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In this work, the ignition delay times of stoichiometric methane/dimethyl ether (DME) were measured behind the reflected shock waves over a wide range of conditions: temperatures between 1134 and 2105 K, pressures of 1, 5, and 10 bar, a DME blending ratio from 0 to 100% (M100 to M0), and an argon concentration of 95%. The present shock tube facility was validated by comparing the measured ignition delay times of DME with literature values and was used for measurement of the subsequent methane/DME ignition delay times. The ignition delay times of all mixtures exhibit a negative pressure dependence. For a given temperature, the ignition delay time of methane/DME decreases remarkably with the presence of only 1% DME. As the DME blending ratio increases, the ignition delay times are correspondingly decreased; however, the ignition promotion effect of DME is decreased. The calculated ignition delay times of methane/DME mixtures using two recently developed kinetic mechanisms are compared with those of measurements. The NUI C4 mechanism yields good prediction for the ignition delay time of methane. With an increase of the DME blending ratio, the performance of this model becomes moderated. Zhao’s DME model yields good prediction for all of the mixtures studied in this work; thus, it was selected for analyzing the ignition kinetics of methane/DME fuel blends, through which the nonlinear effect of DME addition in promoting ignition is interpreted.

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Ignition delay times for 1% cyclopentane/O 2 and 0.833% methylcyclopentane/O 2 mixtures diluted by argon were measured behind reflected shock waves at pressures of 1.1 and 10 atm, with equivalence ratios of 0.577, 1.0, and 2.0, and in the temperature range from 1150 to 1850 K. Submechanisms for cyclopentane and methylcyclopentane were developed and added to the JetSurF2.0 mechanism for the kinetic interpretation of cyclopentane and methylcyclopentane oxidation chemistry at the high temperature region. Simulations with the model exhibit fairly good agreements with the measured ignition delay times of both cyclopentane and methylcyclopentane under all tested conditions. Cyclopentane shows longer ignition delay time than methylcyclopentane, especially for the fuel-lean mixture. Reaction pathways and sensitivity analyses were conducted to get insights into the oxidation process of cyclopentane and methylcyclopentane. Then, three factors are given for the effect of a cyclic ring and substitution of a methyl group. Substitution of a methyl group weakens the C−C bond to motivate fuel unimolecular decomposition. The shape of the cyclic ring determines the chain alkyl radicals, affecting regeneration and accumulation of H radical. The presence of a methyl group also leads to different alkyl radicals.

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