Effects of turbulent structure and local concentrations on soot formation and combustion in C2H2 diffusion flames

Abstract

The present work is a continuation of previous work to study and model effects of turbulence on soot formation and combustion in turbulent flames. The main objectives have been to investigate effects of turbulent structure and of local chemical and thermodynamic conditions on soot formation and combustion. The following experimental conditions have been investigated for a free jet C₂H₂ diffusion flame: Experimental results are given for mean quantities, fluctuations, the flatness factor and intermittency, and probability density distributions for the soot appearance. Based on a generalized eddy—dissipation concept, predictions were made for all experimental conditions. Variations of the Reynolds number had a strong effect on the amount of soot, with soot concentration increasing as the Reynolds number was reduced. Addition of nitrogen and water vapor to the fuel, as well as preheating the fuel, reduced the amount of soot. These observations could in general be accounted for by the mathematical model, taking into consideration the effects of changes of the turbulent structure due to the various input conditions.