Experimental and modeling study of cycloalkanes oxidation

摘要

Fuel surrogates are mixtures of 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 such cases, the chemistry of these compounds has a considerable impact on the accuracy of the surrogate approach in terms of prediction capability for real-engine applications. 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 (equivalence ratio between 1.5 and 0.2), 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). Additional experiments were conducted varying the dilution from 99.5% to 92.7% for specific stoichiometric conditions. Experimental correlations were derived and showed similar overall activation energies for the two compounds of interest (Ea = 40.4 and 44.6 kcal/mol for cyclohexane and decalin respectively). In addition to the ignition studies, flame speed measurements were performed using a spherical bomb heated to 403 K. The unstretched laminar flame speeds were derived using the asymptotic theory of flames and thermodynamic calculations. Experiments were conducted varying the equivalence ratio between 0.60 and 1.74 at an initial pressure of 1 bar. Once again, similar experimental profiles were obtained for the two species with maximum flame speeds equal to 62.3 cm/s at Φ ～ 1.08 for cyclohexane and 57.6 cm/s at Φ ～ 1.05 for decalin. The experimental results have been simulated using chemical kinetic models available in literature.