The spray characteristics of a room-temperature jet flow generated by a fan spray injector under high ambient pressure were investigated to clarify the atomization process and provide fundamental information about overheated water and liquid nitrogen injection,which are difficult to analyze.Visualization of the flow field using high-speed backlight imaging was conducted,and a phase Doppler particle analyzer(PDPA)system was used to determine the droplets diameters and velocities.By examining spray jet flows with atmospheric and high ambient pressure injections,intensive turbulent mixing and entrainment at the gas-liquid interface were observed in the latter case.The results of the PDPA measurements indicate that the droplet diameters are smaller in higher ambient pressure injection cases and that the mean droplet velocity decreases.The effect of ambient pressure was incorporated into Webers liquid sheet breakup length model by including a fitting parameter,and the results obtained from this model agree well with the experimental results.Furthermore,the mean velocity was redefined to include the effect of ambient pressure,and it adequately described the dependence on the differential injection pressure when a fitting parameter was included.