Effects of injection pressure and length-diameter ratio on the velocity and cavitation inside injector nozzle

Computational investigation was conducted to understand the effects of various parameters on nozzle flow and cavitation in a diesel fuel injector for a diesel engine. The effects of injector parameters were simulated for different conditions including the injection pressure, the outlet pressure, the position of the needle lift, and the length of the nozzle. Results show that some parameters have obvious influence on cavitation associated with nozzle flow. When the outlet pressure was constant, the velocity through the nozzle increased with the injection pressure, resulting in the cavitation at the injection pressure over 120 MPa. When the injection pressure was constant, the velocity inside nozzle decreased with the outlet pressure. As the needle tip moved closer to the bottom of minisac, the velocity inside nozzle decreased and the cavitation did not take place. The length of the nozzle hole had little effect on the velocity at inlet, but it affected the velocity distribution at outlet.