Spray impingement characterization of a swirl type injector for gasoline direct injection engines

Abstract

Engine efficiency and emissions depend on the initial fuel spray, evaporation, mixture preparation and distribution inside the chamber. This phenomenon is based on the interaction of the in-cylinder air motion, tumble or swirl. One drawback of the gasoline direct injection (GDI) engine is that the spray impingement on the piston and cylinder wall often leads to high emissions of unburned hydrocarbons and soot. To further understand the spray impingement characteristics that are related to the GDI engine performance of economy, emission and the combustion, the sprays into constant volume chamber within a flat wall installed under different back pressure value from a swirl type GDI injector were visualized. The spray impinging development, spray penetration at normal and radius direction of wall, spray tip velocity and droplet characteristics were measured at various injection pressure, ambient back pressure, wall distance from the injector tip to the impinging wall, and wall inclination angle. Experimental results showed that the spray structure exhibited a large hollow cone angle and wide spreading at low back pressure, therefore the fuel film adhered on wall after being impinged is thin and it is favourable for fuel evaporation and diffusion, however, it is unfavourable for fuel evaporation and diffusion under high back pressure. The spray growth velocity is sharply decreased, also the spray height and spray radius growth rate decreased after impingement of the spray. Impinging sprays exhibit longer spray penetration behaviour at normal and radius direction of the wall under higher injection pressure, shorter wall distances and larger angles of wall inclination. The spray height and spray radius decreased with the increase of ambient pressure. Higher injection and lower ambient pressure promote an increase of the spray area, and causes more rapid movement of the spray. Higher ambient pressure slows down the spray movement. The formed vortexes under high back pressure become one of factors that increase the spray height and decrease the spray radius and spray tip velocity growth rate. (6 pages)