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Comparison of the Flame Characteristics of Circular and Elliptic Jets in a Cross-Flow


 This study was directed to understand the coupling effects of the noncircular geometry of the burner and a cross-flow on the combustion of gas jets. This paper compares the characteristics of propane jet flames from circular (diameter = 0.45 cm) and elliptic (major axis = 0.75 cm, minor axis = 0.26 cm) burners of equivalent exit area in a cross-flow. The elliptic burner was oriented with its major axis or minor axis aligned with the cross-flow. Experiments were conducted in a wind-tunnel provided with optical and probe access and capable of wind speeds up to 12.5 m/s. The burners were fabricated with metal tubes. Instrumentation included a Pt-Pt/13%Rh thermocouple, a quartz-probe gas sampling system, chemiluminescent and non-dispersive infrared analyzers, a video-recorder, and a computer data acquisition system. The measurements consisted of the upper and lower limits of jet velocity for a stable flame, flame configuration, and visible length. Flame structure data including temperature profiles and concentration profiles of CO2, O2, CO, and NO were obtained in a two-zone flame configuration where a planar recirculation exists in the wake of the burner tube followed by an axisymmetric tail. Emission indices of CO and NO were estimated from the composition data. Results indicate that the upper and lower limits of the fuel jet velocity increase with the cross-flow velocity for all burners, and the rate of increase is highest for the elliptic burner with its minor axis aligned with the cross-flow. That burner configuration also produces the longest flame. The emission indices show that the CO production is lower and NO production is higher for elliptic burners than for circular burners in cross-flow. Also, aligning the minor axis of the elliptic burner with the cross-stream is superior in terms of flame stability and emissions of NO and CO.