Growth rate of soot particles

Although there have been many studies of soot formation, the processes involved are still not fully understood. Recently, particular attention has been directed at the rate of growth of soot particles when rich premixed hydrocarbon-oxygen mixtures are burned in a flat flame, but an alternative approach is to compare the reported growth rates for soot particles in flames with those predicted from the rate constants for pyrocarbon growth in the absence of soot nucleation. In this paper it is shown that in the absence of soot formation there is no difference in the growth processes of soot particles and pyrocarbon. The observed discrepancy in the growth rate constants for a soot surface and a quartz filaments (4.5 times for methane and 2-3 times for other hydrocarbons) results from the appearance of a rough surface on the quartz. It is known that when soot is formed in the course of methane pyrolysis, the growth rate of particles is two order higher than the pyrocarbon growth rate in the absence of soot formation, and the same effect has been observed with other hydrocarbons. This acceleration in the soot particle growth at low hydrocarbon concentration is caused by destruction of hydrocarbon radicals onmore » the growing surface. Acceleration of pyrocarbon growth in the thermal decomposition of methane, acetylene, and benzene is also found at temperatures up to 1400{degrees} C in pipes of 1 mm diameter, and soot formation is prevented with the rate of gas flows of 100 ms{sup {minus}1}. The present calculations were made for typical mixtures compositions in premixed sooting flames for which detailed data on the growth of soot particles has been presented.« less