Mobility size distributions of soot in premixed propene flames

The evolution of mobility particle size distribution function (PSDF) for premixed propene flame soot was investigated in the burner stabilized stagnation (BSS) flame configuration. The measurements were carried out for two series of flames with the equivalence ratio equal to 1.8 and 2.07, as a function of the burner-to-stagnation surface separation distance. The flame temperature was varied from 1820 to 1940 K in each series to examine flame temperature effects on the measured PSDF in a systematic manner. Measurements were compared to those determined previously for ethylene flames. Qualitatively, bimodal PSDFs were observed in all propene flames. Like the ethylene flames studied previously, the mobility diameter at the trough of the bimodal distribution and the median mobility diameter of the large size lognormal mode both shift towards smaller particle size as the flame temperature increases. Quantitatively, soot nucleates and grows in propene flames earlier and faster than in ethylene flames under comparable conditions. In particular, the propene flames produce a substantially higher number of soot nuclei than in the ethylene flames. The observations made for the propene flames and the comparison with ethylene flames strongly indicate that detailed soot formation processes, such as the PSDF, can be extremely sensitive to parent fuel structure in premixed flames.