Study on combustion termination of solid propellants by rapid depressurization

Abstract

AN experimental investigation of the extinction behavior of solid composite propellants (PBAN + AP) by rapid depressurization is made. An analytic procedure by an adiabatic (or isentropic process) and Summerfield's burning rate law is taken to predict pressure decay. The vents' opening rate is assumed to be a parabolic function of time; also, a model of adiabatic-is entropic combined process is proposed for improving the predictions. Contents Ciepluch concluded that there was a minimum depressurization rate (dP/dOc required to extinguish combustion, * that many solid propellant compositions might be susceptible to the reignition phenomenon, and that the residual chamber gas and the residual heat in the propellant surface were the primary sources of ignition energy.2 Jensen and Brown3 found that the exhaust pressure level could influence extinction and reignition behavior. Experimental investigation of this study is achieved by using a test motor shown schematically in Fig. 1. As shown, two additional vents on the head of the motor were blocked up with vent covers that were held in position with two U-clamp bends and two explosive bolts. The motor was depressurized rapidly by initiating the explosive bolts and opening the vents. A pressure transducer and a high-speed camera were used to record the pressure variation and extinction phenomena, respectively. The results are listed in Table 1. It is found that the combustion of PBAN propellants was extinguished temporarily by opening suitable venting ratio ports on the motor head, but that reignition occurred because of residual heat feeding back to the propellant grain under the test environment of 1 atm. Furthermore, the reignition could be delayed by inserting vulcanized fiber between the freestanding grain and the motor case (with motors 2 and 4) because of the effects of reducing residual heat transfer from the motor case and hot gases. In this investigation either an isentropic or an adiabatic is assumed, and Summerfield's burning rate law is used to predict pressure decay. Besides, the venting ratio is assumed as a parabolic function of time 4 during the period of delayed time td before full opening of the vents. The main assumption of isentropic pressure decay is that the extinction occurs immediately upon opening of the vents without time delay. For the case of adiabatic pressure decay,