internal flow of automotive injectors: URANS & LES improving the understanding of the atomization. Dr. J. Hélie (Continental Automotive) invited presentation of ...
The role of unsteadiness and coherent structures in the internal flow of automotive injectors: URANS & LES improving the understanding of the atomization Dr. J. Hélie (Continental Automotive) A
invited presentation of LES4ICE conference with contributions of: J. Cousin, A. Berlemont, T. Menard, C. Dumouchel, CORIA, G. Wigley LBoro Univ, A. Heather, OpenCFD, M Gavaises, CUL Univ. O. Soriano, R. Rotondi, J. Shi, H. Nuglisch, B. Imoehl, Continental Automotive
Introduction: Objectives Overview of the atomization process Efficiency Losses
Available energy (∆Pi)
Flowing energy
Cavitation
CASE
Eatom
2 ⋅ σ ⋅ mL 3 2 = ⋅ − ρL D32 d nozzle
© Continental AG
Theoritical Efficiency (%)
MPI 5bar, SMD=50um
0.5%
HPDI 200bar, SMD=11um
0.0657%
DIESEL 2000bar versus 30bar, SMD= 5um
0.0015 %
Still a lot to do ! JH / Oct. 2010
Secondary flow
Turbulence
Introduction: Objectives Injection Trends for 2015-2020 (for Diesel & Gasoline)
Increase the Pressure
Increase the Temperature
Increase the fuel diversity
+ tendency of Diesel & last year
+ overheated conditions
+ less dependency/ petroleum
- request more and more pressure
- difficulty of heated tip
- system quality
- energy spent Increase the Nozzle complexity
Increase the Holes number
Increase the needle dynamic
+ better atomisation
(Decrease the hole diameter)
+ multi injection
- tolerances
better(Diesel) or worst (Gasoline) atomisation
- actuator (Piezo faster)
- coking - jet-to-jet interaction (Group-hole)
JH / Oct. 2010
© Continental AG
Great challenges ! R. Rotonti, O. Soriano, J. Hélie, SIA 2010
- constraint on cost
Introduction: Objectives Overview of the Design Process for industrial application performances
Design variation CFD investigate (RANS)
Design rules Turbulence intensity Cavitation intensity
Prototypes
rules
Referent Design CFD investigate (detailed URANS, LES)
Disavantage: long CPU time JH / Oct. 2010
© Continental AG
Atomization factors
methodology
Introduction: Context Overview of current injectors designs in the litterature Valve Covered ( Diesel): lift (levée)
needle (aiguille)
seat (siege, fermeture)
sac volume Micro Sac, (Diesel & Gasoline type) : Simplified : academic world (Hiroyasu et al. ..)
divergent
Flat Sac, (Gasoline type) :
step
JH / Oct. 2010
© Continental AG
Introduction: Why LES for Atomization ? How it proceeds in automotive atomizer ? Let's consider a liquid sheet that is expanding (through tangential velocity, swirl, turbulence...)
Regime of inertial Force
mass balance :
r ∫V S1
r2 kinetic energy balance ( V ∫
) – Surface tension force
S1
cannot be conserved both without dissipation !
