Injection and Mixing Processes in High-Pressure Liquid Oxygen/Gaseous Hydrogen Rocket Combustors

Abstract

The injection, mixing combustion processes in a liquid oxygen (LOX)/gaseous hydrogen (GH2) rocket engine combustor at high chamber pressures (10 MPa) are studied and modeled. An experimental LOX/GH2 rocket motor consisting of a single coaxial shear injector element and a cylindrical chamber with optical access has been used for flow visualizations and measurements. Cold-flow injection test utilizing liquid nitrogen and gaseous helium at elevated pressures have been done for flowfield characterization by different diagnostic methods such as flash-ligth photography and high-speed cinematography using a shadowgraph setup. The injection visualizations and studies under cold-flow and combusting conditions revealed a remarkable difference between subcritical spray formation and evaporation and the supercritical injection and mixing process. The study shows that aproaching supercritical chamber pressures injection can no longer be regarded as a spray formation but rather as a fluid/fluid mixing process. As the flow visualizations indicate, the effect of the coaxial atomizer gas is less effective as previously expected. The flame is attached to the LOX post and develops in the LOX post wake. The observed flame holding mechanism is discussed. An evaluation of the radiation spectrum of the flame inside the combustion chamber revealed that radiation in the visible range is mainly due to water vapor.