Experimental and kinetic modeling of the ignition delays of cyclohexane, cyclohexene, and cyclohexadienes: Effect of unsaturation

Cyclic and aromatic hydrocarbons are important components of usual commercial fuels, with C 6-rings being among the most abundant cyclic structures. The combustion chemistry of C-6-rings involves different levels of unsaturation, either as initial fuels (aromatics, naphtenes,.) or as intermediates formed during their combustion. In this work the ignition delays of cyclohexane, cyclohexene, 1,3-cyclohexadiene and 1,4cyclohexadiene are systematically studied using experiments and kinetic modeling. Shock tube experiments were performed at high-temperature (above 1200 K) and for mean pressures of 6 atm. A detailed chemical kinetic model was developed that includes the combustion chemistry of the four cyclo-C 6 fuels. Electronic structure calculations were performed at the CCSD(T)/CBS//B2PLYP-D3 level of theory on the pericyclic reactions of the unsaturated fuels. Pressure-dependent rate coefficients were computed by solving the master equation, and included in the mechanism. The model was validated against the new ignition data and against data of the literature. It was able to reproduce the experimental ranking of reactivity: cyclohexene > 14-CHD > cyclohexane > benzene similar to 13-CHD. Kinetic analyses were performed to explain this difference of reactivity. It is shown that pericyclic reactions play a major role in the initial decomposition of the unsaturated fuels. (c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

This study systematically investigated the ignition delays of cyclohexane, cyclohexene, 1,3-cyclohexadiene, and 1,4cyclohexadiene using experiments and kinetic modeling. The results showed that cyclohexene had the highest reactivity, followed by 14-CHD, cyclohexane, and benzene similar to 13-CHD. Pericyclic reactions were found to play a major role in the initial decomposition of the unsaturated fuels.