Analysis of the chemical features of particles generated from ethylene and ethylene/2,5 dimethyl furan flames

Carbon particulate matter formed in fuel-rich atmospheric pressure premixed flames of ethylene and ethylene doped with 2,5 dimethyl furan (DMF) (20%) was analyzed in order to investigate the effect of fuel-borne oxygen on soot nanostructure and chemical functionalities. Particles were thermophoretically sampled on quartz plates and analyzed by techniques sensitive to the particle internal structure, namely FTIR, Raman and UV-vis spectroscopy. In nearly identical temperature, equivalence ratio and residence time conditions, the concentration of particulate generated in the biofuel-doped flame was found to be far less of the concentration of ethylene flame particulate. The similarity of UV-vis and Raman spectra showed that DMF addition to ethylene did not significantly change the aromatization process of carbon particulate in the flame. Complementary information on the functional groups located at the edge of the polyaromatic system was probed by FTIR analysis. FTIR spectra showed to be very similar regarding the carbon network in particles produced in both flames. However, the infrared spectrum of the particles produced in the ethylene/DMF flame presented less intense peaks of aromatic hydrogen (900-700 cm−1) and a higher absorption in the 1300-1100 cm−1 wavenumber range. These changes in the infrared spectra were attributed to a higher amount of oxygen atoms that substitute hydrogen atoms at the edges of aromatic clusters of the ethylene/DMF soot particles. Oxygen content was estimated to be larger by few percentages in particles from ethylene/DMF with respect to particles from pure ethylene. This could be the cause for the enhanced reactivity of soot particles generally found for biofuel-derived soot.