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 (CH₃NO₂) 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 CH₄ during CH₃NO₂ pyrolysis under argon-diluted conditions (1.0 % and 1.3 % CH₃NO₂ in Ar). In addition, ignition delay times (IDTs) of CH₃NO₂/O₂/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 (CH₃NO₂ (+M)=> CH₃ + NO₂ (+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 × 10¹² exp(-44,990 cal/mol/RT)s^-1. A refined kinetic model for CH₃NO₂ combustion was developed by integrating the newly obtained rate constant data of R1 and updating the CH₃NO₂ sub-mechanism within a previously established NH₃–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.