Study of Mixture Formation in Engine Cylinder by Image Analysis of Schlieren Observation

A single cylinder visualization engine with the TCC (transparent collimating cylinder) was applied to the study of a direct-injection gasoline engine. Fuel sprays, mixture forma-tion and combustion process in the cylinder were observed using the schlieren method. The schlieren images were analyzed by image analysis technique. The shapes of the fuel spray are drastically changed with the injection timing ; namely oval shaped when in-jecting during the suction stroke, conical shaped when injecting near BDC, and bell shaped when injecting during the compression stroke. The fuel/air mixture formations also change with the injection timing. When the injection timing is late, the mixing of fuel and air is also late and the luminous region in the schlieren image of the mixture be-comes clear. In the case of the injection timing of 60 deg. before TDC, the injected fuel spray impinges on the top of the piston and the fuel/air mixture exists around the top of the piston, so that miss fire and abnormal combustion occur.