Development and testing of a small scale hybrid rocket engine with a novel grain geometry

In recent years, Hybrid Rocket Propulsion has received significant attention as a candidate for space propulsion due to its safety, ability to throttle, ability to restart compared to solid rockets and low cost, simplicity and compactness compared to liquid propulsion. However, this technology also presents issues that have hampered its large scale adoption. One of the most important ones is the low and uneven regression rate of the solid fuel grain. The post-burn analyses of most fuel grains show a non-uniform regression rate along the grain length, with an increased consumption of the solid fuel at the upstream end of the motor. Various types of solutions have been studied to solve this issue, such as swirl oxidizer injection, mechanical devices embedded in the solid fuel, metallic additives, and fuel grain geometries. This thesis aims to build on the work previously carried out at the California Polytechnic State University, San Luis Obispo (USA), investigating the combined effects of a helical solid grain geometry (in order to enhance the regression rate of the fuel) with angular oxidizer injection, the goal being to induce swirl and improve the homogeneity of the burn axially along the grain, thus resulting in a more uniform regression rate along the chamber length. The first part of this work focuses on the work done to bring Cal Poly’s Hybrid Rocket Test Stand back to operational status. In the second part, we propose a new fuel grain geometry composed of a first cylindrical section followed by a helical section. The purpose of this geometry is to bring forward the swirl in the nozzle-end of the chamber, in order to obtain a more uniform regression rate between the beginning and the end of the chamber. The objectives to be measured are the greater uniformity of the regression rate along the grain; furthermore, we intend to measure the improvement in the regression rate compared to a traditional architecture (measured as a percentage increase).