A Numerical Investigation of Transient Flow and Cavitation Within Minisac and Valve-Covered Orifice Diesel Injector Nozzles

Cavitating flow within diesel injector passages has been investigated numerically using the homogeneous equilibrium model (HEM), which uses the barotropic assumption and the variable speed of sound of the mixture. To apply the HEM, the KIVA-3V code was modified to implement a generalized equation of state, and injector needle movement is simulated by the arbitrary Lagrangian-Eulerian (ALE) approach and the snapper algorithm. It is demonstrated that the model can predict the effect of nozzle passage geometry on the flow structure and cavitation. The model is able to reproduce the transient fuel injection rate as a function of the needle lift profile. Special interest is focused on the transient behavior during the nozzle closing period, which shows that the fast decrease in flow rate can increase the cavitation in the nozzle passage. The effects of the pressure difference and environment pressure on cavitation augmentation at the end-of-injection were also investigated. Flow characteristics due to different shapes of the nozzle flow passage in axisymmetric single hole nozzles and multihole nozzle configurations (minisac and valve-covered orifice eight-hole nozzles) were compared with emphasis on the end-of-injection period.