1. ECN 4 Topic 8: Internal & Near Nozzle Flow Modeling Spray G Organizer: Chris Powell Argonne National Laboratory Ronald Grover, Presenter General Motors R&D
General introduction
Talk dovetails to Dan Duke’s presentation

2. Presentation Contents
Modelling Approaches
Simulation Techniques
Boundary Conditions
Meshing
ECN 4 Simulation Results
Injector coefficients
Representative contour plots
Next Steps for Spray G
Encouraging more contributors!

3. Contributors Acknowledgement
Three institutions contributed simulation results
University of Massachusetts-Amherst and General Motors
Maryam Moulai, David Schmidt (UMass)/Ronald Grover (GM)
* Results published in SAE
Delphi
Bizhan Befrui, Andreas Aye, Adrien Bossi
* Representative modelling approach outlined in SAE
Argonne National Laboratory
Kaushik Saha, Sibendu Som, Michele Battistoni
*Results will be available in ASME paper ICEF in Nov, 2015
Politecnico di Milano
Ehsanallah Tahmasebi , Tommaso Lucchini, Gianluca D’Errico
*Details about the solver and its validity presented by (Salvador et al 2010)
Acknowledgement
GridPro
Thank the contributors and acknowledge GridPro

4. Spray G Nominal Baseline Data/Conditions
Fuel
Isooctane
Injection Pressure
20 MPa
Fuel Temperature
90° C ( K)
Ambient Temperature
300° C ( K)
Ambient Density
3.5 kg/m3
- Ambient Pressure
5.97 bar (N2); 5.77 bar (Air)
Injected Quantity
10 mg
Injection Duration
780 µs (“actual”)
Number of Nozzle Holes 8
Hole Diameter
165 µm
Fully Included Angle
80°
NOTES:
Delphi simulation was conducted at injection pressure = 10MPa, atmospheric conditions (Spray G condition forthcoming)
Results for the Spray G2 condition are also available but will be presented at a later time (teaser shown at the end of the presentation)

5. Modelling Approaches

6. Internal Modeling Codes
Institution
UMass/GM
ANL
Delphi
PoliMi
Code
HRMFoam
CONVERGE
OpenFOAM
Origin
UMass
Convergent Science
OpenCFD
OpenCFD (?)
External Coupling NO
Made best guess on PoliMi contribution
UMass pulls base source from the extend branch of OpenFOAM
External coupling = used these data to initialize an external spray solver

7. Approaches Institution/Code UMass/GM ANL Delphi PoliMi Liquid fuel
Iso-Octane
N-Heptane
Equation of State
Compressible
Incompressible
Compressible?
Cavitation Enabled?
Yes No
Cavitation Model
Homogenous Relaxation
Homogeneous Relaxation -
cavitatingFoam multiphase solver
Inclusion of turbulent viscous energy generation?
No?
Turbulence
RANS
k-epsilon
K-epsilon
VOF-LES, SGS Smagorinsky-Lilly EVM, k-Eq.
k-Omega SST
Spatial Discretization
2nd order
Fuel Properties
REFPROP
(input table)
CONVERGE, Dymond et al. 1985
Reference
(from REFPROP)
Ambient Properties
Ideal Gas
Ideal gas
Submerged ?
Liquid/Gas interface
Eulerian, diffuse-interface (i.e., pseudo-fluid)
Eulerian, Mixture Model
VOF Transport + interface compression
n/a (?)
Heat Transfer Enabled?
No; fuel is isenthalpic
No; isothermal
Liquid/gas interface  make point that only computing one velocity vector per cell

8. Computational Domain Institution/Code UMass HRMFoam ANL Converge
Delphi
PoliMi
Dimensionality 3
Cell Type
Polyhedral with extrusion layer
Cut-cell Cartesian Cubic Types
Hexahedra
Cell count (total interior and exterior)
414k
2.8 & 4.5 million
5.2 million
1.2 million
(GridPro)
Adaptive or Static Refinement?
Static
Needle motion? NO
Geometry
“Ideal” geometry with 3mm plenum
“Ideal” geometry with mainly 9mm plenum
1/8 CAD seat geometry + 4mm plenum
“Ideal” geometry with 9mm plenum
Different code resolutions
Engineering (UMass)
Mid (PoliMi)
High (ANL)
Very High (Delphi)
Mention that all contributions are ideal geometry
Needle motion will be measured by ANL later this year … noted in future work

9. Geometry & Meshes Available on ECN Website
Working with GridPro to finalize OpenFOAM grids for “measured” CAD geometry
GridPro Mesh
(9mm Ideal)
Used by PoliMi Team

10. Comparison of “Ideal” & “Measured” Geometry
Plenum #
Feature
Ideal
Measured 1
Inner hole inlet diameter after inlet radius 3
0.165 mm
0.170 mm, all holes 2
Inner hole exit diameter before exit radius 4
0.173 mm, all holes 3
Inner hole inlet radius of curvature
0 mm
0.005 mm, all holes 4
Inner hole exit radius of curvature 9
Outer hole inlet reverse radius of curvature
0.040 mm
estimate
0.080 mm 9 4 3 2 1
needle

