Sooting Correlations for Premixed Flames

Abstract

—Using a Bunsen-type burner in which the name temperature was controlled by nitrogen addition, the tendency of hydrocarbon fuels to form soot has been determined systematically. The effective sooting equivalence ratio reported is based on the stoichiometric relation in which the carbon and hydrogen in the fuel are converted to carbon monoxide and water. respectively, rather than the conventional equivalence ratio or the C/O ratio. The temperature effect is clearly shown by plotting the log of the effective equivalence ratio versus the reciprocal of the (adiabatic) flame temperature, and this dependency is similar for all fuels examined and is relatively weak. At a given flame temperature, an increase in either the number of carbon atoms or the C/H ratio in the fuel molecule increases the tendency to soot. These effects are attributed to the increased pyrolysis rate and the decreased oxidative attack, respectively. No significant effects are found with regard to the structure of the fuel molecule. The sooting tendency at a fixed temperature correlates extremely well with the "number of C-C bonds" or the total C-C bond strength in the molecule.