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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.

Ignition delay times of 1-pentene-oxygen-argon mixtures have been measured behind shock wave, the onset of ignition being detected by OH radical emission. Mixtures contained 1 or 2% of hydrocarbon for equivalence ratios ranging from 0.5 to 2. Reflected shock waves allowed temperatures from 1130 to 1620 K and pressures from 7.3 to 9.5 atm to be obtained. A detailed mechanism of combustion of 1-pentene has been automatically generated using EXGAS software. This mechanism has been validated by comparing the results of the simulations to the experimental ignition delay times. The main reaction pathways have been derived from flow rate and sensitivity analyses at different temperatures. Comparisons with 1-butene and 1-hexene in the same conditions show that 1-pentene has a higher reactivity which seems to be due to its decomposition to give ethyl radicals, which rapidly yields very reactive hydrogen atoms, while the decomposition of 1-butene and 1-hexene leads to less reactive methyl radicals.

Simulations have been performed with spatial uniformity assumed, in order to assess the effect of tentative wall reactions on autoignition delay times and on a pressure -ambient temperature diagram of oxidation phenomena in the case of n-butane. Reactions which depend on the type of reactor wall coating have been considered for HO and RO radicals with estimated rate constants. The inhibiting effect of these walls has been simulated for closed vessel autoignition delay times as well as for ignition boundaries at pressures below 1 atm. The minimum temperature at which reaction occurs in jet-stirred reactor simulations is similarly affected 2 2.

This paper describes how automatically generated detailed kinetic mechanisms are obtained for the oxidation of alkanes and how these models could lead to a better understanding of autoignition and cool flame risks at elevated conditions. Examples of prediction of the occurrence of different autoignition phenomena, such as cool flames or two-stage ignitions are presented depending on the condition of pressure, temperature and mixture composition. Three compounds are treated, a light alkane, propane, and two heavier ones, n-heptane and n-decane.