Polar Aromatic Compounds in Soot from Premixed Flames of Kerosene, Synthetic Paraffinic Kerosene, and Kerosene-Synthetic Biofuels

Polar aromatic compounds (PACs) adsorbed on soot produced in laboratory premixed flames of fossil kerosene (Jet A-1), synthetic paraffinic kerosene (SPK), and Jet A-1/synthetic biofuels (2,5-dimethylfuran, methyloctanoate, diethylcarbonate, and 1-butanol) were characterized for the first time with the aim of shedding light on the combustion mechanisms and evaluating the environmental impact of these synthetic biofuels. The following families of compounds were fractionated from the soot extracts, and furthermore, their relative abundances were estimated: (a) oxa-AHs (xanthenes, benzoxanthene, alcoxy-AHs, furan derivatives ...); (b) aldehydes-AHs, (c) ketones-AHs; (d) quinones-AHs; (e) aromatic monocarboxylic acids; (f) aromatic hydroxy acids; (g) aromatic dicarboxylic acids; (h) nitrated-AHs (including amines, acridines, cinnoline derivatives, carbazoles...); and (i) nitro-AHs. The results obtained point out that overall, soot from Jet A-1/biofuel premixed flames is richer in PACs than soot from pure Jet A-1 and SPK. Out of the fuels studied, Jet A-1/1-butanol produces the highest concentrations of nitro-AHs (namely, nitrobenzaldehydes), aldehydes-AHs, and hydroxy-AHs (including two isomers of hydroxy-benzaldehyde), whereas Jet A-1/diethylcarbonate produces the highest concentrations of quinones-AHs (especially phenanthrene quinones) and large concentrations of nitrated-AHs. On the other hand, soot from Jet A-1/methyloctanoate is the richest one in mono-aromatic and dicarboxylic acids, aromatic hydroxyacids, nitrated-AHs, and esters. Combustion of the Jet A-1/2,5-dimethylfuran mixture emits the highest concentrations of ketones-AHs and oxa-AHs (namely, furan derivatives). We should remark that although the soot samples were obtained from premixed flames, the lab conditions being far from the industrial conditions, particularly in terms of pressure; the chemistry going on should not be so different that our findings could not be extrapolated to industrial conditions.