A Comprehensive kinetic study on key reactions in monomethylhydrazine combustion and model development

Monomethylhydrazine (MMH, CH₃NHNH₂) is a widely used hypergolic fuel in aerospace propulsion due to its high reactivity and storability. However, its combustion chemistry is not completely understood, particularly at varying temperature and oxidizer conditions. This study systematically investigates the ab initio kinetics of key reactions involved in the combustion of MMH. First, a bond dissociation energy analysis was performed to identify the key species involved. Three representative reaction classes in combustion, H-atom abstraction and decomposition and isomerization, were investigated at the CCSD(T)/CBS//M06–2X/6–311++G(d,p) level of theory. The kinetic information was analysed, including potential energy surface, barrier height, reaction enthalpy, and rate constant. The computed kinetic and thermodynamic parameters were fully incorporated into a new reaction kinetic model describing MMH combustion. This model includes 188 species and 1325 reactions, incorporating the MMH decomposition model (Diévart_2020), the nitrogen chemistry (Glarborg_2018) and the C₀–C₂ (C3Mech 4.0_2025). The ignition characteristics at room temperature and combustion behavior at high temperature in the MMH/NO₂ system were investigated based on the developed model. Sensitivity and flux analyses were conducted to identify the dominant reactions governing the reactivity of the system. In addition, the thermodynamic and kinetic data reported in this study are also applicable to the development of reaction models for other C–N based fuels, such as unsymmetrical dimethylhydrazine (UDMH, (CH₃)₂NNH₂), dimethylamine (CH₃NHCH₃), and methylamine (CH₃NH₂).