Experimental study of soot size decrease with pyrolysis temperature rise

Simultaneous measurements of the temperature dependencies of the size, growth rate and relative yield of soot particles were carried out in the shock wave pyrolysis of various carbon-bearing species (carbon suboxide -C3O2, acetylene -C2H2 and benzene -C6H6). In all substances studied in the temperature ranges from 1800-2000 K to 2500-3000 K, a sharp fall in soot size accompanied by a sharp increase in the rate of their formation was observed. Analysis of the data obtained showed that the decrease of soot particle size and decrease in total time of their formation with the temperature rise obey similar exponential dependencies, which could be qualitatively correlated with an increase in the rate of decomposition of the initial carbon bearing molecules. It is established that the observed decrease in the total time of soot particle growth with increased temperature is caused by a decrease in their final size, and the decrease of extinction at 633 nm reflects not a reduction of soot yield, but a decrease in the extinction coefficient upon the reduction of soot particle size. Extinction measurements on a shorter wavelength (220 nm and 248 nm) indicated an approximately constant soot yield in the specified temperature range.