Experimental Study of Tetrahydrofuran Oxidation and Ignition in Low-Temperature Conditions

The chemistry associated with low-temperature oxidation and ignition of tetrahydrofuran (THF) has been probed through experimental work in two distinct devices: a rapid compression machine (RCM) and a jet-stirred reactor (JSR). Ignition delays of stoichiometric THF/O-2/inert mixtures have been measured for pressures ranging from 0.5 to 1.0 MPa and core gas temperatures from 640 to 900 K. Two-stage ignition is visible up to 810 K, and the evolution of the ignition delay with the temperature shows a clear deviation from Arrhenius behavior between 680 and 750 K. Sampling of the reactive mixture during the ignition delay provided evidence of the formation of C-1-C-4 aldehydes and alkenes, a variety of oxygenated heterocycles, including oxirane, methyloxirane, oxetane, furan, both isomers of dihydrofuran, and 1,4-dioxene, as well as cyclopropanecarboxaldehyde and formic acid-2-propenyl ester. JSR experiments have been performed under pressure close to 1 atm, at temperatures from 500 to 1000 K, and at equivalence ratios from 0.5 to 2, with detailed analysis of the low-temperature intermediate products. Major products include carbon monoxide, carbon dioxide, C-1-C-2 hydrocarbons, and aldehydes, 1-butene, ethylene oxide, methylvinylether, acrolein, propanal, both isomers of dihydrofuran, furan, 2-butenal, cyclopropanecarboxaldehyde, 1,4-dioxene, and unsaturated dihydrofuranols. The obtained mole fraction profiles indicate a significant low-temperature reactivity of THF beginning at temperatures around 550 K, with a marked negative temperature coefficient zone. The results from both experimental devices are put in perspective and allow for the identification of the major formation pathways of the observed species.