Effect of Oxygen Addition to a Near-Sooting Ethene Inverse Diffusion Flame

Abstract

The pyrolysis zone of a near-sooting ethene inverse diffusion flame (IDF, with oxidizer in the central stream) has been probed for temperature and species concentrations. Oxidation processes can play an indirect but significant role on the observed intermediate hydrocarbon species profiles, and therefore on soot formation. Intermediate hydrocarbons can be formed near the main oxidation zone, and diffuse back into the colder fuel-rich region. Acetylene, C4 species (1,3 butadiene, vinylacetylene and diacetylene) and benzene are indicative of ethene pyrolysis and are observed to build up slowly with height. Methane, ethane and C₄ species (allene, propyne and propene) are more indicative of ethene oxidation, and form rapidly low in the flame. The addition of a trace amount of oxygen to the fuel decreased the concentrations of the pyrolytic species and indicates that fuel pyrolysis rates were not enhanced by oxygen addition to the fuel in the present non-sooting flame. However, oxygen addition increased the concentrations of the species associated with oxidation. The relative importance of oxidation and pyrolysis cannot be separated in diffusion flames for fuels which yield similar product distributions from pyrolysis and oxidation experiments.