JH / Oct. 2010
© Continental AG
Introduction : Why LES for Atomization ? 2D numerical Experiment 1/3 Geometrical parameters
MODEL VORTEX X
l d
Y
GAS
LIQUID
l d L X = 60l Y = 30l
Physical parameters
ρ G , µG ρ L , µ L σ u θ max
Temporal evolution of the Interface and Vorticity field
JH / Oct. 2010
© Continental AG
J. Cousin, T. Menard, A. Berlemont, J. Hélie, ILASS 2010
Non Dimensional parameters (PI theorem)
d /l
ρ G/ ρ L µ G/ µL Re = ρ L uθ max l / µ L We = ρ L u 2θ max l / σ
Introduction : Why LES for Atomization ? 2D numerical Experiment 2/3 Re Re (-) (-) Re (-) (-)
10000 10000 10000 10000
Re varies We varies R = 1.126 10-3 M = 1.566 10-2 d = 2l L=15l l=0.001 m
Detachment Detachment Detachment Detachment
1000 1000 1000 1000
No detachment No detachment No detachment 100 100 100 11 100 1 1
10 10 10 10 (-) We
A minimum energy is required to eject a drop Simple model from Energy & Mass conservation + Rayleigh Breakup
JH / Oct. 2010
© Continental AG
ρ LU 2l We = = 7.56 σ
We (-) (-) We (-)
100 100 100 100
Existence of a single curve that separates the two behaviors
J. Cousin, T. Menard, A. Berlemont, J. Hélie, ILASS 2010
Introduction : Why LES for Atomization ? 2D numerical Experiment 2/3 Re (-) 10000
Re varies We varies R = 1.126 10-3 M = 1.566 10-2 d = 2l L=15l l=0.001 m
1000
100 1.E-04
1.E-03
1.E-02
1.E-01
Oh (-)
Ohnesorge-Reynolds diagram
JH / Oct. 2010
© Continental AG
We Oh = = Re
J. Cousin, T. Menard, A. Berlemont, J. Hélie, ILASS 2010
µL ρ Lσl
Low Pressure Atomizer (MPI, SCR, DDS) Low Weber & Reynolds Number •Low Pressure Atomizer •Long Opening time
MPI (Deka VII)
•Holes direction for MPI targetting •Dosing & atomization for DDS & SCR
DDS injector
•Various Fluids used •Cost limited
SCR injector
JH / Oct. 2010
© Continental AG
Low Pressure Atomizer (MPI, SCR, DDS) Triple Disk Experiment The atomization energy balance was established Swirl velocity at the nozzle exit Turbulence intensity at the nozzle exit
x z
vs Surface creation σ/D32 (kg/ms ) 2
700
1000
σ/D32 (kg/ms2) Water Linear regression CSL2 (model k-ε) CSL2 (model RSM)
600 800
500 400
600
300 400
200 200
100 0
σ = 9.63 x10 − 3 (Ek + ρL Tke ) + 170 D32
0
0
10000
20000
30000
Ek + ρLTke (kg/ms ) 2
40000
50000
0
10000
20000
30000
40000
50000
60000
70000
Ek + ρLTke (kg/ms ) 2
Formalism of the maximum entropy principle and the interface density balance were used to establish a theoretical modeling of the break up process JH / Oct. 2010
C. Dumouchel & J. Cousin CORIA group published in Experiments in Fluids 2005 Int. J. of Multiphase Flow 2007, J. of flow visualization & image processing 2008...
© Continental AG
y
Low Pressure Atomizer (MPI, SCR) Triple Disk Experiment : RANS Approach Variant090
Variant000
m²/s²
Variant200
Variant500
Variant700
Variant900
Ek
0.006
0.006
0.006
0.006
0.004
0.004 0.002
0.000 0
100
200 300 D (µm)
400
0.000 0 500
0.004 0.002
100
200 300 D (µm)
400
0.000 500 0
0.008 075076700
0.004 0.002
100
200 300 D (µm)
400
0.000 500 0
0.004 0.002
100
Volume based drop size distribution
200 300 D (µm)
C. Dumouchel & J. Cousin CORIA group published in Experiments in Fluids 2005 Int. J. of Multiphase Flow 2007, J. of flow visualization & image processing 2008...
© Continental AG
075076900
0.006 fv (µm-1)
075076500 0.008
fv (µm-1)
075076200 0.008
fv (µm-1)
0750760900.008
0.002
S1I1 WATER ∆Pi = 3 bar
JH / Oct. 2010
0.008
fv (µm-1)
fv (µm-1)
Tke
400
0.000 5000
100
200 300 D (µm)
400
500
Low Pressure Atomizer (MPI, SCR) Triple Disk Experiment : RANS Approach coupled with Interface Solver: ARCHER (CORIA) Level Set+VOF+Ghost Fluid + Input statistical at intlet
Solver: Fluent6.2 RNG k-eps simulation
removed turbulence (a)
non axial velocity
rebuilt turbulence
(b)
turbulent kinetic energy
Acceptable morphology of the liquid system was found BUT Overestimated jet angle at the vicinity of the nozzle exit ⇒more accurate internal flow simulation is necessary to provide better quantitative results. JH / Oct. 2010
© Continental AG
A. Berlemont, J. Cousin, S. Grout, T. Menard, ASME 2010
Low Pressure Atomizer (MPI, SCR) Triple Disk Experiment : LES Approach of Internal Flow
Solver: Fluent6.2 LES, cst smago
Computational mesh
Fluid trajectories
Experimental validation based on hot wire measurements applied on a large gas scale model 2 -2
Tke(m s ) 16
