Steady-State Combustion Mechanisms of Ammonium Perchlorate Composite Propellants

Abstract

The flame structures emanating from a mixture of ammonium perchlorate (AP) and hydroxy-terminatedpolybutadiene (HTPB) have been calculated over a range of pressures and AP particle sizes using high-fidelity simulations. The calculated AP composite propellant flame structure consists of three premixed flames (AP monopropellant flame, homogenized-binder flame, and primary flame) and a diffusion flame. The variations in this flame structure, based on pressure and particle size, account for AP's unique combustion properties. As pressure is increased, the three premixed flames draw closer to the surface, increasing the propellant burning rate. However, the diffusion flame is forced farther into the gas phase, decreasing the propellant burning rate. This dichotomy creates large variations in how AP composite propellants burn at different pressures. Three regions of combustion have been calculated for AP composite propellants: the AP monopropellant limit, the diffusion flame region, and the premixed limit. The premixed limit represents the maximum burning rate, and the AP monopropellant limit represents the minimum burning rate. AP particle size and pressure dictate the region of combustion, as these parameters greatly affect the flame structure. A thorough explanation of AP's pressure and particle-size effects with regard to a propellant's burning rate is presented. Propellant burning rates and premixed cutoff diameters are predicted for an AP/HTPB system. The importance of correctly representing the homogenized binder in AP/HTPB propellant combustion simulations is also discussed.

Slow-Burn Ammonium Perchlorate Propellants with Oxamide: Burn Rate Model, Testing, and Applications

“…Although the effects of pressure and AP particle size on burn rate have been throughly studied (e.g. [7][8][9]), the effect of oxamide has received less attention, as slow-burn propellants are not widely used. Regarding the physical and chemical mechanisms of burn rate suppression, Trache et al [10,11] have provided some insight by investigating the thermal decomposition of oxamide-doped AP propellants and of pure oxamide.…”

“…Two techniques were used to create slow-burning AP composite propellants: large AP particles and a burn rate suppressant, oxamide. First, the propellant burn rate was decreased by increasing the AP particle size; however this effect saturates for particles larger than about 400 µm [9,15], and using large AP particles alone does not make the propellant burn rate slow enough for this application.…”