High-Temperature Study of 2-Methyl Furan and 2-Methyl Tetrahydrofuran Combustion

The ignition behavior of methyl furan (2-MF) and methyl tetrahydrofuran (2-MTHF) is investigated using the shock tube technique. Experiments are carried out using homogeneous gaseous mixtures of fuel, oxygen, and argon with equivalence ratios, ϕ, of 0.5, 1.0, and 2.0 at average pressures of 3 and 12 atm over a temperature range of 1060–1300 K. In addition to ignition delay time measurements, fuel concentration time histories during ignition and pyrolysis of 2-MTHF are obtained by means of laser absorption spectroscopy using a He–Ne laser at a fixed wavelength of 3.39 µm. With respect to ignition delay times, it is observed that under similar conditions of equivalence ratio and argon/oxygen ratio (D), 2-MTHF has longer ignition delay times than 2-MF at 3 atm. In addition, 2-MTHF has longer ignition delay times than 2-MF at higher temperatures for the case of 12 atm and under the same conditions of ϕ and D. The higher reactivity of 2-MF, as indicated by shorter ignition delay times, is attributed to differences in chemical structure, whereby weaker C–H bond sites are more readily susceptible to radical attack than in 2-MTHF. It is observed that ignition delay times of 2-MTHF decrease with increasing equivalence ratio at 12 atm for fixed argon/oxygen ratio. Ignition delay times are compared with model predictions using recent chemical kinetic models of both fuels, showing that both models generally predict shorter ignition delay times than measured. The relatively higher absorption cross section of 2-MTHF at 3.39 µm allows for its concentration time histories to be determined and compared to model predictions. In line with the observed discrepancy in ignition predictions, predicted 2-MTHF concentration profiles are such that the fuel is shown to be more rapidly consumed than observed in the experiments. The study advances understanding of the combustion chemistry of these cyclic ethers that are potential alternative fuels.