An experimental and kinetic modeling study of n-butylcyclohexane over low-to-high temperature ranges

Abstract

Cycloalkanes with long alkylic side chains are important chemical components in diesel and jet fuels. Although with the increasing interest in their combustion chemistry, related studies are very limited. In the present study, ignition delay times were measured for n-butylcyclohexane by combining a heated rapid compression machine and a heated shock tube. The data was obtained for equivalence ratios of 0.5, 1 and 1.5, at pressures of 10, 15 and 20 bar and over the temperature range of 612–1374 K. It was found that n-butylcyclohexane displayed marked low temperature reactivity with a typical negative temperature coefficient behavior. A correlation was developed to reproduce the measured ignition delay times over the entire temperature ranges. The results showed that it can well estimate the ignition delay times in the testing conditions. The effects of operating parameters on ignition delay times, including temperature, pressure, equivalence ratio, oxygen concentration and dilution ratio, were systematically presented and discussed. In the present work, a published mechanism was tuned with some modifications and was used to simulate the autoignition of n-butylcyclohexane. This model accurately captured the effect of the operating parameters over a wide range of conditions, and the simulations were in satisfactory agreement with the experimental results. For a better understanding of the chemistry involved during the autoignition events, kinetic analyses were performed using the tuned mechanism to provide insight to the experimental results. Comparisons were also carried out with the datasets for other cycloalkanes over the same conditions to reveal the effect of the side chain, and the trends, i.e., the longer side chain contributes to the stronger low temperature reactivity, were highlighted and discussed.