In-Cylinder Fuel Distribution Measurements Using PLIF in a SI Engine 970509

To study the effects of various parameters on the fuel distributions, planar laser induced fluorescence(PLIF) was applied to an operating engine. Particularly, the effect of an air-shroud injector was investigated in the cold condition. Iso-octane was used as the fuel and gasoline(10%) was added as a fluorescing tracer. The fuel distributions during the whole processes of intake and compression were investigated at firing condition and analyzed qualitatively. In addition, flame images were acquired to understand the combustion characteristics.

In cold and fuel injection during intake valve closed conditions(IVC), a number of fuel droplets flowed into the combustion chamber in the early and middle stage of intake process and the sizes of droplets were smaller than several tens of μm at both injectors; regular dual stream(D/S) and air-shrouded(A/S). Considerable amount of droplets remained until the late stage of the compression process. In fuel injection during intake valve opened conditions(IVO), the droplets induced in the late stage of intake process were much bigger than those of IVC conditions. Big droplets greater than ≃100μm were distributed in large numbers. In part load and IVO conditions, the dispersion of droplets in the late stage of compression process was better in case of A/S injector compared with D/S injector.

In hot and IVC conditions, most of the fuel flowed into the chamber as the vapor state and in the late stage of compression, fuel vapor was uniformly distributed in large scales. But, in IVO condition, the droplets directly induced during the injection period had the similar distribution pattern with that in cold condition.