Regression Rate Design Tailoring Through Vortex Injection in Hybrid Rocket Motors

In the last few decades, vortex injection has been proposed as a possible solution to main hybrid rocket motor drawbacks. The aim of this work is to understand the effects of the swirl intensity and the postchamber length on a 300 N hybrid rocket motor by using H2O2 as the oxidizer and high-density polyethylene as the solid fuel with a classical cylindrical port grain. Three different injection plates have been designed in order to obtain three different geometrical swirl numbers; at the same time, three different postchamber lengths have been used. The numerical and experimental investigations have proved that swirl injection allows a good motor efficiency without the need for a long postchamber. From the analysis of fuel consumption data, a linear relation between the grain surface regression rate and the intensity of the swirling flow given by vortex injection has been obtained. This information could be used in future design phases to tailor the fuel regression in order to achieve the best packaging of a hybrid rocket motor for a desired mission profile.