Experimental and numerical study of cavitation inception phenomenon in diesel injector nozzles

In this paper the experimental and numerical methods were combined to investigate the critical conditions of cavitation inception in diesel injector nozzles. It was found that at the beginning of cavitation inception, the discharge coefficient presents a slight increase and then a special turning point appears which can therefore be taken as the critical point for cavitation inception. Effects of needle lift, length–diameter ratio, orifice inclination angle, back pressure, and scaled-up times on critical cavitation number were studied through the experimental method. Due to the difficulties in manufacturing, influence of inlet rounding radius was investigated by using the numerical simulation method. Based on all the experimental and numerical simulation data, a correlation of critical cavitation number with above 6 geometrical and dynamic parameters for nozzle flow was developed through statistical analysis using the Quasi-Newton (BFGS) and Universal Global Optimization (UGO) methods. The relative error between predicted results and experimental data is less than 7%. These results indicate that the derived expression has good accuracy to predict the start of cavitation.