Primary combustion intermediates in low-pressure premixed laminar 2,5-dimethylfuran/oxygen/argon flames

Primary combustion intermediates in low-pressure premixed laminar 2,5-dimethylfuran (DMF)/oxygen (O₂)/argon (Ar) flames with equivalence ratios of 0.8 and 1.5 were investigated by using tunable synchrotron vacuum ultraviolet photoionization and molecular-beam mass spectrometry. DMF is a promising biofuel, with properties similar to those of gasoline. However, the combustion chemistry of DMF is not well-studied. Possible reaction pathways of DMF and its primary combustion derivatives were proposed based on the combustion intermediates identified in this work. Photoionization efficiency curves (PIEs) of the combustion intermediates in the DMF/O₂/Ar flames were recorded. Ionization energies (IEs) were measured from the PIEs. The combustion intermediates were identified by the agreement of the measured IEs with those reported in the literatures or calculated at G3B3 level. H abstraction and the consecutive reaction products were identified, including 5-methylfurfural, (Z)-1-oxo-1,3,4-pentatriene, and 2-ethyl-5-methylfuran, etc. Furan was not observed in the low-pressure DMF flames. H and OH addition products were also identified, including 2-methylfuran, (2Z,3E)-1-oxo-1,3-pentadiene, and 2-oxo-2,3-dihydro-5-methylfuran. The extra methyl side chain may explain the lower laminar burning velocity of DMF relative to that of 2-methylfuran.