The burning rate of a solid propellant is a fundamental characteristic, which is measured for every propellant composition that is aimed to be used in a rocket motor. The burning rate measuring procedure in the lab requires mixing of all propellant ingredients, casting of the material into moulds, hot curing of the material, extracting strand samples and burning of many samples at various pressures. This procedure is long and requires significant resources, thus the motivation for developing a theoretical model, able to predict the burning rate of a given composition is obvious.
A solid propellant is a mixture of a polymeric binder that contains a hydrocarbon fuel, plasticizer, surface agents, cross linking agents etc. together with crystalline oxidizer particles in two or three size groups. The combustion of such a mixture is very complex and is affected by several combustion mechanisms and by different type of flames. The combustion mechanism depends on the pressure, the amount of oxidizer particles and their size distribution. The heat transfer from the flame plane to the propellant surface determines the propellant burning rate.
The well-known, BDP model, developed by three investigators, Beckstead, Derr and Price, is an analytical model that presents a set of equations with a closed solution that provides the burning rate of a given composition as a function on pressure.
In the frame of the present work, the BDP model was implemented in a computer code developed in Rafael. A comparison of the prediction to experimental data reported in literature and self preformed experimental data was conducted. In the second stage, a model correction was proposed in order to improve the prediction for low burning rate propellants.
In the experimental part of the research 14 “reduced smoke” propellant compositions were tested and about 100 experiments were conducted at various pressures. The revised model that was developed in the present study shows a very good agreement with the tested propellants.