Heat transfer process and reaction mechanism of AP/HTPB propellant under transient high temperature

Abstract

For the safe use of solid rocket motors, it is crucial to investigate the thermal effect of AP/HTPB propellants. Transient high temperature may cause AP/HTPB propellants to burn or explode, resulting in serious damage. The fundamental equations that describe the thermal effect of AP/HTPB propellants are the heat conduction differential equation and Arrhenius law. In this paper, the thermal safety of AP/HTPB at transient high temperature is obtained by solving the heat conduction differential equation. The results show that the chemical source term S(T) is the main control factor of thermal runaway. When the action duration of the external high-temperature is short (ms-s magnitude), the first explosion occurs closest to the high-temperature source. When the action duration of the external high-temperature action is long (min-h magnitude), the first explosion occurs inside the propellant. The higher the high-temperature intensity of external action, the shorter the explosion delay time, but the explosion temperature does not change accordingly. The critical temperature of thermal runaway is 458 K under the condition of no shell and a high-temperature action duration of 2 h. At high-temperature intensities of 458 K, 459 K, and 500 K, the propellant explosion temperatures are 533 K, 539 K, and 540 K, and the explosion delay time is 1592s, 1102s, and 160 s, respectively. The critical duration of thermal runaway is 430 ms, 650 ms, 1350 ms, and 9820 ms, and the stable explosion delay time is 450 ms, 680 ms, 1400 ms, and 9920 ms, respectively, under the conditions of 2000 K, 1500 K, 1000 K, and 600 K without the shell. The propellant explosion temperature remains constant as the shell thickness grows while the explosion delay time gradually increases. When the propellant is thick enough, the temperature distribution of the system remains constant. The results of this study may be useful as a guide for assessing the thermal safety of AP/HTPB propellant.