A systematic study of the ignition behavior of furan and the substituted furans 2-methyl furan (2-MF) and 2,5dimethyl 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 ϕ, 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 ϕ, 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.

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Abstract:There is growing interest in the use of furans, a class of alternative fuels derived from biomass, as transportation fuels. This paper reviews recent progress in the characterization of its combustion properties. It reviews their production processes, theoretical kinetic explorations and fundamental combustion properties. The theoretical efforts are focused on the mechanistic pathways for furan decomposition and oxidation, as well as the development of detailed chemical kinetic models. The experiments reviewed are mostly concerned with the temporal evolutions of homogeneous reactors and the propagation of laminar flames. The main thrust in homogeneous reactors is to determine global chemical time scales such as ignition delay times. Some studies have adopted a comparative approach to bring out reactivity differences. Chemical kinetic models with varying degrees of predictive success have been established. Experiments have revealed the relative behavior of their combustion. The growing body of literature in this area of combustion chemistry of alternative fuels shows a great potential for these fuels in terms of sustainable production and engine performance. However, these studies raise further questions regarding the chemical interactions of furans with other hydrocarbons. There are also open questions about the toxicity of the byproducts of combustion.

A combined experimental and chemical kinetic modeling study of the high-temperature ignition and pyrolysis of 1,3-dimethylcyclohexane (13DMCH) is presented. Ignition delay times are measured behind reflected shock waves over a temperature range of 1049–1544 K and pressures of 3.0–12 atm. Pyrolysis is investigated at average pressures of 4.0 atm at temperatures of 1238, 1302, and 1406 K. By means of mid-infrared direct laser absorption at 3.39 μm, fuel concentration time histories are measured under ignition and pyrolytic conditions. A detailed chemical kinetic model for 13DMCH combustion is developed. Ignition measurements show that the ignition delay times of 13DMCH are longer than those of its isomer, ethylcyclohexane. The proposed chemical kinetic model predicts reasonably well the effects of equivalence ratio and pressure, with overall good agreement between predicted and measured ignition delay times, except at low dilution levels and high pressures. Simulated fuel concentration profiles agree reasonably well with the measured profiles, and both highlight the influence of pyrolysis on the overall ignition kinetics at high temperatures. Sensitivity and reaction pathway analyses provide further insight into the kinetic processes controlling ignition and pyrolysis. The work contributes toward improved understanding and modeling of the oxidation and pyrolysis kinetics of cycloalkanes.