No abstract

Total word count (Method 1) : 5571• Text : 3183• References : (33+2)x2.3x7.6 = 612• Table 1 : (5+2)x7.6x2 + 40 = 146 • Equations : (2+4)x7.6 = 46Ignition delay times of cyclohexane-oxygen-argon and cyclopentane-oxygen-argon mixtures have been measured in a shock tube, the onset of ignition being detected by OH radical emission.Mixtures contained 0.5 or 1 % of hydrocarbon for equivalence ratios ranging from 0.5 to 2.Reflected shock waves allowed temperatures from 1230 to 1800 K and pressures from 7.3 to 9.5 atm to be obtained. These measurements have shown that cyclopentane is much less reactive than cyclohexane, as for a given temperature the observed autoignition delay times were about ten times higher for the C 5 compound compared to the C 6 .Detailed mechanisms for the combustion of cyclohexane and cyclopentane have been proposed to reproduce these results. The elementary steps included in the kinetic models of the oxidation of cyclanes are close to those proposed to describe the oxidation of acyclic alkanes and alkenes.Consequently, it has been possible to obtain these models by using an improved version of software EXGAS, a computer package developed to perform the automatic generation of detailed kinetic models for the gas-phase oxidation and combustion of linear and branched alkanes and alkenes.Nevertheless, the modelling of the oxidation of cyclanes requires to consider new types of generic reactions, and especially to define new correlations for the estimation of the rate constants. Ab initio calculations have been used to better know some of the rate constants used in the case of cyclopentane. The main reaction pathways have been derived from flow rate and sensitivity analyses.

This paper presents a modelling study of the oxidation of cyclohexane from low to intermediate temperature (650-1050 K) including the negative temperature coefficient (NTC) zone. A detailed kinetic mechanism has been developed using computer-aided generation. This comprehensive low temperature mechanism involves 513 species and 2446 reactions and includes two additions of cyclohexyl radicals to oxygen, as well as, subsequent reactions. The rate constants of the reactions involving the formation of bicyclic species (isomerizations, formation of cyclic ethers) have been evaluated from data of the literature. This mechanism is able to reproduce satisfactorily experimental results obtained in a rapid compression machine, for temperatures ranging from 650 to 900K and in a jet stirred reactor from 750 to 1050 K. Flow rates analyses have been performed at low and intermediate temperatures.