Analysis of the aluminum reaction efficiency in a hydro-reactive fuel propellant used for a water ramjet

A high-pressure combustor and a metal/steam reactor are used to simulate the two-stage combustion of hydro-reactive propellants used for a water ramjet. Raw metal powders added to the propellants are the aluminum power, magnesium powder, 50/50 aluminum-magnesium alloy (AM), and ball-milled 50/50 aluminum-magnesium alloy (b-AM), which are characterized by using scanning electron microscopy (SEM), x-ray diffraction (XRD), and simultaneous thermogravimetric analysis (TGA). The efficiencies of the Al reaction in the raw metal in heated steam and in the propellants during the two-stage combustion are calculated. The results indicate that both Mg and Al in the alloys, whether b-AM or AM, can react completely in air when heated up to 950 C. The XRD patterns for the combustion products of the AM and b-AM alloys in heated steam contain magnesium oxide MgO, spinel Al₂MgO₄, and Al diffraction peaks. The Al reaction efficiencies of the AM and b-AM alloy powders in heated steam are much higher than that of the Al powders. The hydroxyl-terminated polybutadiene (HTPB)-ammonium perchlorate (AP)-(b-AM)-Mg and HTPB-AP-AM-Mg propellant systems exhibit good performance in terms of the Al reaction efficiency, which are better than that of the HTPB-AP-Al-Mg and HTPB-AP-Al systems.