On the two-stage auto-ignition of butyl nitrite isomers

In response to the interest in nitrogen-containing compounds as energetic materials, an experimental and kinetic study on the low-temperature oxidation of three butyl nitrites isomers, namely n‑butyl (NBN), isobutyl (IBN), and tert‑butyl (TBN) was performed. By measuring their ignition delays in a rapid compression machine (RCM) under 5–15 bar at temperatures from 550 to 630 K, a two-stage ignition behavior was observed for all the three nitrites, with the first-stage delays of TBN being shorter than those of NBN and IBN. A detailed kinetic mechanism was constructed and validated against the experimental data, and the production rate was analyzed to explain the first-stage ignition behavior. Specifically, the N−O bond dissociation reaction initiated the consumption of butyl nitrites isomers in all cases studied, which produced NO and different butoxy radicals (C₄H₉O). In the case of TBN, the decomposition of TC₄H₉O produces CH₃ in the first-stage ignition. The abundant CH₃ radical reacts with NO₂ to produce CH₃O, which further yields HO₂ and CH₂O through the reaction with O₂. The inert HO₂ radical is converted to OH through the reaction HO₂ + NO = OH + NO₂, resulting in the first-stage ignition. Meanwhile, the decomposition of PC₄H₉O and IC₄H₉O produces n-propyl and i-propyl radicals, respectively, in the cases of NBN and IBN. The reaction sequences of n-propyl and i-propyl radicals produce less HO₂ radicals compared with that in TBN, leading to longer first-stage ignition time.