A Theoretical Kinetic Study of Nitrocyclohexane Combustion: Thermal Decomposition Behavior and H-Atom Abstraction.

Nitrocyclohexane (NCH) is regarded as a highly promising energetic liquid fuel and additive for pulse detonation engines (PDEs) due to its excellent ignition performance and rapid energy release characteristics. Developing a detailed kinetic model for NCH is crucial for understanding its combustion characteristics and accurately predicting its behavior under actual operating conditions. In this study, reactive molecular dynamics (RMD) simulations were performed employing the force field and the canonical (NVT) ensemble to investigate the temperature-dependent kinetic behavior of NCH. The results indicate that the initial decomposition of NCH is primarily driven by C-N bond rupture, followed by C-H bond cleavage, H atom abstraction, and other reactions, with H-abstraction playing a more significant role at lower temperatures. Subsequently, a systematic investigation of H-abstraction at seven sites in NCH involving six small species (Ḣ, ȮH, ĊN, HȮ, NO, and O) was conducted at the QCISD(T)/cc-pVXZ(X = D,T)//MP2/cc-pVXZ (X = D,T,Q)//M06-2X/6-311++G(d,p) level of theory. The calculations reveal that there are minimal differences in reactivity between axial and equatorial H-abstraction, which proceed as parallel reaction channels. Compared to H-abstraction at nitro-substituted, meta, and para positions on the NCH ring, ortho H-abstraction reactions exhibit relatively lower rate coefficients. The obtained kinetic parameters in Arrhenius form and thermodynamic data in NASA polynomial format, covering a wide temperature range (298.15-2000 K), can be directly utilized for the development of the NCH kinetic mechanism.