Thermal safety of solid rocket motor with complex charge structure

Abstract

This present work is focused to study thermal safety and heat transfer characteristics of large-scale solid rocket motor (SRM) with complex star-charged structure. Here, we have used three-dimensional unsteady heat transfer model coupled with a two-step global reaction mechanism of ammonium perchlorate/hydroxyl terminated polyether (AP/HTPE) propellant. Comparisons of the ignition delay time and temperature of computational results are done with experimental studies, and a reasonable match has been obtained in these comparisons. It is found that the heats transferred from the thermal environment and released from the exothermic reaction of the propellant jointly intensify the occurrence of the cook-off response of the SRM. The propellant at the bottom of the SRM can reach to a higher temperature over the time and thus the exothermic reaction is rapidly intensified with an increase of the propellant temperature, releasing more reaction heat simultaneously. The heat energy is gradually accumulated in the SRM and the propellant is eventually ignited under this high-heat environment. The ignition temperature of the SRM basically linearly increases with the AP content at 10.8% HTPE and the ignition temperature curve under different AP contents is closer to the quadratic curve at 7.8% HTPE. Also, the content of HTPE mainly has a certain effect on the ignition time that is 288 s and 283 s with its content of 7.8% and 10.8%, respectively. The heat transfer rate and the case temperature of the SRM are all increasing with an increase of environmental temperature, while the depth of the heat transfer is decreasing. Further, the ignition delay time can be expressed on environmental temperature as: ti = 2.073263exp11 × Te-2.89.