Investigation of mixture-ratio distribution in a liquid rocket engine



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This study is concerned with the application of an analytical technique to the solution for thermodynamic properties in the exhaust plume of a liquid-propellant rocket engine. The engine selected for analysis was the Apollo Lunar Module-Reaction Control System motor which is used to supply pitch, yaw and roll control for the Lunar Module during descent and ascent from the lunar surface and during docking maneuvers. The engine was test fired in a vacuum chamber with a back pressure corresponding to 96,000 feet altitude, and pitot pressures and stagnation heating rates in the plume were measured. This study was initiated in an attempt to match analytically the experimental data. After this was accomplished, the same initial engine conditions could then be used in performing calculations for expansion into a vacuum. These vacuum calculations could then allow predictions for engine firings and related events in the lunar environment to be performed with a high degree of confidence. The preliminary calculations, in addition to physical engine configuration, indicated the presence of a mixture-ratio distribution across the nozzle. Thus, calculations were begun in an attempt to find a mixture-ratio distribution which would produce matching of the experimental data. There was no single mixture-ratio distribution found which produced good agreement between both the pressure and heating rate data. However, it was concluded that a mixtureratio distribution which was nearly constant (2.6 on the axis, varying linearly to 2.5 on the wall) was very representative of the real engine. This distribution can be used with high confidence to predict the engine exhaust-plume thermodynamic properties in the lunar environment.