Continental AG
Atomization Simulations Injection ending simulation Liquid wetting But the model of static angle has to be reworked Correct Ligament structures 14 November 13, 2014 Continental AG
Simulation coupling Analysis of the atomization results Input : Atomizing flow result 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 Separation Contiuous 0 core. Analysis Process Continous core 2d slice Drop size Probability @100bar x 10-4 2.5 2 1.5 1 0.5 0-0.5-1 40 35 30 25 20 15 Output : Dispersed spray injection conditions Ligament break up model -1.5 10-2 5-2.5 1 1.1 1.2 1.3 1.4 x 10-3 0 15 November 13, 2014 Continental AG
Computational Strategy OpenSource development platform OpenFOAM Full purpose. Parallel tools. Free Open Source code. Compressible solver Colocated Pressure/velocity 2 nd order Spatial scheme from Demirdzic, I. et al, 1993* Euler / Lagrange (no evaporation first) 2 nd order time scheme Dynamic Smagorinski** Eddy lifetime like Subgrid Dispersion model** Subgrid 2 way coupling model** * Wrongly named PISO in OpenFoam librairies; analogous of SIMPLE for compressible, transonic & barotropic flow. ** See Khan, M., PhD thesis, Ecole Centrale de Lyon Spray Simulations 16 November 13, 2014 Continental AG
Spray Simulations Validation on quasi-steady state (long injection) Exp Num 90bar 250 D (5cm distance) Plume center Plume periphery 17 13 November 2014, Continental AG
Spray Simulations Identified zones What we learn first from these high resolution simulations? Where comes the spray angle (& penetration)? Coupled Seconda ary break up < 5-10 D Drag drop <-> gas Instability of the gas shear layer (1rst instability: round vortices) Transition to turbulence 50 to 100-150D Autosimilar powerlaw, gaussian profiles Relaxation to anisotropy ->250D @100bar ->300D @ 200bar 18 November 13, 2014, Continental AG
Spray Simulations Validation on transient Experimental Simulation 10cm Qualitative agreement. The role of the transient effect of needle opening is proven. See Khan, M., PhD thesis, Ecole Centrale de Lyon 19 November 13, 2014 Jérémy Chesnel, Continental AG
Spray Simulations Analysis of transient : Q criterion Spray simulation Qcriterion 10cm The specific dynamic of the spray tip is visible. See Khan, M., PhD thesis, Ecole Centrale de Lyon 20 November 13, 2014 Jérémy Chesnel, Continental AG
Conclusions LES simulation method validated on multi-hole injector XL3.0 vs experimental spray bench images and PDA data, for 100 and 200bar Complementary to industrial fast RANS approach, LES - VOF method seems to be able to capture the primary breakup and support its understanding A complete toolchain has been developed for practical applications using weak coupling LES Lagrangan, despite its intrinsic limits, returns acceptable JPDF using quite simple models Clarification of Drops spray / gaseous jets, an old question, is proposed for the regimes which are studied here. Realistic spray, including transients, can be simulated. Further academic modeling effort on dispersion and 2-way coupling with large interphase velocity is needed. 21 November 13, 2014 Jérémy Chesnel, Continental AG