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Show E 139~====~===-----~~--~----~~----~1 E Temperature (OF) - 99 Q) ..s--.,. o C ~ 59 CJ) is ~ 19~~UU~~~~~~~ww~~~~~~~~~~w ~ 40 80 120 160 200 240 280 320 360 400 440 480 520 Radial Distance from the Burner Center Line (mm) Figure 12. Isothermal contour plots of the in-flame gas temperatures for the Flame 3 condition. Flame 3 is operated with high levels of airdiluent through the secondary injector. The secondary gas to fuel volume ratio is 2.6:1. Other burner process variables are operated at baseline conditions. Baseline In-Flame Gas Composition Measurements: The baseline flame composition (Flame 1) is characterized by the in-flame gas composition plots presented in Figure 13. The plots show that higher NO concentration regions (Figure 13 (a» are closely related to the higher concentration of hydrocarbons (Figure 13 (b» and carbon monoxide (Figure 13 (c». High hydrocarbon and carbon monoxide (CO) concentrations indicate regions of continuing or incomplete combustion. The oxygen (02) concentrations (Figure 13 (d» also indicate that the combustion gases in the outer flame zone near 500 mm approaches a fuel rich condition. This is indicative of the staging combustion mechanism in which the primary air stream is slowly entrained into the secondary jets a considerable distance from the burner. Jet Mixin& and Combustion Studies of Complex Flame Structures: Mie scattering photographic images provided valuable information on the mixing of the secondary and primary jets. This information provided information on the large scale pattern of jet behavior. These images, which are not photo-reproducible for this paper, are useful in identifying flame fronts by observing low density seeding which is indicative of the gas expansion of the flame fronts. The overall paths of . the burner jets can be depicted from the velocity data. Figure 14 illustrates, for the baseline flame condition (Flame 1), the gas paths and velocities along the secondary jet path. The path of the secondary jet and primary stream are seen to begin merging about 130 mm (5 inches) from the burner centerline. The four secondary jets have a jet-in-cross-flow characteristic as described by M.A. Field, et. ale [10]. . The qualitative ·CH concentrations of Flame 1 captured by chemiluminescence techniques on photographic images, which are not reproducible for this paper, showed the secondary jet in combustion along the lower half circumference of jet. This indicated, and follows logically, that most entrainment of oxidant by the secondary jets occurs along the lower portion of the jet where oxygen is in abundance from the secondary and tertiary air supply. The high ·CH radical concentrations are present beginning at about 300 rom (12 inches) from the burner. This infonnation confinns that the secondary jet and primary stream begin mixing shortly upstream and initial combustion reactions occur a few milliseconds later. Preliminary calculations indicate that between the. initial secondary jet and primary stream mixing location at 130 nun (5 inches) to the initial location of high ·CH radical concentrations at 300 mm (12 inches), the jet travels the 170 mm in approximately 14 milliseconds at an average speed of approximately 12 mls (40 ftJs). This suggests that combustion is rapid once mixing is achieved which stresses the importance of mixing in delaying combustion. 11 |
