INVESTIGATION OF THE EFFECTS OF VORTEX-INDUCED STRING CAVITATION ON FLOW AND SPRAY CHARACTERISTICS WITHIN DIESEL FUEL INJECTION NOZZLES

The diesel fuel injection system relies heavily on the precise operation of the fuel injection nozzle, universally recognized as its foundational component. A key factor significantly affecting both flow capacity and injection performance is the internal flow characteristics of the nozzle. This study investigates the vortex-induced string cavitation within fuel injector nozzles by incorporating high-speed imaging, particle image velocimetry techniques, and numerical simulations. The results demonstrate that an increase in injection pressure precipitates an escalation in string cavitation intensity, thus reducing the effective flow area and compromising internal flow capacity. Importantly, our study confirms that, despite its intensified occurrence under higher pressure, string cavitation does not cause significant erosion damage. Instead, it plays a pivotal role in promoting fuel atomization by injecting it into a rotational state, facilitated by the cyclonic action within the nozzle. Furthermore, our observations reveal a notable distinction between needle-hole string cavitation and hole-hole string cavitation. Specifically, needle-hole string cavitation produces more extensive spray angles compared to hole-hole string cavitation. However, it is crucial to note that the former exhibits reduced uniformity in the distribution of velocity fields and a weakening of the jet atomization effect. In conclusion, this comprehensive study provides valuable insights into the intricate mechanisms of string cavitation. Through an exhaustive exploration of flow characteristics, erosion effects, and atomization processes, our work significantly contributes to the field of fuel injection system engineering.