Influence of hydraulic flip on spray uniformity and dynamics in Gasoline Direct Injection nozzles

Gasoline Direct Injection (GDI) nozzles are widely used in modern engines to improve fuel efficiency and reduce emissions by achieving better atomization and combustion. Their compact length-to-diameter (L/D) ratio facilitates spray breakup and induces hydraulic flip, a phenomenon that significantly influences spray plume orientation and spray characteristics. However, the effect of hydraulic flip on the uniformity of spray characteristics remains poorly understood. This study investigates how hydraulic flip influences spray uniformity using X-ray phase-contrast imaging to visualize internal flow and its effects on spray dynamics in two test nozzles. The findings show that hydraulic flip is governed by the inlet radius-to-diameter ratio and interval angle. In the Base nozzle (without hydro-grinding processing), hydraulic flip widths differ by 11.3 % between holes due to the inlet interval angle. In contrast, the HG nozzle (with hydro-grinding processing) exhibits a larger difference of 41.6 %, influenced by both the inlet radius-to-diameter ratio and interval angle. Hydraulic flip significantly affects droplet size and velocity distributions. Increasing injection pressure from 80 to 200 bar reduces peak droplet size by 8.6 % in the Base nozzle and 14.4 % in the HG nozzle. Suppressing hydraulic flip in the HG nozzle enhances spray uniformity, while delaying droplet breakup. These insights support the optimization of GDI nozzle designs for improved combustion and emissions control.