Visualization analysis of relationship between vortex flow and cavitation behavior in diesel nozzle

In diesel engines for passenger cars, the spray and combustion characteristics are one of the important factors for determining the exhaust and engine performances. These characteristics are affected by the internal flow, the film-type and string-type cavitations in the diesel nozzle. Specifically, the string-type cavitation correlates well with the spray cone angle, and the string-type cavitation behavior destabilizes the spray formation and combustion. The string-type cavitation is influenced by the vortex flow in the nozzle sac. Therefore, it is important to clarify the effect of nozzle and needle shapes on the vortex flow for further development of the diesel injector. This study investigates the effect of needle tip shape on a vortex flow, string-type cavitation and the spray characteristics. This was realized by comparison of the three needle shapes which were chosen in order to control the vortex flow in nozzle sac. A real-size transparent nozzle technique was used to investigate the relationship between the vortex flow and cavitation behavior in the diesel nozzle. This technique allows a spray characteristic to be observed concurrently with the inner flow as well. In addition, the visualized vortex flow was analyzed in detail by the micro-particle image velocimetry method and computational fluid dynamics.