Influence of flash boiling on spray morphology using a prototype injector for gasoline compression ignition (GCI) application

Flash boiling occurs with gasoline direct injection spray at throttling, and low load engine conditions leading to plume interactions and sprays collapse under low ambient densities. The change of fuel trajectory compared with the injector's initial design could leave an adverse effect on spray combustion quality, although flash boiling has the potential of achieving better atomization. Thus, the study of the plume to plume interactions and spray collapse processes are of high importance. Researches have mostly been carried out focusing on the plume interactions in the liquid phase. While in the flash boiling condition, the vapor phase of fuel is non-negligible. This work focusses on the plume to plume interactions considering both the vapor and liquid phase of the fuel under specific throttling conditions in gasoline compression ignition (GCI) engines using a high-pressure wide spray angle prototype injector. The experiments were carried out at a wide range of pressure ratio (Rp) conditions (Rp = 0.05 to 1.4). Simultaneous front view and side view shadowgraph techniques were implemented to visualize the vapor phase of the fuel spray. Similarly, simultaneous front view Mie scattering and side view DBI (Diffused Backlit Illumination) techniques were implemented to visualize the liquid phase of the fuel spray. Due to the line of sight plume overlapping at the side view, the difference in spray morphology obtained by DBI and shadowgraph is not apparent. However, the front view comparison shows that, in the transition regime, the plume to plume interactions in the vapor phase is more evident than that in the liquid phase.