Turbulent kinetic energy profile along the x and Tke(mys )directions 2 -2
25
(b)
(a)
14
20
12 10 8
15
LES EXP
LES
10
6
EXP
4 5
2 0 0.E+00
2.E-05
4.E-05
x (m)
6.E-05
8.E-05
0 0.0E+00
4.0E-05
8.0E-05
y (m)
A. Berlemont, J. Cousin, S. Grout, T. Menard, ASME 2010 JH / Oct. 2010
© Continental AG
1.2E-04
1.6E-04
Low Pressure Atomizer (MPI, SCR) Triple Disk Experiment : LES Approach Coupled to Interface
Solver: ARCHER (CORIA) Level Set+VOF+Ghost Fluid + LES results at intlet
The calculated jet angle (26°) is fairly close to the measured one (24°). LES simulations provide much better initial conditions for the jet simulation compared to what was previously with RANS
Jet angle
JH / Oct. 2010
© Continental AG
One of the main visible difference on these two images is the number of droplets in the visualized domain. When the simulation starts, the velocity of the discharged jet is high and a large number of droplets are created in the jet leading edge. This is not the case for the real application; when the injection starts, the jet velocity continuously increases and the production of droplets is limited ⇒ Spurious difference which can be easily corrected
A. Berlemont, J. Cousin, S. Grout, T. Menard, ASME 2010
Low Pressure Atomizer (MPI, SCR) Triple Disk Experiment : LES Approach coupled to Interface
Solver: ARCHER (CORIA) Level Set+VOF+Ghost Fluid + LES results at intlet
During steady state operation, the simulation reports well the particular breakup mechanism. 1. The liquid jet flattening in the vicinity of the discharge orifice is well reproduced. Rims formation (left: visualization, right: simulation)
2. The reorganization into a ligament network is also observed. 3. This leads to the formation of two external rims. Perforations occur in the jet center.
Perforation process left: visualization, right: simulation
The numerical simulation predicts perforations closer to the orifice It is due to the jet flattening, the liquid sheet becomes too thin to be predicted with a sufficient accuracy with respect to the computational cell size set to 5 µm. ⇒ AMR requested for fully predictive VOF
JH / Oct. 2010
© Continental AG
A. Berlemont, J. Cousin, S. Grout, T. Menard, ASME 2010
High Weber & Reynolds Number – example of Diesel Injectors
switch leakage reduction 2000 bar capability Smart Electronic control algorithms ... Nozzle improved
PCR Servo Valve Euro 6
(…)
Development targets: -
Injector Closed Loop Control
-
Hydraulic-free: Full rate shaping possible
(...) PCR NG – direct drive
JH / Oct. 2010
© Continental AG
L. Passilly, F. Atzler, K. Wenzlawski, SIA 2010
High Weber & Reynolds Number – Diesel Injectors Cavitation for industrial application: Shear cavitation, RANS & LES Academic investigation, including both real-size and largescale, sac-type and VCO-type Diesel nozzles, with either cylindrical or tapered holes, inlet sharp or rounded, as here from City University London
Solver: Homecode City University london Model: URANS + lagrangian cavitation model*
Mean LES
RANS Instantaneous LES Similar result for the structure of RANS with the LES mean pressure field. However the instantaneous solution provides a more detailed representation of the turbulent structures © Continental AG A Theodorakakos, E Giannadakis, D. Papoulias, M Gavaises, SAE 2009-01-0833 A Papoutsakis,
JH / Oct. 2010
High Weber & Reynolds Number – Diesel Injectors Cavitation for industrial application: cavitation vortex, also named cavitation string Cavitation strings are forming at areas where large-scale vortical structures develop Such large-scale vortical structures although they are evident in CFD simulations, are rather transient and strongly affected by the nozzle geometry, operating conditions, needle motion, etc.
0
Vortex core between adjacent holes
JH / Oct. 2010
Swirl (-)
0.5
Sharp flow turn inside the sac volume & separarions points
Vortex core inside the injection hole
© Continental AG
A Papoutsakis, A Theodorakakos, E Giannadakis, D. Papoulias, M Gavaises, SAE 2009-01-0833
Solver: Homecode City University london Model: URANS + lagrangian cavitation model*
High Weber & Reynolds Number – Diesel Injectors Cavitation for industrial application: modeling the effect on atomization Cavitation affects the atomization, flow direction & the flow profile Two Zones model.
