Investigation of a Ducted Rocket with a Paraffin/Oxygen Hybrid Gas Generator

Abstract

Analysis and testing of a ducted rocket employing a hybrid gas generator is presented. Over 150 successful static firing tests have been performed using a connected pipe facility supplying vitiated air to the ram combustor at stagnation temperature and pressure encountered in actual flights. The hybrid gas generator consisting of paraffin wax and gaseous oxygen operated unchoked, supplying hot, fuel-rich gases to the ram combustor for further burning with air. Empirical correlation of the fuel regression rate versus oxidizer mass flux in the gas generator has been displayed, and good overall combustion efficiency has been revealed. Thrust and fuel/air ratio control via the cold oxidizer flow rate into the gas generator is a major advantage of employing a hybrid gas generator. It was shown that such control could be done over broad ranges of flight altitude, flight Mach number, and thrust, while maintaining the ram pressure throughout the engine. This is in contrast to the thrust control of a ducted rocket employing a fuel-rich solid propellant. In that case, the process involves variation of the gas generator nozzle throat area by a mechanical device within the hot flow, implying a large increase of pressure in the gas generator combustor. Different scenarios of engine control and thrust modulation for variable flight conditions and requirements have been demonstrated.