Experimental Investigation of Oxygen-Enriched Lifted and Attached Turbulent Diffusion Flames

Abstract

The interactions between turbulent fluid flow and chemical kinetics are examined experimentally in attached and lifted turbulent oxygen-enriched gaseous non-premixed flames by firing a methane jet vertically into a co-flowing oxidant shroud. Stable species, including nitrogen oxides, were measured using physical-probing techniques. Hydroxyl radical concentrations were monitored using laser-induced fluorescence (LIF). The level of oxygen enrichment in the shroud air was varied from 21% to 28% while maintaining constant average fuel-nozzle velocity and Reynolds number. Within the operating range, attached as well as lifted flames were observed. Physical and chemical differences in structure between attached and lifted flames are presented. With an increasing degree of oxygen, enrichment flames become shorter and more luminous in appearance. Attached flames appear more luminous with longer flame lengths. Significant amounts of oxygen were found on the fuel-rich side of the stoichiometric envelope in lifted flames, underscoring partially premixed characteristics near downstream locations.