Study on the influence of acceleration on the characteristics of condensed combustion products in solid rocket motors

The characteristics of condensed combustion products (CCPs) under acceleration are vital to the operational performance and thermal protection safety of solid rocket motors (SRMs). Nevertheless, systematic and comprehensive studies regarding the dynamic evolution and deposition of CCPs, aluminum combustion efficiency, and performance of SRMs under acceleration are still lacking, restricting the further optimization of SRM thermal protection and performance. To address this issue, a dedicated SRM is designed to collect CCPs at both the propellant burning surface and the SRM rear cavity. Firing tests under different accelerations are carried out to acquire CCPs and SRM performance data. The particle size distribution, microscopic morphology, and component characteristics of CCPs are quantitatively analyzed. Combined with internal ballistic variations and nozzle plume features, the coupled influence mechanism of acceleration on CCP evolution and SRM performance is clarified. The results show that axial acceleration reduces the residence time of aluminum droplets in the combustion chamber, lowering aluminum combustion efficiency and increasing CCP deposition at the SRM rear section. The heat loss from unburnt aluminum consequently degrades SRM performance. With axial acceleration increasing from 0 g to 20 g, the SRM pressure build-up rate, overall performance, and aluminum combustion efficiency decline by 60.2%, 8.03%, and 17.97%, respectively. Unburned residual aluminum undergoes secondary combustion in the plume and enhances the plume signature. Acceleration acting outward normal to the propellant burning surface inhibits agglomeration of aluminum droplets and reduces the particle size of CCPs. Oxidizer-deficient environments in deposits induce Al₂O₃-C-N₂ reactions to generate Al₂OC and AlN, making the aluminum combustion efficiency derived from condensed deposits lower than the actual efficiency in the combustion chamber.