Exploring the low-temperature oxidation chemistry of cyclohexane in a jet-stirred reactor: An experimental and kinetic modeling study

We report the investigation on the low-temperature oxidation of cyclohexane in a jet-stirred reactor over 500-742K. Synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) was used for identifying and quantifying the oxidation species. Major products, cyclic olefins, and oxygenated products including reactive hydroperoxides and high oxygen compounds were detected. Compared with n-alkanes, a narrow low-temperature window (∼80K) was observed in the low-temperature oxidation of cyclohexane. Besides, a kinetic model for cyclohexane oxidation was developed based on the CNRS model [Combust. Flame 160, 2319 (2013)], which can better capture the experimental results than previous models. Based on the modeling analysis, the 1,5-H shift dominates the crucial isomerization steps of the first and second O₂ addition products in the low-temperature chain branching process of cyclohexane. The negative temperature coefficient behavior of cyclohexane oxidation results from the reduced chain branching due to the competition from chain inhibition and propagation reactions, i.e. the reaction between cyclohexyl radical and O₂ and the decomposition of cyclohexylperoxy radical, both producing cyclohexene and HO₂ radical, as well as the decomposition of cyclohexylhydroperoxy radical producing hex-5-en-1-al and OH radical.