Mixing Characteristics of Coaxial Injectors at High Gas/Liquid Momentum Ratios

Abstract

A study of the spray of a swirl coaxial gas-liquid injector operating at high-liquid momentum ratios is reported. Mixing and droplet size characteristics of the swirl injector are also compared to a shear coaxial injector, currently being used in the space shuttle main engine fuel preburner. The injectors were tested at elevated chamber pressures using water as a liquid oxygen stimulant and nitrogen and helium as gaseous hydrogen simulants. The elevated chamber pressure allowed for matching of several of the preburner injector conditions including gas/liquid momentum ratio, density ratio and Mach number. Diagnostic techniques used to characterize the spray included strobe backlight imaging, laser-sheet spray imaging, mechanical patternation, and phase Doppler interferometry. The results indicate that the radial spreading of the swirl coaxial spray is much less than was reported in previous studies of swirl injectors operating at atmospheric backpressure. The swirl coaxial spray did, however, exhibit a smaller overall droplet size.