A numerical study on the in-nozzle flow and near-field spray dynamics of spirally grooved hole nozzles: Effects of injection pressure and length/diameter ratio

The nozzle geometry in internal combustion engines plays a critical role in determining cavitating flow characteristics, which affect in-cylinder atomization, combustion, and engine performance. In this study, the multi-phase flow inside and outside spirally grooved hole nozzles were simulated using the Volume of Fluid model coupled with the Discrete Phase Model. This approach allowed for detailed examination of how injection pressure and length-to-diameter (L/D) ratio influence cavitation and atomization. The results showed that the nozzles with spiral grooves structure can increase the near-field spreading angle of the jet, but cavitation can negatively affect the distribution of droplets by decreasing the radial velocity. Moreover, when the L/D ratio is decreased from 5 to 2.5, the radial momentum intensity of the internal flow increased by 80%, leading to enhanced atomization. Notably, increasing the injection pressure from 150 to 250 MPa and reducing the L/D ratio from 5 to 2.5 both achieved similar improvements in fuel atomization, resulting in a 10% reduction in the Sauter mean diameter of droplets. A lower L/D ratio enhances atomization by shortening the flow path and increasing the radial momentum ratio, whereas higher injection pressure improves atomization by increasing jet kinetic energy and enhancing fluid-air interaction.