Direct injection of fuel into the engine cylinders has been regarded as a way of reducing fuel consumption and pollutant emissions. The spray generated from the direct injector is of paramount importance in gasoline direct-injection (GDI) engines in that the primary atomization process must meet the requirement of quick and complete evaporation with proper mixing followed by combustion especially to prohibit excessive hydrocarbon (HC) emissions.
The interaction between air flow and fuel spray was investigated in a steady flow system embodied in a wind tunnel to simulate a wide range of flow conditions inside the cylinder of the GDI engine. Direct Mie-scattered and shadowgraph images present the macroscopic view of the liquid sprays and vapor fields. The velocity and particle size of the fuel droplets were investigated with a phase Doppler anemometer (PDA) system. The processes of atomization and evaporation with a GDI injector were observed and consequently utilized to construct a database for the spray and fuel-air mixing mechanism as a function of the flow characteristics. Fuel vaporization was found to be proportional to crossflow velocity. Air entrainment in the vortices was found to be still active in a strong flow field.