Development and Verification of a Lab-Scale Green Propellant Hybrid Motor System

Hybrid rocket propulsion offers the potential to combine advantages of both solid and liquid propellant systems, but low regression rates hinder their practicality. The suggested use of hydroxylammonium nitrate (HAN) based propellants in hybrids offers the potential for developing high impulse motors with low development and production costs. In this paper, I present the development of a small-scale system used to measure the regression rate of a hybrid motor. The system can accommodate fuel grains 5 cm long with an outer diameter of 6 cm and can implement the various decomposition gases needed for HAN. The motor firings of hydroxyl terminated polybutadiene (HTPB) burning with gaseous oxygen at oxidizer mass fluxes (0.2 – 0.6 g/cm2-s) agree well with literature. The preliminary motor firings with the HAN decomposition gases proved challenging due to the high steam concentration.