Characteristics of oxygen-enriched laminar ethylene diffusion sooting flames

This paper reports on an experimental study of the effects of oxygen enrichment on laminar steady ethylene diffusion flames using optical methods. The volumetric concentration of oxygen the oxidizing stream was varied from 21%, i.e. ambient air, to 25.0%, 28.9% and 36.8%, while the volume flow rates of the fuel and the oxidizing stream were held constant with a velocity ratio of 1:6. Soot luminosity in the near infrared, excited hydroxyl radicals (OH*) chemiluminescence, radial distribution of the ground-state OH, soot volume fraction and flame temperature (gaseous) were measured using optical techniques with high spatial resolutions. The experimental methods include direct imaging combined with inversion re-construction, line-wise laser-induced fluorescence, planar laser-induced incandescence and planar two-line atomic laser-induced fluorescence using atomic indium as tracer. Results show that oxygen-enrichment can significantly influence flame structure, soot formation and flame temperature. The datasets, together with those not presented here (including soot particle temperature, primary particle diameter and results in other six flames with oxygen concentration of less than 21%) will help shed light on the role of O2 in soot evolution in flames. The data may also serve as benchmark for developing soot models due to the well-defined boundary conditions, high spatial resolution, systematic nature and combination of measured scalars.