Shock tube and laser absorption study of C–N–Cl interactions relevant to ammonium perchlorate combustion

Abstract

High-temperature gas-phase interactions between chlorine- and nitrogen-bearing species relevant to ammonium-perchlorate (AP) propellant combustion were elucidated by coupling shock-tube laser-absorption measurements with a detailed kinetic model. Time-resolved HCl concentration profiles were obtained for four argon-diluted surrogates—0.3 % NH₃/0.3 % CCl₄, 0.5 % NH₃/0.3 % CCl₄, 0.2 % NH₃/0.2 % CCl₄/0.2 % CH₄, and 0.2 % NH₃/0.2 % CCl₄/0.2 % H₂—over 1158–1506 K at near-atmospheric pressure. A kinetic model consisting of 164 species and 1358 reactions, assembled from state-of-the-art CCl₄, H–Cl–O, NH₃/C₀–C₂, and N–Cl sub-models, reproduced the new HCl data alongside literature ignition-delay and speciation measurements with excellent accuracy. Sensitivity and rate-of-production analyses reveal a temperature-robust control structure in which HCl forms almost entirely through Cl-atom abstraction from NH₃, with Cl supplied by rapid CCl₄ dissociation; the barrierless Cl + H<=>HCl path dominates in H₂-containing mixtures, whereas competition from Cl + CH₄<=>CH₃ + HCl moderates HCl growth and channels carbon–nitrogen flux toward toxic HCN when CH₄ is present. Elevated temperature chiefly amplifies Cl production and suppresses NH₂ recombination, accelerating overall reactivity without altering the dominant pathways. The resulting benchmark HCl time-histories and rigorously validated model advance fundamental understanding of chlorine–nitrogen combustion chemistry and provide quantitative guidance for formulating halogenated energetic materials that maximise performance while limiting hazardous by-product formation. Importantly, the mechanism developed here may serve as a transferable gas-phase sub-model for future integration into comprehensive AP combustion frameworks, enabling more predictive simulations of real propellant systems.