Comparative Study on Cyclohexane and Decalin Oxidation

Fuel surrogates are mixtures of a few single aliphatic and aromatic compounds representative of the main classes of hydrocarbons present in the corresponding fuels. Among these hydrocarbon classes, the cycloalkanes constitute one of the key components in several surrogate formulations. In the present investigation, the oxidation of cyclohexane and decalin has been studied based on new experimental results. The experiments were obtained using two different techniques. A heated shock tube was used to conduct ignition delay time measurements at different stoichiometric conditions, nominal pressure of around 10 bar, and temperatures between 1090 and 1860 K. Ignition delay times in the range between 10 and 1300 μs were measured from both the OH* and the CH* emission signals behind reflected shock waves for highly diluted mixtures (99% argon bath gas). Experiments were also conducted varying the dilution from 99.5% to 92.7% for specific stoichiometric conditions. In addition to the ignition studies, flame speed measurements were performed using a spherical bomb heated to 403 K. Experiments were conducted varying the equivalence ratio between 0.6 and 1.5 at an initial pressure of 1 bar. Similar experimental profiles were obtained for the two species with maximum flame speeds equal to 62.1 cm/s at Φ ≈ 1.05 for cyclohexane and 56.5 cm/s at Φ ≈ 1.07 for decalin. Both the ignition delay time and flame speed experimental results were accurately simulated using chemical kinetic models available in the literature. Subsequent modeling analyses were carried out in order to clarify the role of the single- and double-ring structures on the experimental combustion properties of the two representative compounds studied herein.