MMH/NTO injection and ignition in vacuum downstream from an Aestus engine single injection element

An experimental study of the injection and ignition of MMH and NTO propellants injected under vacuum conditions downstream from an Aestus rocket-engine single element injector was undertaken to investigate the physical phenomena occurring during the first steps of injection and ignition in the actual conditions of the Aestus engine. A laser sheet technique was used to visualize the phenomena in a windowed combustion chamber, connected, through a sonic throat, to a vacuum tank. The injector and the combustion chamber were equipped with large bandwidth temperature and pressure transducers to follow accurately the unsteady phenomena. The paper describes the injection of each propellant injected alone and then their ignition when they are injected together. The low pressure conditions (200 hPa) have no influence on the MMH injection. On the contrary, the NTO spray is strongly modified when injected in vacuum (5 hPa). Ignition is always smooth because of the oxidizer injection lead procedure used and totally ruled by the MMH flow rate. Finally, because of the oxidizer injection lead procedure, frequent pre-ignitions between MMH and NTO vapor are observed in the MMH manifold when this valve is opened. According to the experimental conditions, these pre-ignitions are smooth and limited or steep.