Physicochemical processes of HMX propellant combustion

Abstract

The combustion processes of HMX composite propellants were studied in order to obtaina wide spectrum of burning rates. Four types of HMX composite propellants were formulated using four different types of inert binders: polyester (HTPS), polyether (HTPE), polyacetylene (HTPA), and polybutadiene (HTPB). Each has different physical and chemical properties and hydroxy terminated groups in its structure. Experimental results revealed that the burning rate of the propellants is strongly dependent on the type of binder used. When HTPE binder was replaced with HTPA, the burning rate approximately doubled. When a low-oxygen content binder (HTPB) was used, a large amount of carbonaceous material was formed on the burning surface, making the structures of the burning surface and the gas phase very heterogeneous. However, when a high-oxygen content binder (HTPE, HTPS, or HTPA) was used, these structures became homogeneous because of the formation of a molten layer of homogeneously mixed HMX/binder on the burning surface. It has been found that the combustion mode of HMX/HTPB propellants should be differentiated from that of the other three types of propellants. Thermocouple traverses in the combusition waves revealed that an increased burning rate when using HTPA binder, is due to the increased reaction rate in the first-stage reaction zone just above the burning surface. From the experimental results obtained in this study the physical and chemical processes of HMX composite propellant combustion can be deduced.