Kinetic Modeling of Cyclohexane Oxidation Including PAH Formation

Abstract

A reaction mechanism for cyclohexane (cyC 6 H 12) is developed to study its oxidation at both low and high temperatures, including PAH formation. Based on values of rate coefficients available in literature, uncertainty analyses has been performed for each reaction class included in the mechanism, and the optimum values are implemented in the cyC 6 H 12 sub-mechanism. Furthermore, reactions of bi-cyclic ethers and cylohexanone decompositions via further dehydrogenation steps and ring-opening leading to smaller olefins and ketone radicals were implemented. Thermochemical properties of the main species of the low-temperature sub-mechanism are determined by applying the group additivity method of Benson. The properties of some new Benson's groups, including ring corrections for cycling species were estimated. The ignition delay data from rapid compression machines (RCM) and shock tube experiments and also laminar flame speed data have been used for the model validation. The concentration profiles of the soot precursor species from burner-stabilized premixed flames experiments at different pressures and temperatures are well predicted by the current model.

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

“…This path is competitive with the lowtemperature hexyl oxidation. The developed cyC6H12 model [26] satisfactorily reproduces the experimental data for ignition delay times, laminar flame speeds and concentration profiles measured in laminar flames. That makes it valuable for the application as a basic model in development of the kinetics schemes for larger and substituted naphthenes.…”

“…The current kinetic mechanism implies C0-C2 chemistry from the recent researches of Slavinskaya et al, [28,29] the further improvements of the cyclohexane oxidation model developed by Abbasi et al [26] and the n-propylcyclohexane reactions scheme established in Slavinskaya et al [25].…”

“…The cyclohexane oxidation model of Abbasi et al [26] were extended with two additive pathways: isomerization of cyOOC6H10OOH through the internal hydrogen transfer yielding more stable cyC6H9(OOH)2 and the secondary low-temperature cyclohexene, cyC6H10, oxidation. The possible isomers of cyC6H9(OOH)2 were grouped in a single lumped component, which dissociates into cyclic ketohydroperoxide and OH.…”

“…Only few studies were published [3,23,24] concerning mostly high-temperature oxidation of the cyC9H18. In the present paper, the earlier developed [25] cyC9H18 oxidation model was analyzed and is modified and further developed on the basis of the recently updated and extended cyC6H12 model [26]. The uncertainty of the key reaction types for both high-and low-temperature scheme have been evaluated.…”

Low Temperature Oxidation of Cyclohexane: Uncertainty of Important Thermo-Chemical Properties

“…The chemistry of cyC 6 H 12 oxidation is the basis for the reaction mechanisms of combustion of different naphthenes, including substituted cyclo-molecules. The present study revises the thermodynamic data for the molecules and radicals involved in the low-temperature chemical kinetics of cyC 6 H 12 [1] and estimates thermodynamic properties for molecules adopted in the model during modifications and extensions. Figure 1 depicts the main reaction paths and species of the low-temperature sub-mechanism of the DLR cyclohexane combustion model [ The current reaction mechanism [1] has been extended for the cyclohexene low-temperature schemes (step 13), for cyclohexenyl peroxy formation and isomerization of hydroperoxy peroxy radical, through the internal hydrogen transfer yielding more stable cyC 6 H 9 (OOH) 2 (step 7).…”