Improving the model for determining the composition of gunpowder gases during thermal destruction of gunpowder in a limited volume space

The object of this study is a model of the process of formation of products of thermal destruction of nitrocellulose powder at different values of pressure of the mixture of powder gases. The work is aimed at eliminating the uncertainty in the list of powder combustion products. In many cases, the formation of condensed carbon during the shot is not taken into account, which does not correspond to the real process. The process of formation of powder combustion products has been studied both under experimental conditions at a pressure of several MPa, and under shot conditions at a pressure of ~300 MPa and more. The proposed model makes it possible to explain the cause and conditions of condensed carbon formation. The possibility of formation of up to 10 % of condensed carbon from the initial mass of powder during the shot has been shown. An improved model was built using the molar composition of the combustion products. The calculation of the specific volumes of gaseous reaction products with a change in the pressure of the gas mixture was carried out taking into account the change in their compressibility coefficient based on the Peng-Robinson equation. Within the limits of pressure values change during the shot process, the possibility of changing the equilibrium constant values in the range from ~40 % to twofold has been shown. The formation of condensed carbon is explained by the reaction of carbon monoxide disproportionation. The range of values of thermodynamic parameters of powder gases that ensure the possibility of this reaction was identified. The proposed model could be used in the experimental determination of the composition and energy characteristics of a powder sample in the field based on the library method. Given the identified powder composition, the problem of internal ballistics could be solved for the prompt determination of shot parameters