Small-Scale Hybrid Rocket Test Stand & Characterization of Swirl Injectors

A small-scale motor and test stand were designed and developed with specific emphasis on characterizing swirl flow injection angles. The motor is designed for simple integration and setup, such that both the forward-end enclosure and end cap can be easily removed for rapid integration of components during testing. While examining injectors and their potential it is thought ideal to obtain the highest regression rates and overall motor performance. The oxidizer and fuel are nitrous oxide and hydroxyl-terminated polybutadiene, respectively, due to previous experience and simplicity. The injector designs, selected for the same reasons, are designed such that they vary only in the swirl angle with tested Swirl Flow numbers of S= 0, 0.18, 0.39, 0.6 and 1.15. The system was limited in oxidizer mass flow rate so additional tests are required at higher mass fluxes for a reasonable fit for the regression rate exponent. Key results include an increase in 60 degree swirl flow injector regression rate as high as 1.63 times the regression rates of zero degree swirl flow injectors for similar oxidizer mass flux conditions. The results also show a nearly uniform regression rate along the grain length for the highest swirl flow number injector tests. A sensitivity analysis demonstrates that oxidizer mass flux and swirl flow number are the leading variables in the regression rate of this hybrid rocket motor. This is evidence that an alternate definition of oxidizer mass flux should be investigated to augment the fundamental hybrid rocket motor regression rate equation when using swirl flow injection.