Comparison of Soot Growth and Oxidation in Smoking and Non–Smoking Ethylene Diffusion Flames

Abstract

Abstract A probe sampling technique. which is based on the phenomenon of thermophoresis, is employed to study soot aggregate morphology within a soot emitting (smoking) coannular ethylene/air diffusion flame at atmospheric pressure. Primary particle diameters are obtained through electron microscope analysis of the soot aggregates collected from the flame environment. These observations, when combined with laser diagnostic and particle velocity measurements performed by others, result in the calculation of specific soot surface growth rates, soot surface areas and primary particle number densities along the path line exhibiting the maximum soot volume fraction throughout the growth region of the flame. The above quantities are compared with those measured in a similar non-smoking flame during a separate study. Specific soot oxidation rates are also obtained and compared for the aggregates transported in the upper portion of both flames. The transition from the non-smoking to the smoking behavior with increased fuel flow rate is discussed, in terms of our soot morphological observations in both ethylene diffusion flames.