A comprehensive study on low-temperature oxidation chemistry of cyclohexane. II. Experimental and kinetic modeling investigation

Abstract

Low-temperature oxidation of cyclohexane is investigated in two jet-stirred reactors (JSRs) at 1.04 bar and the equivalence ratio of 0.25. Reactive hydroperoxides and highly oxygenated molecules are detected using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). The isomers of C6H10O (5-hexenal, cyclic ethers and cyclohexanone) are separated using gas chromatography combined with mass spectrometry (GC–MS). Detection of characteristic hydroperoxides verifies that the conventional two-stage oxygen addition channels and recently reported third oxygen addition channels both contribute to the low-temperature oxidation of cyclohexane. Conformation-dependent channels theoretically investigated in Part I of this work are found correlated with the experimental observations of ketohydroperoxide (KHP) and alkenyl-hydroperoxide (AnHP) intermediates. A new detailed kinetic model of cyclohexane oxidation is constructed with consideration of the investigated conformation-dependent pathways in Part I and the experimental revisit of OH attack reactions over 889–1301 K and 1.22–1.84 bar. The model is validated against the newly measured oxidation data in this work and previous experimental data over a variety of pressure, temperature and equivalence ratio conditions. Modeling analysis reveals that the KHP channel and AnHP channel dominate the chain-branching process under the investigated conditions. The third oxygen addition channels and bimolecular reaction channels are found to play less important roles under the investigated conditions, while these reactions can provide more significant contributions to OH formation under high-pressure and lean conditions.