Shock tube measurements of ignition delay timesand OH time-histories in dimethyl ether oxidation

摘要

Ignition delay times and OH concentration time-histories were measured in DME/O2/Ar mixturesbehind reflected shock waves. Initial reflected shock conditions covered temperatures (T5) from 1175 to1900 K, pressures (P5) from 1.6 to 6.6 bar, and equivalence ratios (Φ) from 0.5 to 3.0. Ignition delay timeswere measured by collecting OH* emission near 307 nm, while OH time-histories were measured using laserabsorption of the R1(5) line of the A–X(0,0) transition at 306.7 nm. The ignition delay times extended theavailable experimental database of DME to a greater range of equivalence ratios and pressures. Measuredignition delay times were compared to simulations based on DME oxidation mechanisms by Fischer et al.[7] and Zhao et al. [9]. Both mechanisms predict the magnitude of ignition delay times well. OH time-historieswere also compared to simulations based on both mechanisms. Despite predicting ignition delaytimes well, neither mechanism agrees with the measured OH time-histories. OH Sensitivity analysis wasapplied and the reactions DME (→) CH3O+ CH3 and H + O2 (→) OH + O were found to be most important.Previous measurements of DME (→) CH3O+CH3 are not available above 1220 K, so the rate wasdirectly measured in this work using the OH diagnostic. The rate expression k[1/s] = 1.61×079 T-18.4exp(-58600/T), valid at pressures near 1.5 bar, was inferred based on previous pyrolysis measurementsand the current study. This rate accurately describes a broad range of experimental work at temperaturesfrom 680 to 1750 K, but is most accurate near the temperature range of the study, 1350–1750 K. When thisrate is used in both the Fischer et al. And Zhao et al. Mechanisms, agreement between measured OH andthe model predictions is significantly improved at all temperatures.