End-of-injection fuel dribbling dynamics of multi-hole GDI injector

The fuel dribbling at the end-of-injection (EOI) transient is believed to be harmful to the emission performance. However, quantitative characterization and detailed explanation of the fuel dribbling process for GDI injectors are rarely reported, and the mechanism is not thoroughly understood. This study conducted a comprehensive investigation on the fuel dribbling process at the EOI transient for a multi-hole sac-type GDI injector using the high-speed X-ray phase-contrast imaging (XPCI) technique. Simultaneous visualization of needle bouncing, in nozzle flow, and fuel dribbling directly illustrated that the fuel dribbling process was strongly correlated with needle bouncing. Further quantitative analysis of dribble volume and needle bouncing showed that the fuel dribbling process could be divided into the pre-needle-bouncing stage and the needle-bouncing stage. Distinct mechanisms of the two stages were explained through the dribbling source and the driving force. For the pre needle-bouncing stage, the dribbling source was the residual fuel in the sac, and the driving force was the pressure difference between the sac and the ambient. For the needle-bouncing stage, the dribbling source was the fuel fed to the sac from upstream, and the driving force was the needle bouncing. Possible control strategies of fuel dribbling were also discussed according to the dribbling mechanisms of the two stages. A high injection pressure tended to increase the dribble amount but to reduce the dribble size and dribbling duration, which was believed to be overall favorable to restrain the adverse effect of fuel dribbling.