Shock Tube Measurements and Kinetic Investigation on the Ignition Delay Times of Methane/Dimethyl Ether Mixtures

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

Shock Tube Measurements and Kinetic Study on Ignition Delay Times of Lean DME/<i>n</i>‑Butane Blends at Elevated Pressures

In this study, the ignition delay times of lean DME/<i>n</i>-C₄H₁₀ fuel blends diluted with argon were measured behind reflect shock waves over a wide range of conditions: pressures from 0.2 to 2.0 MPa, temperatures from 1100 to 1600 K, and DME blending ratios from 0 to 100%. The results show that for all of the mixtures, an increase in pressure significantly promotes the ignition of the fuel blends. An empirical Arrhenius correlation with high fidelity was proposed and was used to calculate the ignition delay times of DME/<i>n</i>-C₄H₁₀. Under fuel-lean conditions, both neat DME and neat <i>n</i>-C₄H₁₀ present almost uniform global activation energies. For a given temperature and/or pressure, the ignition delay time is considerably insensitive to changes in the DME blending ratio. Comparisons of the predictions by five available kinetic mechanisms with the measured ignition delay times were made, and NUIG Aramco Mech 1.3 was found to give excellent predictions for all of the tested mixtures. Hence, NUIG Aramco Mech 1.3 was used to make the kinetic analysis, including fuel flux analysis, sensitivity analysis, and mole fraction analysis of key radicals, and to interpret the effect of DME addition on the ignition chemistry of <i>n</i>-C₄H₁₀

Experimental and Modeling Study of <i>n</i>-Butanol Oxidation at High Temperature

Ignition delay times of <i>n</i>-butanol/oxygen diluted with argon were measured behind reflected shock waves. Experiments were carried out in the temperature range 1200–1650 K, at 2 and 10 atm, and at equivalence ratios of 0.5, 1.0, and 2.0. Correlations of ignition delay times were constructed on the basis of measured data through multiple linear regression. A modified kinetic model for the oxidation of <i>n</i>-butanol at high temperature was developed, based on previous models by adding and modifying some key reactions. The modified model shows good prediction of the measured data under all measured conditions. This model was also validated against jet-stirred reactor (JSR) data obtained from the literature, and fairly good agreement was observed. A fair improvement on the simulation of aldehydes (acetaldehyde and butyraldehyde) was found compared to the original model. Finally, reaction pathway and sensitivity analysis indicate that the H-abstraction reactions play a dominant role in the consumption of <i>n</i>-butanol, while unimolecular decomposition reactions become more important with increasing temperature. High-level accurate investigation of the rate constants of H-abstraction reactions and unimolecular decomposition reactions is required to further improve <i>n</i>-butanol oxidation kinetics