Experimental study on quantitative radiation properties of laminar oxygen-enriched inverse diffusion flames in gas turbines

In gas turbines, inverse diffusion flames form when film-cooling air reacts with fuel-rich packets from the combustor. Investigations have focused on the quantitative radiation heat transfer in oxygen-enriched inverse diffusion flames (IDFs) since it plays an important role not only in fundamental combustion research, but also in much research on industry combustion, such as gas-turbine engines. To investigate the quantitative radiation properties of oxygen-enriched IDFs, a midinfrared thermal camera coupled with two different band-pass filters was selected to acquire the thermal radiation intensity of carbon dioxide and soot. The oxygen mole fraction in the oxidizer was varied from 21% to 100% using a co-flowing inverse flame burner to produce steady flames. The radiation intensities from carbon dioxide are approximately 15 to 20 times stronger than those from soot with different oxygen enrichment in IDFs. Both radiation from carbon dioxide and soot increased as the oxygen index of the oxidizer was increased, and the increase in radiation from carbon dioxide was more drastic than that from soot when the oxidizer was more enriched. However, the growth rate of the maximum radiation emission from carbon dioxide along the flame centerline decreased when the oxygen index of the oxidizer exceeded 80%. Furthermore, a second peak appeared along the flame centerline in the radiation curves from soot when the oxygen index of the oxidizer exceeded 40%. The axial position of the second peak was closer to the burner exit than that of the first peak. Moreover, the values of the second peak presented a steeper growth rate than the first one with greater oxygen enrichment.