Effect of Oxidizer Injector Swirl Angle on Hybrid Rocket Performance with Additively-Manufactured Fuel

With the emerging need for high-speed unmanned aircraft that operate without a runway, there is a critical need for a low-cost, reusable, and safe rocket-assisted takeoff system such as the hybrid rocket. There are three different types of rockets: liquid rockets that use liquid propellant, solid rockets that use solid propellant, and hybrid rockets that use a solid fuel grain and liquid oxidizer. Hybrid rockets typically have lower thrust performance than solid rockets and lower specific impulse compared to liquid rockets. The motivation for this study is to improve the thrust to weight ratio of a hybrid rocket to approach that of a solid rocket and improve specific impulse to approach that of a liquid rocket, while retaining the benefits of safe handling, storage, and transportation. The scope of this study is to determine the correlation between injector swirl angle and fuel grain pitch (number of 360° revolutions per length) for optimal performance and describe this relationship with a dimensionless constant. Five different injector swirl angles will be tested with a zero-pitch fuel grain to determine the effect of injector swirl angle on thrust production. Then, one injector swirl angle will be chosen and tested with multiple fuel grains of different pitches to determine the relationship between injector swirl angle and fuel grain pitch. It is expected that thrust production will increase with injector swirl angle, and the ideal fuel grain-injector pairing will have identical pitch and swirl angle.