The kinetic model of ethylcyclohexane combustion over a wide temperature range and its comprehensive validation

Abstract

An experimental and modeling study is performed to develop a high accuracy combustion model of ethylcyclohexane (ECH) over a wide temperature range. The shock tube experiments are conducted to determine ignition delay times for ECH/air mixtures at 678–1287 K. Extensive quantum-chemical calculations concerning the low temperature kinetics of ECH including oxygen addition to hydroperoxyalkyl (·QOOH) and the following decomposition of hydroperoxyalkylperoxy radicals (·OOQOOH) have been investigated at the level of CBS-QB3//M06-2X/6-311++G(d,p). Due to the mutual influence of hydrogen bond and ring structure, the species configuration needs to be carefully determined in order to obtain thermodynamic data and then kinetic parameters. Different temperature- and pressure-dependent rate constants are computed for the side chain of ECH, the ring part, and the part where the ring and the side chain intersect. The rate constants of the hydrogen migration reaction are compared with the values estimated by analogizing with linear alkanes. Obvious deviations are observed especailly at low temperature. A detailed kinetic model is developed based on the existing low temperature model of ECH with the replacement of reaction calculated in present work and the core mechanism of AramcoMech 3.0. The model is validated comprehensively with experimental results of ignition delay time, laminar flame speed and species concentration profiles in jet-stirred reactor (JSR), which shows a good prediction over a wide temperature range. The results of sensitivity analyses show that the computed reactions of ·QOOH and ·OOQOOH have a great impact on the low temperature oxidation of ECH, which help to accurately reproduce the negative-temperature-coefficient behavior of ECH ignition. The kinetic parameters obtained in this work are conductive to improve the combustion models of substituted cycloalkanes with alkyl side chains, and the obtained kinetic model with high accuracy of ECH can be used as a basis to develop model of jet fuel.