Abstract: Spray droplet size is one of the important parameters to evaluate the spray characteristics of injector, and is also one of the significant boundary conditions of the engine combustion system. In this paper, the spray droplet size characteristics of Gasoline Direct Injection (GDI) engine is studied using laser diffraction technique under the conditions, such as different spray pressure, injection pulse width and space position. The results demonstrate first, the big size droplet is prone to occur due to the unstable pressure difference between the inner and outer of the orifice at the beginning and end of spray; second, the influence of spray pressure and injection pulse width on the droplet size is a dynamics process, therefore, it is important to optimize the injector's parameters to obtain appropriate spray droplet size; third, spray droplet distribution in the space is not uniform and droplet size in the center field of the spray plume is bigger than that in the boundary field.

Key words: power machinery and engineering, gasoline direct injection, spray, droplet size, laser diffraction