An experimental and modeling study of the propagation of cyclohexane and mono-alkylated cyclohexane flames

Abstract

Laminar flame speeds of cyclohexane/air, methylcyclohexane/air, ethylcyclohexane/air, n-propylcyclohexane/air, and n-butylcyclohexane/air mixtures were determined in the counterflow configuration at atmospheric pressure, unburned mixture temperature of 353K, and for a wide range of equivalence ratios. The results indicate that cyclohexane/air flames propagate somewhat faster than mono-alkylated cyclohexane/air flames. Flames of mono-alkylated cyclohexane compounds were found to have similar laminar flame speeds, from methylcyclohexane to n-butylcyclohexane, suggesting that the different alkyl groups have a secondary effect on flame propagation. The experiments were modeled using JetSurF (version 1.1) – a detailed kinetic model for the combustion of cyclohexane and its derivatives. Both experiment and model show satisfactory agreement with each other. Based on the analysis of the model results, the somewhat lower rates of mono-alkylated cyclohexane flame propagation are attributed to the greater production of propene and allyl and the increased H-atom scavenging by these C3 intermediates. Though these fuel-specific reaction kinetic features do not limit the overall oxidation rates, the distribution of the cracked products do exert influences on flame propagation, leading to the subtle differences in the laminar flame speeds observed experimentally.