Unsteady Working Characteristics of Solid Rocket Motors Under Depressurization

Experiments show that, during decompression, solid rocket motors (SRMs) may undergo a downward deviation in the combustion chamber pressure or extinction. To clarify the mechanisms and laws of these phenomena, the microscale combustion of ammonium perchlorate/hydroxyl-terminated polybutadiene (AP/HTPB) propellants and the depressurization process of different SRMs are simulated with a pressure range of 1 ∼ 10.2 MPaand a pressure change rate range of −300 to − 1000 MPa∕s. The results indicate that the dynamic characteristics of the motor can be divided into three categories: monotone stability, pit-and-stability, and extinction. Under slow depressurization, the heat exchange of the system exhibits no obvious lag, unlike that observed for the pressure-change process in the combustion chamber, and monotonic stability occurs. Under fast depressurization, the solid-phase heat conduction process lags behind the change in the combustion chamber pressure, and the transient burning rate varies, resulting in pit-and-stability. A larger depressurization rate produces a greater deviation in the transient burning rate. When the depressurization process is rapid, the pyrolysis and heat conduction processes in the reaction zone on the propellant surface lag the change in combustion pressure, and the propellant is extinguished, causing extinction. A method for constructing the SRM relaxation coefficient distribution based on its design and propellant parameters is established. By determining the position of characteristic points within the relaxation coefficient distribution, the dynamic operating characteristics of the SRM under depressurization are revealed.