Investigating Dimensional Effects on Predicting Burning Rates of Heterogeneous Solid Propellants

Abstract

The combustion of a randomly packed, heterogeneous propellant consisting of ammonium perchlorate and hydroxyl-terminated polybutadiene is investigated in a two-dimensional and three-dimensional numerical model to better understand the dimensional effects on the propellant burning rate. A ammonium perchlorate particle is set in a premixed hydroxyl-terminated polybutadiene binder and investigated using a two-dimensional model with finite-rate chemistry and detailed transport properties. The results from the detailed model are compared to two-dimensional and three-dimensional burning-rate codes with reduced chemistry. The gas-phase combustion chemistry is modeled using a reduced four-step mechanism developed from a detailed microscale model of ammonium perchlorate/hydroxyl-terminated polybutadiene combustion. Simple configurations of a single ammonium perchlorate particle and sandwich propellants at varying pressures are compared to determine leading-order effects of two-dimensional and three-dimensional approaches. The reduced chemistry models are then applied to real-world propellants for which a random packing algorithm is used to construct the ammonium perchlorate/hydroxyl-terminated polybutadiene propellant in a periodic cube for a given size distribution of spherical ammonium perchlorate particles and mass ratio of the oxidizer and binder. The decomposition of the ammonium perchlorate and hydroxyl-terminated polybutadiene on the surface is determined at discrete locations and is used to determine the average burning rate over a period of time. This approach combines a more detailed description of the gas-phase combustion processes, the condensed-phase morphology, and physics in a time-dependent simulation in hopes of developing a more predictive model of solid propellant combustion.