Reactivity Trends in Furan and Alkyl Furan Combustion

A systematic study of the ignition behavior of furan and the substituted furans 2-methyl furan (2-MF) and 2,5-dimethyl furan (DMF) is presented. Ignition delay times are measured over a temperature range from 977 to 1570 K and pressures up to 12 atm for lean, stoichiometric, and rich mixtures of fuel, oxygen, and argon. It is found that when the equivalence ratio phi, the argon-to-oxygen ratio D, and pressure p are kept constant over a range of temperatures T, DMF generally has the longest, while 2-MF has the shortest, ignition delay times, and furan shows intermediate reactivity. Ignition delay times decrease with increasing equivalence ratios, except for DMF, which does not show a conclusive trend over the temperature range investigated. The experimental data are also found to agree with published ignition data, showing differences in some cases partly related to disparities in endwall and sidewall ignition measurements. The ignition delay times of 2-MF and DMF are compared to predictions using furan chemical kinetic models by Sirjean et al.(1) and Somers et al.(2) The models show qualitatively that DMF has longer ignition delay times than 2-MF under similar conditions of phi, D, p, and T, as revealed by the experiments. Quantitatively, the model predictions agree with experimental data at conditions similar to those used in their development, and deviations from experiment at other conditions are mostly related to unmatched temperature sensitivities over a wider temperature range, revealed by varying pressure and reduced dilution. The reported experimental data set contributes toward further understanding and improved modeling of the combustion of furans, a promising class of alternative fuels.