Cavitation in Fuel Injection Systems for Spray-Guided Direct Injection Gasoline Engines

Cavitation formation and development inside various types of nozzles for close-spacing spray-guided fuel injection systems is predicted using a computational fluid dynamics cavitation model. The fuel injection systems investigated include generic geometries of multi-hole nozzles and outwards opening pintle injectors. Model validation is performed against experimental data reported elsewhere in large-scale transparent nozzle replicas. The results confirm that cavitation strongly depends on the geometry of the nozzle and the operating conditions. For multi-hole nozzles, cavitation structures similar to those realised in Diesel injectors are formed. These include the needle seat cavitation realised at low needle lifts, the geometrically-induced hole entry cavitation and string cavitation developing inside the sac volume. A more chaotic and less understood cavitation pattern develops at the sealing area of inward seal band outwards opening nozzles. Vapour pockets have been found to develop around the circumferential area of the needle sealing area in a transient mode. Parametric studies obtained under realistic injection and back pressure conditions reveal the effect of nozzle design on the different nozzle flow patterns that may form during the injection timing.