Abstract
Hybrid rocket engines are studied internationally because they provide many benefits. However, hybrid rocket engines are rarely put into practical use because of their low regression rate. Earlier research efforts have been aimed at improving the regression rate using paraffin or microcrystalline wax (WAX) and adding metal powder to solid fuel. For hybrid rocket solid fuels, aluminum (Al) powder is used as a metallic fuel. Nevertheless, effects of adding Al powder have not been confirmed sufficiently because Al powder is reportedly difficult to ignite in the combustion chamber of a hybrid rocket engine. Magnesium (Mg) powder ignites more easily. This study specifically assessed addition of microscale magnalium (Mg-Al) powder particles because Mg-Al can overcome these and other shortcomings. Reportedly, Mg-Al powder has good combustion completeness in solid propellant1). This study used combustion experiments to elucidate effects of Mg-Al powder addition to WAX. Combustion experiments using a small hybrid rocket engine demonstrated that 20 mass% Mg-Al powder in WAX produces an 18.7 % increased regression rate over that of WAX alone, which is greater than adding Mg or Al. These results suggest that high combustion heat of Mg-Al powder promotes WAX combustion. Adding Mg-Al powder raises the regression rate. Additionally, residue remaining in the aft chamber after combustion was analyzed using XRD. The results of these two analyses suggest that the Mg-Al powder was ignited and burned in the aft chamber. A small combustion chamber can be used because Mg-Al powder has high density and excellent completeness of combustion. Results demonstrate that Mg-Al powder is suitable for addition to solid fuel of small hybrid rocket engines.
