Condensed Combustion Products Characteristics of HTPB/AP/Al Propellants under Solid Rocket Motor Conditions

Abstract

Condensed combustion products (CCPs) generated during the combustion of aluminized propellants can reflect invaluable information about the combustion mechanisms of propellants. CCPs of hydroxyl-terminated polybutadiene/ammonium perchlorate/aluminum (HTPB/AP/Al) propellants were collected using an experimental apparatus capable of controlling pressure fluctuations within 0.3 MPa, and their microscopic morphologies, particle size distributions, and chemical compositions were characterized using a scanning electron microscope (SEM), laser particle size analyzer, energy disperse spectroscopy (EDS), X-ray diffraction (XRD) and complexometric titration. The results showed that the size of CCPs presented a bimodal distribution, with modes at ~5 µm and ~100 µm; particles less than 2 µm were spherical, with smooth surfaces. The main components of CCPs were C, AlN, AlCl3, Al2O3, Fe2O3 and Al, with Al2O3 being the most abundant. The combustion efficiency of aluminum increased by 3.27% when the size of virgin aluminum particles decreased from 23 µm to 13 µm, but the content of catocene (a burning-rate catalyst) and fine AP (1 µm) had little effect on combustion efficiency. Higher combustion efficiencies and smaller agglomeration sizes can be achieved at higher pressures, due to the positive correlation between pressure and the driving forces for aluminum particles exciting the burning surface.

Enhancing the Ignition and Combustion Performances of Solid Propellants Incorporating Al Particles Inside Oxidizers

“…According to the size of CCPs, Al@AP favored reducing the agglomeration in SP13 and SP14, even better than AP@Al-1. This may be attributed to the smaller size of AP . The decrease of Al agglomeration using Al@oxidizer was similar to those of coating materials such as stearic acid and Viton, but the mechanism can be very different.…”

“…This may be attributed to the smaller size of AP. 44 The decrease of Al agglomeration using Al@oxidizer was similar to those of coating materials such as stearic acid and Viton, 45 but the mechanism can be very different. According to previous works, the intimate contact between Al and oxidizers offers enhanced reaction efficiency of Al particles, 27,31 leading to less accumulation and aggregation during the combustion process.…”

Energy-Intensive Materials with Mechanically Activated Components

“…This elevated heat release during metal oxidation increases the flame temperature, thereby boosting the specific impulse value in aluminized fuel by approximately 10%. Additionally, there is another crucial characteristic to consider: the unstable combustion of aluminum and aluminum-based systems, which becomes significant when employing aluminum in condensed systems [32,33]. The inclusion of highly dispersed aluminum can enhance the propellant capabilities of compositions when compared to pure explosives.…”

Numerical Investigation on the Effect of Ammonium Perchlorate Content and Position on the Combustion Characteristics of an Ammonium Perchlorate/Hydroxyl-Terminated Polybutadiene Propellant

“…As the most widely used propellant in the world [5][6][7][8], the AP/HTPB composite propellant has been studied by many researchers, and various steady-state combustion models based on experimental phenomena have been proposed to help understand the combustion processes and phenomena [9][10][11][12]. The Beckstead-Derr-Price (BDP) model is the most classic one, which describes the heating and combustion of AP and HTPB, including endothermic decomposition, condensed-phase surface reaction, solid-phase exothermic and gas-phase reaction, as well as the component transport process [13].…”