Gasoline Direct Injection in SI engines

Petter Dahlander, Ronny Lindgren and Ingemar Denbratt Chalmers University of Technologyy gy

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

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

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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