Burning-Rate Predictor for Multi-Ingredient Propellants: Nitrate-Ester Propellants

Abstract

The theoretical capability to predict the burning rate of real propellants from their ingredients would be an invaluable aid to formulating new propellants. Despite progress over the last decade on a very few simple ingredients, such as cyclotrimethylenetrinitramine (RDX), and a few simple binary mixtures, no general capability of this sort exists today. This shortcoming is not due to insufficient computational resources, but to a lack of understanding of fundamental combustion mechanisms in the condensed phase and surface/gas interface for typical propellant ingredients and their mixtures. This difficult problem is likely to remain intractable for some time to come. It is demonstrated that our previously published semi-empirical formalism for single ingredients can be successfully extended to treat multi-ingredient propellants. In particular, the study is confined to nitrate‐ester propellants (using M10, M2, M9, and JA2 as examples). However, the method should also be applicable to other classes of homogeneous propellants and even composite propellants where mixing of ingredients in a surface melt layer or sufficiently small particle sizes remove the multidimensional character. The method treats the gas-phase processes on the level of elementary reactions and multicomponent transport. A semi-empirical pyrolysis law coupled with informed estimates of the decomposition products of the condensed phase enables us to finesse the absence of knowledge of the detailed processes occurring in the condensed phase and at the burning surface. Results of a computer code, CYCLOPS, based on this approach, show that both the burning rate and flame structure are well predicted for a series of four U.S. Army gun propellants.