Characterizing Propane Flash Boiling Spray from Multi-Hole GDI Injector

In this research, propane flash boiling sprays discharged from a five-hole gasoline direct injector were studied in a constant volume vessel. The fuel temperature (T_fuel) ranged from 30 °C to 90 °C, and the ambient pressure (P_amb) varied from 0.05 bar to 11.0 bar. Different flash boiling spray behavior compared to that under sub-atmospheric conditions was found at high P_amb. Specifically, at the sub-atmospheric pressures, the individual flashing jets merged into one single jet due to the strong spray collapse. In contrast, at P_amb above 3.0 bar and T_fuel above 50 °C, the spray collapse was mitigated and the flashing jets were separated from each other. Further analyses revealed that the mitigation of spray collapse at high P_amb was ascribed to the suppression of jet expansion. In addition, it was found that the spray structure was much different at similar R_p, indicating that R_p lacked the generality in describing the structure of flash boiling sprays. The results also revealed that the low-pressure zone induced by high-speed jet movement was compensated under flash boiling conditions, which confirmed that the mechanism of spray collapse under flash boiling conditions was different from that at non-flash-boiling conditions.