Experimental Study On The Process Of Cavitation And Its Influence On The Nozzle Of Diesel Engine

Nozzle in diesel engine as the terminal of injection system has a decisive influence on the quality of flue spray, the coordination of fuel beam and combustion chamber, and the length of the fuel injection duration, and directly affects the quality of combustion in cylinder. The spraying quality of nozzle is one of the important factors that influence the performance of d iesel engine. Good atomizing effect can improve the performance of diesel engine power and reduce the emission of harmful emissions, and improve the fuel economy. There are many factors that affect the fuel spray mixing characteristics, among which the effect of cavitation in the fuel injector on the working characteristics of the injector is particularly prominent. The high speed flow of internal fuel in diesel fuel injector is easy to cause cavitation inside the orifice, which can influence the circula tion capability. It is of great significance to study the process of fuel cavitation in the injection hole.The spray hole as the research object, in the proportion of enlarged transparent nozzle visualization test bench by the K istler pressure sensors to measure the inlet and outlet pressures. The fuel mass flow rate is measured by the fixed time weighing method. The optical test of the nozzle inner flow characteristics is observed by using a high-speed video camera and long-working-distance microscopic imaging technology. The optical test is completed under different inlet and outlet pressures. The nozzle cavitation characteristics and the mass flow rate are studied. The experimental results show that when 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 d ifficult 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.