Solver: CFX R-P cavitation model CONTI Improved Baumgarten Model*
(Baumgarten,C. – U. Hannover 2003)
Vapour Zone (Zone 2)
Liquid Zone (Zone 1)
New droplets 2 Phase-cavitating turbulent nozzle flow
Injected ligament
Collapsing ligament
Φ 2/2 Φ1
Rayleigh´s tcoll
Acting break-up mechanisms: Cavitation Turbulence Nozzle flow
Primary break-up Diesel – Euler approach Diesel Vapour – Euler approach
JH / Oct. 2010
© Continental AG
O. Soriano et al., ILASS Europe 2008
Acting break-up mechanisms: Fuel - ambient gas interaction Secondary break-up
Diesel – Lagrange approach Gas – Euler approach
Medium Weber & Reynolds Number – Pintle Gasoline Injectors Technical Data Working Flow Range: Static flow:
Thermal Compensator
> 50
and inlet tubes
> 35 g/s
Minimum dynamic flow. < 2 mg/str Spray angle:
60 deg to 120°
SMD size:
~ 10 - 15 µm
Opening/Closing time:
≥ 150 µs
Temperature range:
-30...+140°C
System Pressure:
5...20 MPa
Piezo Electrical Activator
-Outward opening -fine liquid corrona cartridge -geometrical angle
seat needle
JH / Oct. 2010
© Continental AG
Medium Weber & Reynolds Number – Pintle Gasoline Injectors Specific Atomization Process
Piezo produces a new (non linear) mode of atomization: Hollow cone with steaks (micro-jets)
Delta P = 5 bar
JH / Oct. 2010
Delta P = 200 bar
G Delay, B. Prosperi, R. Bazile, H Nuglisch, J. Hélie , Experiments in Fluids, 2007 & Work of J. Cousin, CORIA & G. Wigley, Louborough Univ
© Continental AG
Medium Weber & Reynolds Number – Pintle Gasoline Injectors Specific Atomization Process
Recirculations in the needle sac
Solver: Homecode City University london Model: URANS + lagrangian cavitation model*
Injector
Main flow jet Counter-rotating recirculation zones formed inside the dead volume below the lower needle guide
E Giannadakis, D Papoulias, A Theodorakakos, M Gavaises, Proc. IMechE Vol. 222 Part D: J. Automobile Engineering © Continental AG Gavaises, M., Tonini, S., Marchi, A., Theodorakakos,A., Bouris, D., and Matteucci, L., Int. J.Engine Res., 2006, 7, 381–397.
JH / Oct. 2010
Medium Weber & Reynolds Number – Pintle Gasoline Specific Flow - Atomization Process : results of large scale nozzle Injector
Solver: Homecode City University london Injectors Model: URANS + lagrangian cavitation model*
High Speed Imaging: Flow images reveal cavitation formation in
a rather unstable pattern consisting of vapour ‘pockets’
Cavitation
Simulation: Sample vapour bubbles and vapour volume fraction: A similar pattern is predicted by the simulation model
0% vapour 40% Visualisation . window E Giannadakis, D Papoulias, A Theodorakakos, M Gavaises, Proc. IMechE Vol. 222 Part D: J. Automobile Engineering © Continental AG JH / Oct. 2010
Gavaises, M., Tonini, S., Marchi, A., Theodorakakos,A., Bouris, D., and Matteucci, L., Int. J.Engine Res., 2006, 7, 381–397.
