gasoline direct injection in si engines
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Gasoline Direct Injection in SI engines
Petter Dahlander, Ronny Lindgren and Ingemar Denbratt Chalmers University of Technologyy gy
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Purpose of investigation
• How do the fuel distribution vary for different nozzle hole configurations?
Symmetrical Asymmetrical
• How do the fuel distribution vary for different nozzle hole configurations?1. Symmetrical 2. Asymmetrical
• Identifying factors that cause the difference y g• How can certain injector parameters be used to control the spray?
1. Fuel cloud coherency2. Cross-flow velocity3 Spray induced turbulence?3. Spray-induced turbulence?
• Spray cycle-to-cycle variation?
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Challenges for stratified operation of a spray guided GDI combustion systemspray-guided GDI combustion system
• Ignitable mixture at the spark plug at g p p gthe time for ignition (ø≈1 or slightly rich)
• Ignite too early:y Soot formation
• Ignite too late:y Too lean mixturey UBHCy UBHC
• Reasonably wide ignitibility window• Misfire free operation
Stable combustion• Stable combustion• Minimize wall wetting
y UBHC, PM emissionsE h f Image from www autospeed com
• Exhaust aftertreatment
”Ideal” fuel cloud difficult to realize!
Image from www.autospeed.com
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Nozzle configurations
Umbrella angle
Symmetrical Asymmetrical(”horseshoe”)
1 2 3 4Config. Symm. Symm. Asymm. Asymm.
(”horseshoe”)
Hole diameter (microns) 101 101 101 101
l/d 10 10 10 10
Main gap 60 60 160 120
Individual gap 60(x6) 60(x6) 40(x4) 45(x4)
Injector spark gap 60 60 40 60
Umbrella angle 70 85 85 85
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Experimental setup p p
Numerical setup Heated/pressurized spray chamber:
p• AVL Fire v8.3• Spray break-up and atomization modeled with the Kelvin Helmholtz/Rayleigh Taylor
• PLIF/PMie• PDI• High-speed camera
with the Kelvin Helmholtz/Rayleigh-Taylor Hybrid model• Drop collisions and coalescence not modeled• Fire’s models for evaporation, drag, and
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g p Fire s models for evaporation, drag, and turbulent dispersion
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Boundary conditionsBoundary conditions
• Fuel: Iso-octane with 10% dietylketon• 25 MPa fuel pressure• 25 MPa fuel pressure• 1 MPa/600K ambient pressure/temp• PLIF/PMie/PDI/High-speed camera/CFD
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Droplet atomizationDroplet atomization
(Spray plume core, z=20 mm)
• High fuel pressure and small holes gives small droplets
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Spray-induced air motion (CFD)Spray induced air motion (CFD)(Results for nozzle 1 is displayed)
0.3 ms ASOI 0.9 ms ASOI 1.8 ms ASOI
Spray induced air motion gives air entrainment Spray-induced air motion gives air entrainment from both the side and from below
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Near nozzle air entrainment (CFD)(horisontal cut 10 mm from nozzle)( )
Increased air entrainment on the open side of the horseshoe
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Fuel distributionS t i l A t i lSymmetrical Asymmetrical
Liquid+Vapor(during injection)
Vapor(after injection)
• More coherent fuel clouds• More coherent fuel clouds• Better air entrainment• ”Gap” provides a way to control cross-flow
velocity and turbulence
• Discrete fuel clouds
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Fuel distribution (vapor) – Cycle-to-cycle
Nozzle 1 Nozzle 2
Nozzle 3 Nozzle 4
11 • Cycle-to-cycle variations could be one reason for random misfires
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Cross-flow velocities in the spark plug plane(vertical cut, CFD)
Nozzle 1(Symmetrical )
Nozzle 2(Symmetrical)
Nozzle 3(Asymmetrical)
> A small injector spark plug gap gives -> A small injector spark plug gap gives much higher cross-flow velocities
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Spray-induced turbulence in the spark plug plane (CFD)Spray induced turbulence in the spark plug plane (CFD) - Effect on the turbulent kinetic energy of varying the injector spark gap
Nozzle 2Injector spark gap=60 degrees
Nozzle 3Injector spark gap=40 degrees
(Nozzles 2 and 3 have the same umbrella angle)-> Small injector spark gap increases spray induced turbulence
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ConclusionsCo c us o s
Many parameters to control the spray• Many parameters to control the spray• Horse-shoe shaped configuration gives better air entrainment
and better fuel cloud coherencyy• Symmetrical nozzles tend to result in isolated fuel clouds• Distance between spray plumes in spark plug plane control
y Fuel cloud coherencyy Cross-flow velocityy Turbulence
• Always partially premixed fuel cloud• Cycle-to-cycle variations can be a reason for random misfires
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Acknowledgementsc o edge e s
• CERC (Combustion Engine Research Centre at CHALMERS)CERC (Combustion Engine Research Centre at CHALMERS) for financial support
• Volvo Car Corp & GM for technical supportVolvo Car Corp & GM for technical support • Statoil
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