Measurements of shear coaxial injector sprays: Cold flow and hot fire experiments

The propulsion community still does not completely understand the physical makeup of the determining factors for combustion stability of liquid rocket motors. Many experiments conducted with single element coaxial injectors within the past five years simulate the propellants of actual rocket engines with air and water but none operate at conditions close to these engines. Most experiments that simulate the propellants with GN₂/LN₂ or GH₂/LOX are within the operating conditions of actual engines. Experiments over the past year have focused on a hot-fire combustion chamber utilizing GH₂/LOX with one full-size SSME preburner element. The injector experienced full scale LOX flow rates and oxidizer/fuel mixture ratios between 2.2 and 5.6. LOX droplet sizes and velocities were measured with an Aerometrics Phase Doppler Particle Analyzer for chamber pressures between 300 and 800 psia. The first ever measurements of LOX droplet sizes above the critical pressure of pure oxygen were obtained. Droplet sizes decreased while droplet velocity increased for increasing gas/liquid velocity ratios while increasing the chamber pressure reduced the droplet size. A pressure modulation system and magnetic flowmeter were implemented on the chamber to analyze the velocity and pressure oscillations within the chamber.