Investigation of Al-Li alloy particles for performance enhancement in solid rocket motors

Al-Li alloy particles, which offer advantages such as a shorter ignition delay time, have been recognized as promising metallic fuels for replacing conventional aluminum powder to enhance the performance of solid rocket motors. In this study, experimental and theoretical investigations were conducted on the energy characteristics of solid rocket motors fueled with Al-Li alloy particles. Initially, the agglomerate size near the propellant burning surface was experimentally determined to establish the initial diameter for the discrete phase model. The characteristic velocity and specific impulse were obtained through ground testing of solid rocket motors. Subsequently, a two-phase flow model was developed within the Euler-Lagrangian framework, incorporating the combustion and secondary breakup processes of Al-Li alloy particles. The simulated characteristic velocity and specific impulse exhibited close agreement with experimental values. Numerical results indicate that increasing the lithium content in the alloy particles improves the characteristic velocity. This enhancement is attributed to a reduction in the average molecular weight of the combustion products and an increase in chamber temperature, with both factors contributing equally. Furthermore, higher lithium content reduces the size of the oxide caps formed after particle combustion and decreases the mass flow rate of condensed combustion products, thereby significantly mitigating two-phase flow losses. However, due to non-uniform fluid distribution caused by two-phase flow within the nozzle, the predicted non-axial loss coefficient exceeds the theoretical value and shows negligible dependence on lithium content. Thus, increasing the lithium content primarily improves the actual specific impulse by enhancing the propellant combustion efficiency and reducing two-phase flow losses. Finally, an empirical correlation was established to predict the actual specific impulse of solid rocket motors employing Al-Li alloy particles.