A model of composite solid-propellant combustion based on multiple flames

TLDR

The model represents AP composite propellant combustion as a multi‑zone flame surrounding oxidizer crystals, with statistical coupling to the binder matrix, simple global gas‑phase kinetics, Arrhenius surface decomposition, and oxidizer decomposition treated as the overall controlling step. Model predictions of surface temperature, oxidizer concentration effects, and exothermic surface reactions agree with experimental trends, though particle‑size sensitivity is over‑predicted, and the calculations confirm that AP partially decomposes exothermically in the thin surface melt.

Abstract

A model describing the combustion of AP composite propellants has been developed. The model is based on a flame structure surrounding individual oxidizer crystals; the relationship between crystals and the binder matrix being evaluated statistically. Three separate flame zones are considered: 1) a primary flame between the decomposition products of the binder and the oxidizer, 2) a premixed oxidizer flame, and 3) a final diffusion flame between the products of the other two flames. Simple global kinetics are assumed for gas-phase reactions, and the surface decomposition of the propellant ingredients is assumed to be adequately described by simple Arrhenius expressions. The oxidizer decomposition is taken as being the over-all controlling factor in the combustion process. The results obtained show that the calculated surface temperature and the effect of oxidizer concentration predicted by the model are in agreement with observed experimental trends. The predicted effect of particle size is somewhat greater than observed experimentally while the temperature sensitivity is in excellent agreement with experimental data. The results of the calculations indicate a relatively strong exothermic reaction taking place at the propellant surface. Apparently the ammonium perchlorate (AP) partially decomposes exothermically in the thin surface melt previously reported in AP deflagration studies.