Regression Rate Enhancement of Hybrid Rockets by Introducing Novel Distributed Tube Injector

Low fuel regression rate is one of the major drawbacks of hybrid rocket motors. In this study, a novel injector concept is proposed to provide a substantial enhancement in the fuel regression rate. A tubular injector, Distributed Tube Injector (DTI), is inserted in the center of the cylindrical fuel port in order to tailor the oxidizer flow introduced into the combustion chamber with the desired combination of radial, tangential, or axial components of velocity. This concept has been tested using a 500 N thrust class hybrid rocket motor, which uses a paraffin-based fuel and supercharged N2O (L) as the oxidizer. As a result of 30 hot firings conducted in the test program, it is determined that the DTI configuration provides regression rates up to 3.9 times higher than the regression rates obtained using fore-end injector commonly employed in conventional hybrid rockets. Using the motor test data, a comprehensive nondimensional and scalable regression rate relation has been established. This nondimensional regression rate equation can be used to design the internal ballistic configuration of hybrid rocket motors using the novel injector.