Unveiling the Microexplosion-Driven Combustion Enhancement in Additively Manufactured Al–Li/HTPB Propellant Matrices

Aluminum (Al) powder has been the conventional fuel in solid propellants; however, its combustion products frequently undergo agglomeration during combustion, causing significant energy losses. In this study, additive manufacturing technology was applied to fabricate Al–Li/HTPB solid propellants to gain more energy release. The SEM results demonstrate a uniform component distribution without defects. Compared with the Al/HTPB solid propellant, the friction load is increased by over 36 N and the activation energy of the thermal decomposition is reduced by 38.9 kJ/mol, proving a more stable mechanical safety and high thermal reactivity. The open-air combustion test found that the combustion process of the Al–Li/HTPB solid propellant is accompanied by an intense microexplosion phenomenon. Moreover, the heat release of propellants with Al–Li powders can increase by over 246 J/g, and the combustion temperature was 128.7 °C higher than propellants with Al powders. The analysis of combustion products confirms the complete combustion of Al–Li powders, which greatly contributes to the energy release. Furthermore, molecular dynamics (MD) simulations are employed to preliminarily investigate the microexplosion phenomenon. Within the temperature range of 300–1000 K, the thermal conductivity of the Al–Li alloy decreased from 3.21 to 1.21 W/(mK), while for pure Al it decreased from 8.88 to 1.73 W/(mK). A substantial decrease in interfacial thermal conductivity is observed for Al–Li/AP (0.3900 W/m2K) relative to Al/AP (0.6332 W/m2K). Thus, the powder inherent thermal conductivity contributed to the microexplosion of propellants containing Al–Li powders. The study revealed that Al–Li alloy powder can be a good candidate fuel in the additive-manufactured propellants.