NANO-ORGANIC CARBON AND SOOT PARTICLE MEASUREMENTS IN A LAMINAR ETHYLENE DIFFUSION FLAME

The formation of carbonaceous particulates in a co-flow laminar diffusion flame has been studied using UV–visible spectroscopy and laser scattering/extinction techniques for measurements of volume fractions and particle sizes. Measurements were performed in a non-smoking ethylene–air flame at atmospheric pressure. UV–visible spectroscopy allowed the identification of two classes of particles: soot particles, which absorb light in the whole spectral range and nano-organic carbon particles (NOC) which are transparent to the visible radiation. The mean size of nano-organic carbon particles was estimated to be about 2–3 nm. This agreed with previous results obtained in rich premixed flames with equivalence ratios across the soot formation threshold. The experimental results indicate that nano-organic carbon particles are formed in the fuel side of the flame front closer to the flame centre line than soot particles and with a concentration level comparable to that of soot. The intermediate spatial location of these particles between the fuel- and soot-containing regions and their high concentration in flame suggest that soot formation is just the consequence of coagulation of NOC particles without a major role of surface growth in the soot loading process.