Combustion of nitrate ester plasticized polyether propellants

Abstract

Nitrate ester plasticized polyether (NEPE) is a kind of high-energy solid propellant that has both good mechanical properties and high specific impulse. However, its unique composition makes its combustion mechanism different from both double-base propellants and composite propellants. In order to study the combustion mechanism of NEPE propellants, we improved the free radical cracking model of previous research to make it capable of predicting the burning rate of NEPE propellants. To study the combustion characteristics and provide data support for the model, an experimental system was built and four kinds of NEPE propellants with different compositions and grain size distributions were tested. The results show that our modified model can reflect the combustion characteristics of NEPE propellants with an acceptable accuracy. The difference between the model and the experimental data is mainly caused by uncertain environmental factors and the ignorance of interactions between components. Both the experimental data and the results predicted by the model show that increasing the backpressure helps to increase the burning rate of NEPE propellants. Furthermore, the grain size of the oxidizer inside the NEPE propellant has a more severe impact on the burning rate but a lighter impact on the burning rate pressure exponent in comparison with the grain size of aluminum. For aluminum-free NEPE propellants, the reaction in the gas phase is dominant in the combustion process while adding aluminum into the propellant makes the solid phase dominant in the final stage. The combustion of fine aluminum particles near the burning surface generates heat feedback to the burning surface which evidently influences the surface temperature. However, the agglomeration of coarse aluminum particles has little effect on the burning surface temperature.