Numerical investigation of the effects of nozzle geometry on internal cavitation flow and near-field spray

This study introduces the jet breakup ratio as a quantitative metric for spray characterization, examining the effects of nozzle sac chamber height, needle seat inclination angle and orifice inlet rounding radius on the in-nozzle cavitation flow and near-field spray features. A comparative analysis was performed on cavitation regimes and fuel jet breakup ratios at the same flow rate, with varying nozzle sac chamber heights and needle seat inclination angles. Results reveal that increasing the nozzle sac chamber height or decreasing the orifice inlet rounding radius significantly boosts the orifice flow rate. Conversely, changes in needle seat inclination angle have minimal effect on flow rate. Adjustments to nozzle sac chamber height, needle seat inclination, or orifice inlet radius modify internal flow dynamics, thereby optimizing jet atomization and spray quality. When the sac chamber height is appropriately set, intense vortex-induced cavitation occurs inside the nozzle, greatly enhancing spray atomization, the mean jet breakup ratio is increased by 6.4 % compared with the original nozzle configuration. Enlarging the needle seat inclination angle while keeping orifice dimensions constant maintains flow rate and improves spray quality through asymmetric flow destabilization, the mean jet breakup ratio is increased by 6.3 %. Reducing the orifice inlet rounding radius significantly amplifies geometrically-induced cavitation, aiding jet breakup and atomization, the mean jet breakup ratio is increased by 1.0 %. However, excessive cavitation increases cavitation erosion risks and can paradoxically decrease flow rates. Overall, these findings demonstrate that carefully controlling in-nozzle cavitation regimes is vital for optimizing nozzle performance. The jet breakup rate serves as an effective quantitative tool for assessing spray enhancement mechanisms.