Effect of AP and AN on the combustion and injection performance of Al-H2O gelled propellant

Aluminum-water propellants (Al-H₂O propellants), representing a novel class of solid propellants, demonstrate the merits of cost efficiency and reduced feature signal characteristics. However, the conventional formulations of Al-H₂O propellants are hampered by the generation of substantial condensed residues. In our investigation, we explored the incorporation of oxidizers into the Al-H₂O propellant grain, aiming to enhance combustion and injection performance. Employing a multifaceted experimental approach, we conducted thermal gravimetric analysis, laser ignition experiments, and ignition tests within a lab-scale solid rocket motor (SRM) firing to systematically examine the effects of varying content of ammonium perchlorate (AP) and ammonium nitrate (AN) on the combustion and injection performance of Al-H₂O propellants. Our findings indicated that integrating AP and AN at a mass fraction of 3 % each notably curtailed ignition delay time by approximately 67 % and 90 %, respectively, and concurrently decreased burning rates by approximately 50 % and 58 %. Significantly, it has been observed that a composition incorporating a 5 % mass fraction of AP enhances the combustion efficiency of the Al-H₂O propellant system by approximately 2 %. Conversely, the integration of a 5 % mass fraction of AN into the same propellant matrix results in an augmentation of the injection efficiency by an estimated 47 %. Empirical evidence validating the augmentative impacts of AP and AN on the performance of Al-H₂O propellants has been substantiated through a series of motor hot firing experiments. Furthermore, the combustion behavior of Al-H₂O propellants has been elucidated through an analysis of the combustion physical mechanism of Al particles. The thermal decomposition of AP yields a substantial volume of oxidizing gases, which effectively accelerates the combustion rate of the Al particles, subsequently leading to an enhancement in the overall combustion efficiency of the propellant. Conversely, the decomposition of AN results in an increased production of nitrogen gas, thereby augmenting the velocity of gas flow and, consequently, elevating the injection efficiency of the propellant. This finding holds promise for guiding the developmental trajectory of Al-H₂O propellants and refining the design parameters of propulsion systems.