Kinetic Modeling of Cyclohexane and n-Propylcyclohexane Oxidation with the PAH Precursor Formation

Abstract

A reaction mechanism of cyclohexane (cyC6H12) and n-propylcyclohexane (cyC9H18) is developed to study its oxidation at both low and high temperatures, including PAH precursors routes. The cyclohexane oxidation kinetic mechanism is a significant update of the model developed earlier in DLR. The new cyC6H12 model is based on the most recent studied C0-C3 chemistry and includes the PAH sub-model up to 5-ringed molecules. Improvements have been done through the rivaling the main reaction classes, uncertainty boundaries of the rate coefficients and an inclusion of two additive low-temperature reaction pathways: cyclohexenyl peroxy formation, and isomerization of hydroperoxy peroxy radical. The cyC6H12 mechanism, successfully validated on the ignition delay data from rapid compression machines (RCM) and shock tube experiments, as well as laminar flame speed data and concentration profiles, model was then further extended to the n-propylcyclohexane oxidation model. For our knowledge, the low-temperature cyC9H18 oxidation scheme was earlier not presented in the literature. It is shown, that unlike cyC6H12 the low-temperature ignition of n-propylcyclohexane demonstrates negative temperature coefficient (NTC) behavior. The pathways towards production of benzene as the first aromatics was investigated under the different temperature regimes.