Effect of C9H12 alkylbenzenes on particle formation in diffusion flames: An experimental study

The sooting tendency of three C9H12 isomers, specifically n-propylbenzene, iso-propylbenzene and 1,3,5-trimethylbenzene (also known as mesitylene), was studied in atmospheric pressure, counter-flow diffusion flames of ethylene, whose fuel stream was doped with C9H12 isomers, added such that 10%, 20% and 30% of the total carbon was fed as aromatic carbon. In-situ spectroscopy, namely broadband UV-laser induced fluorescence, was used as diagnostic tool to detect combustion-formed nanoparticles whereas laser induced incandescence was used to detect soot particles. Experimental results were compared to those obtained in an ethylene/toluene flame operated in the same conditions in order to highlight the effect of the alkyl chain length and chain branching on particulate formation. The experimental results show that the longer and branched is the side alkyl chain (iso-propylbenzene with respect to n-propylbenzene) the higher is particle formation enhancement. Moreover, increasing the number of methyl groups attached to the aromatic ring (mesitylene compared with xylenes and toluene) does not result in enhanced sooting tendency in the analyzed combustion conditions. (C) 2016 Elsevier Ltd. All rights reserved.