Formation and nanoscale-characteristics of soot from pyrolysis of ethylene blended with ethanol/dimethyl ether

Ethanol and dimethyl ether (DME) have been considered to be two of the most potential additives for conventional hydrocarbon fuels. This paper focused on the nanoscale characteristics of soot from ethylene pyrolysis with ethanol and DME additions. The pyrolysis experiments were conducted in a alpha-alumina tube flow reactor at 1273 K, 1373 K and 1473 K, with the replacement of 0%, 50% and 100% (mole fraction) ethylene by the two oxygenated fuels. The gas-phase kinetic modeling was also performed to explore and understand the soot formation process. The main pathways and some key soot precursors in the pyrolysis have been obtained. Soot samples were characterized by high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) to acquire their internal structure and oxidation reactivity. Results showed that the mass of collected soot diminished with the increase of the replacement of ethylene by ethanol/DME. The effects of DME to inhibit the formation of soot were more obvious. The least amount of soot was collected in the pyrolysis of pure DME. Peak mole fraction of C2H2, C4H2, C4H4 and C5H5 also decreased with the increase of replacement of ethylene by ethanol/DME, displaying the same tendency with the variation trend of soot mass in the different pyrolysis conditions. According to TEM and HRTEM results, the additions of ethanol and DME could decrease the growth rate of soot contrasted with the pyrolysis of pure ethylene. Soot collected from the pyrolysis of pure DME at 1273 K and 1373 K showed a typical amorphous structure with short, highly-curved and turbulent fringe. With the reduction of the replacement of ethylene by DME, mature soot with longer and more ordered fringe formed at 1373 K and 1473 K. The sequence of the mean fringe tortuosity of soot samples was 100% ethylene<50% DME<100% ethanol<50% ethanol< 100% DME. The order was the same as the sequence of oxidation reactivity. Furthermore, with the increase of temperature, the mass of soot increased. More mature soot with higher degree of graphization, longer fringe length, smaller fringe tortuosity and lower oxidation reactivity was obtained. High correlation between soot nanostructure and soot oxidation reactivity was found. (C) 2020 Energy Institute. Published by Elsevier Ltd. All rights reserved.