Enhancing Hybrid Rocket Engine Regression Rates: The Stepped Helix Design

Abstract

The novel stepped helix design consists of a series of solid fuel grain segments aligned in a rotated manner to produce a stepped helical fuel port configuration. The design increases the regression rate by facilitating augmented mixing and convective heat transfer, leveraging centrifugal forces to mitigate the wall-blowing effect that hinders heat transfer, and increasing the skin friction coefficient. Moreover, the design is easy to manufacture as it consists of identical fuel segments that form the helical fuel port solely due to their rotation relative to each other. Tests using hydrogen peroxide as the oxidizer demonstrated a regression rate increase of up to 245% compared to cylindrical reference cases. The regression rate surpasses comparable literature-reported enhancements of approximately 100% for 3D-printed helices, highlighting the synergistic effect of combining steps with helical configurations. A second iteration of the design achieved considerably fewer residuals while still maintaining between 111 and 142% regression rate increase. Through optimization, it is expected to further elevate the regression rate. The adaptable concept can be added to any existing motor.