11. Computational Meshes
UMass/GM
ANL
15 µm min. grid size

12. Computational Mesh
domain

13. Time Accurate ROI Profile?
Boundary Conditions
Institution/Code
UMass
ANL
Delphi
PoliMi
Time Accurate ROI Profile?
Yes No
Inlet
Time varying velocity
Constant Pressure
Time varying Pressure
Constant Pressure (?)
Wall BCs
L.O.W.
Log. Law
L.O.W. (?)
Needle motion?
Time accurate =used the ROI measurements to compute velocity inlet condition

14. Simulation Results

15. Hole Orientation & Numbering
Spray G Convention
CAD Geometry 2 3 4 5 6 7 8 1
Mention 5 needle guides and 8 holes  injectors are not fed symmetrically
Axis of symmetry between holes 1 & 5

16. Summary of Submissions
Terminology
Fuel  liquid + vapor
Ambient  non-condensable gas
Injector Coefficients
CD, Cv, Ca (individual hole & injector averaged)
Contour Plots
Goal: use these data to initialize external spray solvers
2-D Contour plots
Plot
X Axis Min, Max
Y Axis Min, Max
Hole exit cut planes
-2 to +2 mm
See following slide for example.
Counter -bore cut planes
See following slide for example
Spray cut plane
-4, +4 mm at z=2mm
Variable
Color Map Min, Max
Density (kg/m3) & Velocity (m/s)
0, round max value to nearest multiple of 100
Temperature (K)
Round min & max to nearest multiples of 100
Turbulent Kinetic energy (m2/s2)
Void Fraction
0 to 1

17. Injector coefficients
Hole #
UMass/GM
(ECN 3)
ANL
Delphi
Individual hole 1
0.47
0.53
0.60
Single hole analysis 2
0.52
0.61 3
0.58
0.54 4
0.55 5
0.50 6
0.51 7
0.48
0.57 8
Overall Injector CD
0.59 Cv
0.73
0.78 - Ca
0.69
0.68 CD
Highest flowing holes
Lowest flowing holes
Little consistency on hole-to-hole flow variability, possibly caused by:
Mesh resolution and asymmetry
Accuracy of flow separation
Inlet radius resolution
GM Measurement CD ~ 0.52

18. Mean Velocity (m/s) UMass/GM ANL PoliMi 1 2 3 4 5 6 7 8
Counter bore exit
Both approaches are showing a bias in the velocity field towards the injector axis that initiates at the hole exit and propagates to the exit of the counter bore
Some hole-to-hole variability is predicted

19. Internal Nozzle Flow Field
DELPHI
Inner bias of the velocity field is initiated at the inlet corner of the holes
ANL
PoliMi
UMass/GM

20. Entrainment of ambient gas into the counter bore
ANL
UMass/GM
DELPHI
Ambient gases mix with injected fuel
RANS results shows strong bias of fuel towards inner edge
LES result shows fluctuations in fuel that fill counter bore

21. “Effective” Plume Trajectory
Spray G Injector Geometry Specification
ANL
PoliMi
UMass/GM
DELPHI
Velocity magnitude used to ‘eye-ball’ trajectory of spray plume
~32o
~35o
~33o
~33o
37o
37o
37o
37o

22. Temperature (K) UMass/GM ANL 1 2 3 4 5 6 7 8
Mention that no plots from PoliMi & Delphi here
ANL results shows hotter ambient gasses (nominally 573 K) entrained into the outer edge of the counter bore

23. Turbulent Kinetic Energy (m2/s2)
UMass/GM
ANL 1 2 3 4 5 6 7 8
Turbulence is generated within the holes in the ‘separation’ region. The magnitude of TKE to the counter bore exit differs  possibly due to heat transfer (the team will test this)

24. Mixture Density (kg/m3)
UMass/GM
ANL 1 2 3 4 5 6 7 8
Mention that no plots from PoliMi & Delphi here
PoliMi results show density with fuel and fuel vapor only so not directly comparabe
Mixture density contours look qualitatively similar. Both codes show some hole-to-hole variation.

25. Void Fraction of Vapor UMass/GM ANL 1 2 3 4 5 6 7 8
Both codes show some vapor at the hole exit, but differ in the persistence of the vapor at the counter bore exit.

26. Additional representation of phase change
Vapor Mass Fraction
PoliMi
Vapor initiated at the hole inlet and eventually condenses at the counter bore exit

27. Down steam (2mm) Liquid Distribution
DELPHI
ANL
“Probability of finding liquid”
Z=2mm
Both simulation approaches show qualitatively similar structures

28. Teaser … Spray G2 Condition
Gas Mass Frac.
UMass/GM
Liquid Vol. Frac.
z=2mm
ANL
Flash boiling leads to increased plume angle  plume-to-plume interaction

29. Summary General findings Future Work
All modeling approaches show a inward bias in the velocity field internal to the nozzle
Modeling approaches were consistent in predicting entrainment of ambient gases within the counter bore
Modeling approaches differ in the prediction of vapor persistence due to flow separation at the hole entrance & turbulence levels at the exit of the counter bore
Very little consistency amongst models on hole-to-hole flow variability
Future Work
Exercise meshes from GridPro
Improve CAD geometry with recent experiments
Simulation of needle motion (ANL plans to measure)
Full presentation of Spray G2 results
Comparison to increasing experimental database
Invite more contributors!