Effects of ethanol and 2, 5-dimethylfuran addition on the morphology and nanostructure evolution of soot in gasoline primary reference fuel-air coflow diffusion flames

The sediment morphology and oxidation activity of soot at different heights above the burner are studied for three fuels. The three fuels are n-heptane/iso-octane mixtures (0% 2, 5-dimethylfuran and 0% ethanol, DE0), n-heptane/isooctane mixture with 15% ethanol (E15) and n-heptane/iso-octane mixture with 15% 2, 5-dimethylfuran (DMF15). Oxygenated fuel increases flame height and decreases flame brightness. DMF15 has the highest flame and has a brighter waist edge. From the field emission scanning electron microscopy (FESEM) images, ethanol and 2-5, dimethylfuran (DMF) make the deposits particle size of soot smaller and uniform. The soot deposits at the height of the flame became more orderly, E15 soot with the smallest fibrous deposits and pore structure. Donut and Steamed bun structures are found in soot sediments of DE0 and DMF15, which had not been previously reported. The results of thermogravimetric analysis (TGA) show that the oxidation activity of soot in different flame positions is very different. Generally, the activation energy of soot increases with the increase of sampling position, but the activation energy of DMF15 soot decreases first and then increases. Finally, the soot activation energy of E15 and DMF15 is much less than that of DE0, and E15 has the highest oxidation activity. It is inferred that the structure of the special soot deposits is caused by the inhomogeneous oxidation activity on the surface of the deposits, therefore, a free radical erosion sediments model is proposed.