Experimental Study of a Combined-Cycle Engine Combustor in Ejector-Jet Mode

Abstract

*† ‡ § § A combustor model of a rocket-ramjet combined-cycle engine was tested in an ejector-jet mode under a sea-level, still condition. The model had two rockets in the duct. Propellants were gaseous hydrogen and oxygen. Design factors of the combustor were cross sections at the entrance and the exit, length of the combustor, fuel injection position and rocket operating conditions. In the tests, the designed operation of the ejector-jet was successfully attained. That is, breathed air was choked at the throat section. Supersonic rocket exhaust and air were decelerated in the divergent duct with an increase of the wall pressure. Fuel was injected in the downstream straight section and combustion gas choked at the exit. Mean Mach number was unity, and mean combustion efficiency was 0.8 according to pitot pressure measurement and gas sampling. Thrust augmentation was confirmed with the measurements. Operating conditions predicted in the design process reasonably agreed with those in the experiment. Other design factors were also investigated. Suction performance was increased with increase of a mixture ratio of the rockets. Acceleration of the breathed air was affected by length of the upstream straight section. The combustion status was not affected by length of downstream straight section or position of fuel injection. Fuel increase caused an increase of the pressure until a stoicheometric condition.