OPTICAL ANALYSIS OF A GDI SPRAY WALL-IMPINGEMENT FOR S.I. ENGINES A. Montanaro, L. Allocca, S. Alfuso Istituto Motori CNR, Napoli Italy XV National Meeting, Milano 29-30 Novembre 2007
GENERAL CONSIDERATIONS Attention of International Community on pollutant emissions and life quality About 25% of energy consumption and greenhouse gas emissions are due to transportation The technological challenge in i.c. engines fields is to meet performances and consumption with emission regulations Sprays from high pressure electronically controlled injection systems are successfully used today both on diesel and gasoline engines For automotive engine size, the interaction of the fuel with the combustion chamber wall plays an important role in fuel atomization and its spatial distribution
Fuel supply systems evolution for SI engines
Gasoline Direct Injection (GDI) advantages in SI engine High fuel injection pressure better atomization High compression ratio Zero pumping losses Ignition process control Good cold starting characteristics Multimode operation: stratified and homogeneous charge
Stratified charge Homogeneous charge
The behaviour of the spray impacting on a hot surface, in terms of droplets fragmentation and spatial fuel distribution, influences the mixture formation during the ignition delay with effects on combustion process and pollutant production In this study is reported, for different injection and ambient conditions, an analysis of the sprays behaviour from a hollow-cone injector for GDI engine, impacting on a heated flat wall.
EXPERIMENTAL CONDITIONS - 1 Injected fuel EXXSOL D40 (T b = 162 C) Inj. pressure p inj Injection time [ms] Injected fuel -density: [MPa] ρ = 760 kg/m 3 (T = 40 C) [mg/str] - cinematic 6-8 -10 viscosity: ν = 1.05 1cSt (T = 40 6.95 C) 7.73 8.55 Injector: swirled-type with four rectangular fuel adduction channels - Inj. nominal pressure flow prate: inj Backpressure p amb 7.4 g/s Wall at 10 temperature MPa [MPa] [MPa] [ C] - nominal primary cone-angle: 60 6-8 -10 0.1-0.6-1.2 25-80 -150-200 - exit hole diameter: 0.55 mm
EXPERIMENTAL CONDITIONS - 2 Single-shot mode operation Optically accessible high-pressure vessel filled with inert gas (N 2 ) - gas pressure: 0.1 to 5.0 MPa - ambient gas temperature Stainless steel flat plate located at 22 mm from the nozzle tip on a x-z-ϕ positioning system - 200 W electrical heating system - temperature range: 300 500 K (+/- 1 K) - mean roughness: 1.077 μm (Rank Taylor Hobson profilometer) Nd-YAG pulsed laser sheet (100 μm thickness, 12 ns duration) PULNIX CCD Camera 768x568 pixels, 8 bit Image processing software
EXPERIMENTAL SET-UP
laser beam
Laser shooting
t=300 t=500 t=800 t=1000 μs μs p inj = 6.0 MPa p amb = 0.1 MPa = 25 C
P inj =10.0 MPa P amb =0.1 MPa =25 C p inj =8.0 MPa p amb =0.1 MPa =25 C p inj =6.0 MPa p amb =0.1 MPa =25 C t=300 μs t=500 μs t=800 μs t=1000 μs
P inj =10.0 MPa P amb =0.1 MPa =25 C p inj =10.0 MPa p amb =0.6 MPa =25 C p inj =10.0 MPa p amb =1.2 MPa =25 C t=300 μs t=500 μs t=800 μs t=1000 μs
P inj =10.0 MPa p inj =10.0 MPa p inj =10.0 MPa p inj =10.0 MPa P amb =0.1 MPa p amb =0.1 MPa p amb =0.1 MPa p amb =0.1 MPa =25 C =80 C =150 C =200 C t=300 μs t=500 μs t=800 μs t=1000 μs
width [mm] 80 75 70 65 60 55 50 45 40 =25 C =80 C =150 C =200 C P inj =10 MPa P amb =0.1 MPa 35 30 25 400 600 800 1000 1200 time after SOI [μs] Fuel width for different temperature of the wall
80 75 70 65 60 P inj =6 MPa P inj =8 MPa P inj =10 MPa P amb =0.1 MPa =25 C width [mm] 55 50 45 40 35 30 25 400 600 800 1000 1200 time after SOI [μs] Fuel width for different injection pressure
Spray cone-angle vs. backpressure spray cone angle [deg] 100 90 80 70 60 50 40 30 20 P inj = 10 MPa far cone angle near cone angle 0.0 0.6 1.2 P chamber [MPa]
CONCLUSIONS Time- and space-evolution of a hollow-cone spray, from a swirled injector and its impact on a flat wall, have been visualized varying the injection pressure, the backpressure and the temperature of the wall The image processing technique have enabled to obtain information on the shape, structure and morphology of the sprays The fuel distribution and vortexes of the spray impacted on the wall depend on injection pressure, backpressure and wall temperature configuration The wall temperature markedly influences the shifting and rebounding of the fuel droplets on the plate contributing to the mixture formation process
THANK YOU FOR YOUR ATTENTION OPTICAL ANALYSIS OF A GDI SPRAY WALL-IMPINGEMENT FOR S.I. ENGINES by A. Montanaro, L. Allocca, S. Alfuso XV National Meeting, Milano 29-30 Novembre 2007