Regression Rate Model Predictions of an Axial-Injection End-Burning Hybrid Motor

Abstract

This paper investigated the predictions of the axial-injection end-burning hybrid rocket motor regression rate model developed by Hitt and Frederick. Because axial-injection end-burning hybrid rocket motors follow a regression rate trend based on chamber pressure (like a solid rocket motor) instead of oxidizer mass flux (like a classical hybrid), it was expected that axial-injection end-burning hybrids would have additional regression rate trends similar to what is observed in solid rocket motors. As such, model predictions based on variations in chamber pressure, fuel grain temperature, oxidizer mass flow rate, and oxidizer pore size were investigated. The results of the modeling predicted that increases in the grain temperature increased the regression rate; but, increases in the oxidizer mass flow rate would decrease the regression rate. Increasing the oxidizer pore size was predicted to decrease the regression rate, with the effect increasing with chamber pressure as the flame became more diffusion limited. These results provide a better understanding of the axial-injection end-burning hybrid design, and thus better insight into where to focus further research.