A comprehensive experimental and detailed chemical kinetic modelling study of 2,5-dimethylfuran pyrolysis and oxidation

摘要

The pyrolytic and oxidative behaviour of the biofuel 2,5-dimethylfuran (25DMF) has been studied in a range of experimental facilities in order to investigate the relatively unexplored combustion chemistry of the title species and to provide combustor relevant experimental data. The pyrolysis of 25DMF has been re-investigated in a shock tube using the single-pulse method for mixtures of 3% 25DMF in argon, at temperatures from 1200 to 1350 K, pressures from 2 to 2.5 atm and residence times of approximately 2 ms. Ignition delay times for mixtures of 0.75% 25DMF in argon have been measured at atmospheric pressure, temperatures of 1350-1800 K at equivalence ratios (φ) of 0.5,1.0 and 2.0 along with auto-ignition measurements for stoichiometric fuel in air mixtures of 25DMF at 20 and 80 bar, from 820 to 1210 K. This is supplemented with an oxidative speciation study of 25DMF in a jet-stirred reactor (JSR) from 770 to 1220 K, at 10.0 atm, residence times of 0.7 s and at φ = 0.5, 1.0 and 2.0. Laminar burning velocities for 25DMF-air mixtures have been measured using the heat-flux method at unburnt gas temperatures of 298 and 358 K, at atmospheric pressure from φ = 0.6-1.6. These laminar burning velocity measurements highlight inconsistencies in the current literature data and provide a validation target for kinetic mechanisms. A detailed chemical kinetic mechanism containing 2768 reactions and 545 species has been simultaneously developed to describe the combustion of 25DMF under the experimental conditions described above. Numerical modelling results based on the mechanism can accurately reproduce the majority of the experimental data. At high temperatures, a hydrogen atom transfer reaction is found to be the dominant unimolecular decomposition pathway of 25DMF. The reactions of hydrogen atom with the fuel are also found to be important in predicting pyrolysis and ignition delay time experiments. Numerous proposals are made on the mechanism and kinetics of the previously unexplored intermediate temperature combustion pathways of 25DMF. Hydroxyl radical addition to the furan ring is highlighted as an important fuel consuming reaction, leading to the formation of methyl vinyl ketone and acetyl radical. The chemically activated recombination of HO_2 or CH_3O_2 with the 5-methyl-2-furanylm-ethyl radical, forming a 5-methyl-2-furylmethanoxy radical and OH or CH_3O radical is also found to exhibit significant control over ignition delay times, as well as being important reactions in the prediction of species profiles in a JSR. Kinetics for the abstraction of a hydrogen atom from the alkyl side-chain of the fuel by molecular oxygen and HO_2 radical are found to be sensitive in the estimation of ignition delay times for fuel-air mixtures from temperatures of 820 to 1200 K. At intermediate temperatures, the resonantly stabilised 5-methyl-2-furanylmethyl radical is found to predominantly undergo bimolecular reactions, and as a result sub-mechanisms for 5-methyl-2-formylfu-ran and 5-methyl-2-ethylfuran, and their derivatives, have also been developed with consumption path- ways proposed. This study is the first to attempt to simulate the combustion of these species in any detail, although future refinements are likely necessary. The current study illustrates both quantitatively and qualitatively the complex chemical behaviour of what is a high potential biofuel. Whilst the current work is the most comprehensive study on the oxidation of 25DMF in the literature to date, the mechanism cannot accurately reproduce laminar burning velocity measurements over a suitable range of unburnt gas temperatures, pressures and equivalence ratios, although discrepancies in the experimental literature data are highlighted. Resolving this issue should remain a focus of future work.