Experimental investigation on the spray characteristics of a self-pressurized hollow cone injector

Influence of ambient pressure on spray characteristics of a special self-pressurized outwardly opening injector was experimentally studied. The experiments were conducted in a constant-volume vessel with the ambient pressure ranging from 5.0 kPa to 600 kPa. Spray characteristics such as spray tip penetration, width and dispersion area under different ambient pressures P_a were obtained using image post-processing method. The results reveal that spray pattern shows a “flash-boiling—typical—vortex” hollow cone spray transition corresponding to the non-monotonic spray dispersion area ratio tendency with ambient pressure increasing. Intense spray flash-boiling and resultant drastic morphology changes were observed under ambient pressure of 5.0 kPa and a distinct flash-boiling induced vortex-ring was first observed inner the spray, together with rapid evaporation and finally promoted spray dispersion. Typical hollow cone spray was observed with intermediate ambient pressures between 40 kPa and 200 kPa. Jet-string structure was formed on the surface of typical hollow cone spray due to air disturbance and surface tension of the liquid-sheet jet. When P_a>400kPa, notable spray induced vortex was formed with enhanced entrainment of the airflow, which contributes to liquid droplet movement therefore again promotes spray dispersion.