Medium Weber & Reynolds Number – Pintle Gasoline Injectors LES + VOF: Internal Flow Results: real injector geometry Solver: OpenFOAM Model: LES (smago) + VOF*
injection of turbulence at intlet
10 angular degrees domain
JH / Oct. 2010
© Continental AG
Results Continental Automotive/OpenCFD, PREDIT IDE2 PROJECT
Medium Weber & Reynolds Number – Pintle Gasoline Injectors LES + VOF: External Flow Result : real injector geometry nozzle exit
Liquid/Gas interface colored by the air velocity
Streaky structures
JH / Oct. 2010
Results Continental Automotive/OpenCFD, PREDIT IDE2 PROJECT Picture CORIA, PREDIT IDE2 PROJECT
© Continental AG
Solver: OpenFOAM Model: LES (smago) + VOF*
Medium Weber & Reynolds Number – Low L/D MultiHole Gasoline Injectors Present generation of Multihole gasoline injectors DI gasoline homogeneous combustion Oriented downsized engine 200bar sample operational fuel pressure fast magnetic actuation Studied injectors, special prototype: 3 holes 90deg wide spray angle XL2 5.5g/s N-Heptane @ 100bar No Step-Hole
seat sac
6 holes = L/D = 1 to 1.2 hole
JH / Oct. 2010
© Continental AG
Solver: CFX Model:U-RANS SST LES SAS
Medium Weber & Reynolds Number – Low L/D Numerical Study, validation at low pressure without cavitation Mesh:
SST_basic
SAS_fine
Q8.1E+11
1.66 M Cells up to 3.2M
Q2.5E+12
"URANS" solution
0.01 0.009 0.008 0.007 0.006 0.005 0.004
Mass flow at outlet
0.003 0.002 0.001 0 0
Power Spectrum
Experimental evidence: -non unique frequency, -one important frequency identified around 25kHz
0.5
x
1
1.5
2
2.5
3
3.5
4
4.5
5 4
x
10
x
10
x
10
x
10
x
10
x
10
7
10
16
14
12
10
8
6
4
Pressure
2
0 0
0.5
x
1
1.5
2
2.5
3
3.5
4
4.5
5 4
11
10
7
6
5
4
3
Total pressure
2
1
0 0
0.5
x
1
1.5
2
2.5
3
3.5
4
4.5
5 4
15
10
2.5
2
1.5
1
0.5
0 0
12
0.5
x
1
1.5
2
2.5
3
3.5
4
4.5
Velocity U
5 4
14
10
10
8
6
4
2
0 0
2.2
0.5
x
1
1.5
2
2.5
3
3.5
4
4.5
Velocity V
5 4
14
10
2 1.8 1.6 1.4 1.2 1 0.8 0.6
Velocity W
0.4 0.2 0 0
0.5
1
x
1.5
2
2.5
20
10
0
3
3.5
4
4.5
5 4
40
30
50
"LES" solution
−3
10
4
3.5
3
2.5
2
1.5
1
0.5
0 0
x
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5 4
x
10
x
10
x
10
x
10
9
10
6
Mass flow at outlet
Power Spectrum
5
4
3
2
1
0 0
6
x
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5 4
9
10
5
Pressure
4
3
2
1
0 0
x
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5 4
13
10
3.5
3
Total pressure
2.5
2
1.5
1
0.5
0 0
x
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5 4
13
10
Velocity U
10
9
8
7
6
5
4
3
2
1
0 0
x
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5 4
x
10
x
10
13
10
2.5
Velocity V
2
1.5
1
0.5
0 0
JH / Oct. 2010
© Continental AG
0
0.5
1
1.5
2
2.5
3
3.5
Frequency [k Hz]
J Shi, K. Wenzlawski, J. Helie, H. Nuglisch, J. Cousin, ILASS 2010
4
4.5
5 4
Velocity W
50
Medium Weber & Reynolds Number – Low L/D MultiHole Gasoline Injectors Internal Flow: Fluid Properties, cavitation Simplified 2D Nozzle flow AVL testcase exhibits the main features.
Solver: CFX Model:RANS + R-P cavitation
"shear cavitation"
Cavitation dominated by the shear :
Experimental data available for diesel
low effect of sat. vapour pressure
100bar versus 33 bar, Geometry J
large effect of viscosity
Diesel, 20 °C
JH / Oct. 2010
© Continental AG
n-Heptane, 20 °C
J.Shi & M. Arafin, ILASS 2010
n-Heptane, 70 °C
Medium Weber & Reynolds Number – Low L/D Unsteadiness of the flow Coherent structures at various pressure, developing from the nozzle :
5 bar
10 bar
50 bar
Unsteadiness during injection (various times shown, @50bar):
JH / Oct. 2010
© Continental AG
Results CORIA, FUI "MAGIE" Project
120 bar
CONCLUSIONS Great Challenges in CFD to support design of next generation of automotive injectors Most of the time, URANS returns correct trends for a fast answer LES is requested as input of external VOF Cavitation model is a limiting factor for accuracy–no consensus in the community.
Cases of Low Pressure, High Pressure Diesel, Medium Pressure nozzle with Pintle needle and Short L/D have been presented Internal Flow & Atomization are highly coupled Coherence of the internal flow has to be captured for the simulation of the breakup Validation: Qualitative results satisfying, quantitative results request continuous efforts &industry-academy collaborations
JH / Oct. 2010
© Continental AG
Thank you for your Attention
Questions ? JH / Oct. 2010
© Continental AG
