Soot deposition from ethylene/air flames and the role of aromatic intermediates

Abstract

An understanding of the mechanism of soot formation is of importance not only because it is a pollutant but also because it forms deposits in combustion chambers. In the present work soot deposition has been studied using a flat flame, water-cooled, premixed burner burning two rich ethylene/air flames (φ = 2.52, φ = 2.76). Rates of soot deposition for both cooled copper and uncooled stainless steel surfaces were investigated and soot samples from these experiments were analysed for PAH. A quartz microprobe sampling system was used to determine the concentration profiles of aromatic and polyaromatic species in the deposition region. Experimental results support the theory that soot deposition occurs by a thermophoretic mechanism when cooled surfaces are used. It was found that soot deposition rates and associated PAH varied in the flame zone and with the temperature of the cooled plate. If uncooled high temperature surfaces are used then direct surface deposition can take place.