Sensitivity analysis of kinetic, thermodynamic, and transport parameters in HMX (1,3,5,7- tetranitro-1,3,5,7-tetrazocane) combustion modeling

Chemical kinetic mechanisms are crucial for modeling the combustion processes of solid propellants, but the specific impacts of these mechanism’s parameters on combustion have not been fully assessed. This study conducted a comprehensive sensitivity analysis on kinetics, thermodynamics, and transport parameters affecting solid propellant mechanisms, exemplified with HMX as a case study. A onedimensional steady-state numerical model incorporating gas and liquid phase mechanisms of HMX was developed and validated against experimental data. This model enables a thorough sensitivity analysis to evaluate the influence of various parameters, including the reaction constant (k) of each elementary reaction, enthalpy of formation (hf), entropy (s), heat capacity (cp), collision diameter (σ), and potential well-depth (ε) of each species, on key combustion characteristics over a wide range of pressure. The analysis revealed that gas kinetics predominantly govern the HMX combustion compared to the liquid kinetics, particularly at high pressures. Notably, the decomposition reactions of H2CNNO2 and N2O in the gas phase were identified as highly sensitive reactions that control the r and the pressure exponent of HMX. By calculating the normalized sensitivity coefficients of all parameters, the cp values of small gaseous molecules were found to be the most significant factors affecting combustion, indicating a role played by the thermodynamic properties of small species. This research could enhance our understanding of HMX combustion mechanisms and underscore critical areas for future development and refinement of detailed kinetic mechanisms of solid propellants.