Analysis of Fuel Flow and Spray Atomization in Slit Nozzle for Direct Injection SI Gasoline Engines

The slit nozzle in the fuel injection valve for a direct injection spark ignition gasoline engine forms a thin, fan-shaped spray. The fan-shaped spray is characterized by high dispersion, comparatively high penetration, and fine atomization. This enables it to form a stable air-fuel mixture. However, further improvement of engine performance requires that the spray characteristics (particularly the level of atomization) be improved. Since the spray characteristics are strongly influenced by the fuel flow within the nozzle, it was clarified this effect by visual analyses of the fuel flow inside the nozzle using enlarged acrylic slit nozzles. The results demonstrated that vortices that are formed within the nozzle sac are continuously propagated in a periodic manner within the sac and that they influence the streamline of fuel flow from the sac to the slit. It was also demonstrated that the smaller the vortices that form in the sac, the thinner the liquid film that forms at the edge of the slit. This enlarges the region in which cavitation occurs in the central portion of the slit, thereby improving atomization.