Abstract: The high-speed flow of internal fuel in diesel fuel injector is easy to cause cavitation inside the nozzle, which affects the flow of fuel. It is very important to study the cavitation process of fuel in the nozzle. The flow characteristics of the nozzle under different inlet and outlet pressures is studied by experiments on the scale-enlarged visualization test bench. The experimental results show that the inlet pressure is constant, with the decrease in the outlet pressure, 1) during the no cavitation period, the discharge coefficient is basically unchanged; 2) during the cavitation developing period, cavitation becomes stronger and develops from the entrance of the nozzle to the outlet, the mass flow rate continues to increase and the discharge coefficient decreases; 3) during the cavitation saturation period, the mass flow rate maintains stable but the discharge coefficient continues decreasing. The inlet pressure of the nozzle does not affect the critical cavitation number of cavitation inception and cavitation saturation. The diameter of the nozzle does not affect the point of cavitation inception, but the point of cavitation saturation; as the diameter of the nozzle is larger, the more difficult it is to achieve the cavitation saturation, and the smaller of the critical cavitation number. The length of the nozzle affects the point of cavitation inception and cavitation saturation; the length of the nozzle is longer, the more difficult it is to occur cavitation and to achieve cavitation saturation, the critical cavitation numbers of both the cavitation inception and the cavitation saturation are smaller.

Key words: power machinery engineering, injector nozzle, cavitation process, cavitation number, experimental research