Modeling the combustion chemistry of typical nitramine monopropellants: A critical review

Abstract

Solid propellant is the power source of various types of solid engines, such as missiles and space vehicles, and its combustion performance directly affects the combat effectiveness and survivability of missile weapons. The chemical reaction kinetics of solid propellant is useful for understanding the combustion chemistry of real energetic materials, guiding the efficient and successful design of next-generation propellants, and warning of the risks during practical processing and application. In this paper, the chemical reaction kinetics of typical nitramine monopropellants, i.e., cyclotrimethylenetrinitramine (RDX), cyclotetrimethylenetetranitramine (HMX), and hexanitrohexaazaisowurtzitane (CL-20), is reviewed, including the thermal decomposition of nitramines in the condensed and gas phase, the reaction mechanism of small molecules in the gas phase, and the model performance of current nitramine propellants. In terms of the primary decomposition mechanism of each nitramine monopropellant, the formation pathways of fuel-specific intermediates and the distribution of major volatiles are discussed based on the comparison of theoretical calculations and experimental measurements. In terms of the gas-phase reaction mechanism, recent nitrogen-involved fundamental reaction mechanisms are reviewed, and the CN interaction mechanisms in propellant systems are also discussed. In the past two decades, modeling methods for solid propellants have made remarkable progress, especially in the development of condensed-phase reaction kinetics, which have evolved from the previous global reaction mechanism of several steps to the detailed reaction mechanism based on high-level quantum chemistry methods. However, at present, the initial decomposition mechanism of solid propellant cannot accurately predict the fuel-specific intermediates measured in the experiments, and there is an urgent need for the development of combustion models based on ab initio principles with acceptable predictability.