Characteristics of Soot Formation and Oxidation Regions in Turbulent-Diffusion Flames of Heavy Oils

Abstract

Characteristics of soot formation and burn out processes during combustion of liquid fuels have been presented. Turbulent diffusion flames of heavy fuel oil and its water-emulsion with 10% water were tested. These fuels were equivalent with respect to their thermal parameters in the combustion chamber. Combustion tests were carried out in a large laboratory-scale furnace reproducing practical combustion conditions Samples of soot were collected by a suction probe with water injection. The post-extraction (soxhlet apparatus) carbonaceous residue was classified as soot. It occurred in two forms:

-as individual particles usually joined in simple, short chains,

-as branched clusters of these chains

Soot formation was dominant in the region 0.2-0.4 m from the burner nozzle (the high-temperature combustion zone), slightly shifted from the flame axis, while soot particles growth was fastest strictly at the axis. At a distance over 0.5 m from the burner, soot oxidation predominated. During combustion the presence oT cenospheres was also observed but they occurred mainly in the region beyond the combustion chamber

The particle size distribution was nearly gaussian(up to 0.8 m from the burner), and then it changed into a log-normal distribution. This was attributed to collisions between soot particles and their chains. The size distribution curves of soot aggregates did not match any of the known standard distribution functions. Their character can be explained by the selective decay of aggregates. This mechanism consisted of disintegrating aggregates with the least compact structure into separate fragments which then link with the remaining aggregates.