Influence of substituted furans on the formation of Polycyclic Aromatic Hydrocarbons in flames

Abstract

The structure of low-pressure (40kPa) rich laminar premixed flames of two potential new biofuels, 2,5-dimethylfuran (DMF) and 2-methylfuran (MF), has been investigated using gas chromatography after sampling by a sonic probe. This work follows a study of the same flames made using electron-ionization molecular-beam mass spectrometry (EI-MBMS). Temperature profiles have been measured using a thermocouple with and without the probe and compared with those obtained during EI-MBMS experiments, showing the important influence of the probe geometry. The mole fraction profiles above the burner of numerous products and intermediates (31 for MF, 40 for DMF) have been quantified, including all the isomers which were globalized during EI-MBMS experiments, as well as some heavier aromatic products such as ethylbenzene and styrene. The profiles of these aromatics confirmed their significantly enhanced formation in the case of DMF compared to MF, which was already shown in the previous study. The model of the oxidation of these two substituted furans have been up-dated to include new reactions for the formation of C8 aromatics, as well as reactions proposed in literature for large Polycyclic Aromatic Hydrocarbons (PAH) formation. Simulations show a significant enhancement effect on the formation of PAH, such as pyrene or phenanthrene: their maximum mole fractions are increased by a factor of more than 400 in the DMF flame compared to that of MF, while it is only a factor 3 in the case of benzene. Simulations show that PAH mole fractions are also slightly larger in the DMF flame than in a flame of a gasoline surrogate containing toluene as an octane improver under the same conditions. However the PAH mole fractions in the DMF flame are significantly lower than in a flame of pure toluene, showing that this biofuel could be an interesting octane improver in replacement of aromatics.