Performance characterization of the hybrid rocket motor with secondary injection

The nature of the large diffusion flame in the classical hybrid motor results in poor mixing and low combustion efficiency. Introducing a secondary- injection of the oxidizer into the aft mixing chamber is an attractive method to enhance the performance. The hybrid rocket motor with secondary injection is identical to the classical with an added aft oxidizer system. A portion of the oxidizer required for proper mixture ratio operation is primary' injected into the head end of the fuel grain. The remainder of the oxidizer is bypassed and secondary injected into the aft mixing chamber. In this paper, a CFD code is used to simulate the combustion flow field and performance characterization of the hybrid rocket motor with secondary, which applying 90% hydrogen peroxide (90%H202) as the oxidizer and hydroxy 1 terminated polybutadiene (HTPB) as the fuel. The three dimensional temperature contours, species distributions, regression rate and performance of the hybrid rocket motor are obtained. The results show that the secondary injection doesn't affect the flow field of the pre-chamber and fuel port. The O/F changes quickly when the secondary oxidizer mass flow changes and a nearly constant mixture ratio can be easily maintained at all times during motor operation. The injection of a portion of vaporized oxidizer into the aft mixing chamber is helpful in the combustion of certain unburned fuel species. The characteristic velocity (C*) and combustion efficiency can be improved evidently with secondary injection. When the primary oxidizer mass flow is 0.4 kg/s and the secondary oxidizer mass flow is 0.3kg/s in this research, the C* is raised up to 1625m/s and the combustion efficiency is increased at 97.43%.