Study of spray collapse phenomenon at flash boiling conditions using simultaneous front and side view imaging

Flash boiling has become a topic of interest to researchers due to its potential of achieving good fuel atomization and negative influence on GDI engine emissions when spray collapses and spray-wall impingement exists. Under flash boiling conditions, the accompanying spray collapse phenomenon and plume interaction are not clearly elucidated. Simultaneous side view diffused back illumination (DBI) and front view Mie-scattering were implemented in this work to capture transient plume to plume interaction of iso-octane fuel spray from a 10 hole gasoline direct injection (GDI) injector at flash boiling conditions. Fuel temperature and ambient gas pressure were varied in a wide range to cover collapse, transitional and non-flashing regimes. Two new criteria named ‘spray collapse percentage’, defined based on the front view Mie-scattering technique and ‘optical thickness’ based on the side view DBI technique, were developed for classification of different spray regimes. These two criteria distinguish the collapsing and transitional regimes well from the non-collapsing regime compared to other criteria used in the literature.