High-temperature pyrolysis and oxidation of nitromethane: laser diagnostics and model development for C–N–O combustion chemistry

A detailed experimental and modeling study was conducted to investigate the high-temperature decomposition and ignition behavior of nitromethane (CH 3 NO 2 ) and its relevance to the development of a comprehensive C–N–O kinetic model. Shock tube experiments coupled with high temporal resolution and low detection limit laser absorption diagnostics were employed to measure time-resolved species profiles of NO, CO, and CH 4 during CH 3 NO 2 pyrolysis under argon-diluted conditions (1.0 % and 1.3 % CH 3 NO 2 in Ar). In addition, ignition delay times (IDTs) of CH 3 NO 2 /O 2 /Ar mixtures were measured over a wide range of equivalence ratios ( φ = 0.5, 1.0, and 2.0) at near-atmospheric pressure. To further constrain the kinetics, the rate constant for the unimolecular decomposition reaction R1 (CH 3 NO 2 (+M)=> CH 3 + NO 2 (+M)) was experimentally determined at high temperatures, the resulting rate constant data can be represented by the Arrhenius equation k R1 (1043–1350 K, 1.5 atm) = 4.98 × 10 12 exp(-44,990 cal/mol/ RT ) s -1 . A refined kinetic model for CH 3 NO 2 combustion was developed by integrating the newly obtained rate constant data of R1 and updating the CH 3 NO 2 sub-mechanism within a previously established NH 3 –syngas model. Rate of production and sensitivity analyses were performed to identify the dominant reaction pathways governing species formation, with particular emphasis on the role of R1 and its competition with secondary reactions. This work advances the understanding of nitroalkane combustion, offering a robust and transferable kinetic framework for future simulations of energetic materials in propulsion and energy systems.