Nov 13, 2014 - Continental AG. Large database on few injectors: â¢Real geometry. â¢Real needle lift (X Ray in ANL ). â¢Atomization visualisation. â¢Large spray ...
Powertrain – Clean Power Large Eddy Simulations for atomization and spray Dr J. Hélie, Advanced System Engineering N. Lamarque, M. Khan, J. Chesnel*, N. Lu** * Altran Sud ouest www.continental-corporation.com
** also CORIA, Rouen Division Powertrain
Context Automotive trends Diesel Engine
10.0
LEVII ULEV
7.5
PM [mg/km]
Gasoline Engine
LEVIII 2025 (SULEV30)
2.5
2.5 NOx [mg/km]
1.5
1.0
US Tier 2 Bin 5
0.5
50
100
CO [g/km]
200
150
NOx [mg/km] 2.5
2.0
1.5
1.0
0.5
US Tier 2 Bin 5
50 Euro 6
50
Grams CO2 per Kilometer normalized to NEDC
200
Euro 5+6
200
250
Total HC / NMOG [mg/km]
NMHC /NMOG [mg/km]
Normalized cycles
Solid dots and lines: historical performance Solid dots and dashed lines: enacted targets Solid dots and dotted lines: proposed target
US-Car
140
EU
WLTP_Ver5.3 FTP cycle US Highway cycle NEDC
Japan
120
China
200
S. Korea India
180
100
Canada-Car Australia
80
160
60
140
40
120
100
80 2000
EU 95 gCO2 g/km Phasein 2020 – 2021 2005
2010
2015
20
0 2020
[1] China's target reflects gasoline vehicles only. The target may be lower after new energy vehicles are considered.
Dr J. Hélie LES4ICE 2014 2
150
150
200
220
100
100
Particle number limit for EU 6 2017 : 6 * 1011 [particles/km]
150
240
50
Euro 5
100
250
LEVIII 2025 (SULEV30)
5.0
CO [g/km] 2.0
PM [mg/km]
LEVII ULEV 7.5
5.0
2.5
10.0
November 13, 2014 Jérémy Chesnel, © Continental AG
2025
0
200
400
600
800
1000
1200
1400
1600
1800
2000
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. Dr J. Hélie LES4ICE 2014
Computational Strategy Strategy of weak coupling Ligaments (Output Simulation1)
Simulation N°1 Internal Flow with cavitation and primary Break-Up
Simulation N°2 Spray Larger domain, Larger mesh Drops only
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November 13, 2014 Jérémy Chesnel, © Continental AG
Break-Up analysis module Drops (Inputs Simulation2)
Database from collaborative project (Gasoline Direct Injection) MAGIE XL3.0 test injector
Multiple holes
« MAGIE » project Funding: FUI (French government)
Metering hole
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External domain
Large database on few injectors: •Real geometry •Real needle lift (X Ray in ANL ) •Atomization visualisation •Large spray visualisation •PDA….
Database from collaborative project (Gasoline Direct Injection) MAGIE XL3.0 test injector
Multiple holes
Injection Mach number Spray Plume angle Re_nozzle, We_nozzle Density ratio Typical Stokes number needle opening time / Hole flow time
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© Continental AG
0.3-0.8 ~15° ~2.105-8.105 609 1…100 250-500
« 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….
Computational Strategy OpenSource development platform OpenFOAM Full purpose.
Atomization Simulations
Parallel tools. Free Open Source code. Compressible solver Colocated Pressure/velocity 2nd 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
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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
Atomization Simulations Animation @ fuel pressure 90bar
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Atomization Simulations Basic Features: mushroom shape during opening at reduced pressure
SAE 2010- 01-2247 Diesel hole @reducedP XL3 visualisation, Toulouse Initial Transient withOpenFOAM LES-VOF (constant lift – artificial)
Qualitative, semi-artificial but this feature seems well captured Dr J. Hélie LES4ICE 2014 9
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© 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 Dr J. Hélie LES4ICE 2014 10
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© Continental AG
Atomization Simulations Validation at different Pressures 5 bar
The simulations predicts well:
90 bar Seat side
Sac side
α=40°
The main liquid core
Exp α=21°
The side jets with small drops The ligaments and drops
CAVITATION
α α=40° α=21°
ATOMISATION
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LES
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.
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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
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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
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Simulation coupling Analysis of the atomization results Drop size Probability @100bar 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05
Input : Atomizing flow result
Separation
Contiuous core.
Analysis Process
Continous core 2d slice
-4
x 10 2.5
40
2
35
1.5 30 1 0.5
25
0
20
-0.5 15 -1 10
-1.5 -2
5
-2.5 1
1.1
1.2
1.3
0
1.4 -3
x 10
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Output : Dispersed spray injection conditions
Ligament break up model
0
Computational Strategy OpenSource development platform OpenFOAM Full purpose. Parallel tools. Free Open Source code. Compressible solver Colocated Pressure/velocity 2nd order Spatial scheme from Demirdzic, I. et al, 1993* Euler / Lagrange (no evaporation first) 2nd 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
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Spray Simulations
Spray Simulations Validation on quasi-steady state (long injection) Exp
Num
90bar 250 D (5cm distance) Plume center
Plume periphery
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, © Continental AG
What we learn first from these high resolution simulations? ⇒ Where comes the spray angle (& penetration) ?
Coupled Secondary break up
Spray Simulations Identified zones < 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
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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 Dr J. Hélie LES4ICE 2014 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 Dr J. Hélie LES4ICE 2014 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.
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November 13, 2014 Jérémy Chesnel, © Continental AG
