Atomization and breakup of cryogenic propellants under high-pressure subcritical and supercritical conditions

Recent results on the atomization and breakup of cryogenic propellants unde r high-pressure subcritical and supercritical conditions are surveyed. Cryo genic fluids were injected into various gases under both cold-now and hot-f ire conditions,and the results were visualized using flashlight photography and highspeed cinematography. In some cases, simulation fluids were used t o study atomization and breakup behavior. In others, hot-fire tests with li quid oxygen and gaseous hydrogen demonstrated now phenomena under realistic cryogenic rocket engine conditions. The visualizations reveal a remarkable difference between subcritical spray formation and evaporation and supercr itical injection and mixing. As chamber pressure approaches the critical pr essure, injection can no longer he regarded as simple "spray" formation, bu t rather as a fluid/fluid mixing process that can be extremely sensitive to small perturbations in pressure, temperature, local mixture concentrations , and initial injection conditions.