Effects of low pressure and low temperature on aluminum agglomeration, gas phase flow velocity, and condensed combustion products in solid propellants

In this study, the agglomeration behavior, gaseous combustion products flow velocity and characteristics of condensed combustion products (CCPs) from a HTPB-based solid propellant were systematically investigated under low-pressure and low-temperature conditions. Furthermore, the underlying mechanisms of these environmental effects were discussed. High-speed microscopic imaging was employed to observe and quantify the agglomeration behavior near the burning surface. Meanwhile, the gaseous combustion product stream velocity in this region was analyzed using both kinetic modeling and theoretical calculations. Experimental results show that when pressure decreases from 1 atm to 0.5 atm, the agglomerate occurrence frequency drops by 90.2 %, the average particle size increases by 14.4 %, and the gaseous product velocity rises by 52.1 %. When reducing the ambient temperature from 20 °C to −40 °C leads to an 18.1 % decrease in agglomerate frequency and a 6.5 % reduction in average particle size, while its effect on gaseous velocity remains inconclusive. Characterization of CCPs reveals that both low pressure and low temperature significantly alter the particle size distribution and reduce the combustion efficiency of solid propellants. Within the experimental conditions of this study (0.3 atm to 1 atm, −40 °C to 20 °C), the impact of pressure changes is greater than that of temperature.