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Show 3 The up-fired, coaxial, natural gas burner consists of four elements: the entry plenum, swirler, contraction, and quarl. The central natural gas fuel tube has a 0.5 inch diameter and is surrounded by a 1.0 inch combustion air annulus. Swirl is introduced into the air annulus via an axial stream and a tangential, or swirl, air stream. With this arrangement, the swirl intensity can be varied by changing the ratio of swirl air to axial air. For these experiments, clockwise swirl is used, and the swirl intensity, Sf, is represented as the square of the swirl air flow divided by the total air flow, Sf- ( m¢ J2 ma+ m; (1) This definition is similar to the geometric swirl number defined by Feikema, et al., (1990): where 1C • r . d ( mAl J2 S - 0 a 'r g- 2Ar ma +mt/J r 0 = radius to tangential swirl inlet da = throat diameter At = total area of tangential swirl inlets rna = axial air mass flow rate mt/J = tangential air mass flow rate (2) As such, Sf can be converted to the geometric swirl number by multiplying by a constant geometric factor, which is 3 for this burner. The fuel injector designs are based on rapid mixing strategies, namely the radial injection of free jets into a high velocity cross-stream. As shown in Figure 2, three variations of radial jets are considered: 1) straight radial jets, 2) co-swirling radial jets, and 3) counter-swirling radial jets. The fuel swirl is accomplished using radial jets tangential to the inner diameter of the nozzle. The "co-swirling" and "counter-swirling" labels refer to the orientation of the radial jets in relation to the swirling air. Section A-A Section A-A Section A-A i i i A A Counter-Swirl Radial Jets Co-Swirl Figure 2: Fuel Nozzles Investigated |