Swirl Injection of Gaseous Oxygen in a Lab-Scale Paraffin Hybrid Rocket Motor

Research has shown that oxidizer swirl injection and liquefiable fuels, such as paraffin wax, can increase regression rates in hybrid rockets. However, there are few studies published on motors that use both these strategies simultaneously. This paper presents an exhaustive experimental investigation on the performance of a lab-scale hybrid rocket motor using paraffin wax and gaseous oxygen under a number of different conditions, including five different oxidizer injectors with varying levels of swirl. Prechamber length, fuel grain length, burn duration, oxidizer mass flow rate, and fuel grain geometry were modified from a baseline, and the influence on fuel regression and thrust oscillations was evaluated. Swirl injection increased regression rates up to 2.4 times that of the baseline axial injection configuration, while providing smoother operating conditions. The results show that thrust density of a hybrid rocket can be increased simultaneously by the use of a liquefying fuel and swirl injection. The results obtained also provide a unique experimental observation of the influence of several motor parameters on its performance, revealing that prechamber length and the angle of an entry slope on the grain do not contribute significantly to the performance or stability of the motor with swirl injection.