Effect of injection strategy on air-fuel mixing process in a gasoline direct injection (GDI) optical engine

Abstract

In the present study, a Gasoline Direct Injection (GDI) optical engine was used to investigate the spray development and the air-fuel mixing process for various injection strategies. By using single-cylinder optical engine, the effect of the intake flow, piston movement and shape of piston bowl on the spray development were considered. The present engine adopts wide side view quartz which can show about 40% of the stroke. Two metal-halide lamps were used as light sources, and they were placed on the left and right side of side view quartz. A high-speed camera was used to take the spray development sequence images. Experiments were conducted for various injection timings, engine speeds and injection pressures. The shape of the spray development was mainly affected by the injection timing. When the fuel was injected during the intake stroke, the air-fuel mixing process was stimulated by intake flow. However cases for the injections during the compression stroke, the air-fuel mixing process was only caused by the air entrainment. Based on the spray images, the engine speed itself did not influence the spray development. But as the intake flow became faster with the engine speed increases, the spray development process of the fuel, which was injected during the intake stroke, was stimulated by the intake flow. Because the process of the spray development can be observed directly via an optical lens, it became easier to determine the optimal injection timing.