Study of the effect of nozzle hole shape on internal flow and spray characteristics

The presence of cavitation and turbulence in a diesel injector nozzle has significant effects on the subsequent spray characteristics. In this paper, the influence of nozzle hole shape on internal flow and near-nozzle spray behavior at stationary conditions was studied. A flow visualization experimental system with a transparent scaled-up injector was setup. Three min-sac nozzles with the same hole outlet diameter but different hole shapes (cylindrical, convergent, and divergent) were used for the investigation of influence of nozzle hole shape on internal flow and spray. A detailed comparison of the cavitation and spray characteristics of the three nozzles was conducted under a variety of fuel injection parameters. Results show that cavitation collapsed inside the hole leads to an increment of flow turbulence but has limited effects on spray cone angle. However, when cavitation extends to the hole outlet, the spray cone angle increased sharply. These results indicate that the collapse of cavitation bubbles contributes to the disintegration of the spray mainly through causing a local breakup. Furthermore, the hydraulic flip phenomenon was also investigated.