Experimental investigation of a flow-oriented throttleable injector designed for throttleable hybrid rocket motor

Easily achieving thrust throttling is a significant advantage of hybrid rocket motor. To achieve more stable combustion and reduce the pressure of the upstream feed system during the thrust throttling, it is necessary to control the injection conditions while controlling the oxidizer mass flow rate. In view of this, a flow-oriented throttleable injector that can control the injection pressure drop during the thrust throttling was designed, fabricated and tested. In order to verify the feasibility and obtain the injection pressure drop characteristics, cold flow tests of the flow-oriented throttleable injector were performed, including static injection pressure drop tests with/without back pressure and dynamic injection pressure drop tests with/without back pressure. Then, the steady-state hot test and thrust throttling hot tests of the throttleable hybrid rocket motor with the flow-oriented throttleable injector were conducted, in which the 98%H2O2/PE were adopted as the propellant combination and the controllable cavitating venturi was used to control oxidizer mass flow rate. In thrust throttling tests, the achieved maximum of the thrust throttling ratio was 8.65 under the condition that the change ratio of oxidizer mass flow rate was 7.19. During the thrust throttling, the motor worked stably, and the combustion chamber pressure, thrust and injector pressure drop varied approximately linearly with the linear variation of the oxidizer mas flow rate. The variation of injection pressure drop of the flow-oriented throttleable injector was much less than that of the conventional fixed structure injector, of which the injection pressure drop is proportional to the square of the oxidizer mas flow rate.