Effect of Aluminum Content on the Combustion Performance of HTPB/AP/Al Propellants under High Combustion Pressure

Combustion mechanisms of propellants under high combustion pressure are extremely important for the development of high-pressure solid rocket motors. The combustion characteristics of three HTPB propellants prepared with an aluminum content of 1%, 10%, and 18% were evaluated in this study by analyzing the extinguished propellant surface, the combustion flame, and the temperature profile in the combustion pressure range of 12-30 MPa. The results showed that the burning surface temperature of the three propellants increased from 425 to 535 and to 643 ℃ as the aluminum content was increased from 1% to 18%, resulting in a faster thermal decomposition rate of the binder than the thermal decomposition rate of the AP particles. Consequently, the morphology of the extinguished propellant surface evolved from concave into convex, and the higher the aluminum content, the more obvious became the convex morphology. The combustion flame height of the three propellants showed a downward trend when the combustion pressure was increased from 12 to 18 MPa, enhancing the heat feedback to the burning surface. The burning surface temperature of the three samples increased by 75, 105 and 189 ℃, respectively, with the increase in combustion pressure, resulting in a more distinct degree of concave and convex morphology of the extinguished propellant surface. In addition, this demonstrated that the local heat and mass transfer might play a dominant role under high pressures.