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Show FUEL INJECTORS The fuel is injected 0.25" upstream of the burner throat via the three injectors shown in crosssection in Figure 5. Air Swirl Air Swirl Air Swirl a o a Section A-A Section A-A Section A-A Co-Swirl Radial Counter-Swirl Figure 5: Fuel Injectors The fuel injection strategy is designed to provide rapid mixing upstream of the reaction to promote "premixed" performance without the operational safety issues and added infrastructure typically associated with premixed systems. To accomplish the rapid mixing, the fuel is injected 9(f to the air cross-flow (Le., into an annular, swirling air channel), upstream of the burner expansion plane, where air velocities are relatively high, the mixing channel is relatively restricted, and reaction is likely to be precluded. The co-swirl fuel injector introduces the natural gas with a swirl component that coincides with the annular air swirl. The radial fuel injector locally (Le., near the injector face) "opposes" the annular air stream due to the induced velocity shear. This both "agitates" the fuel and air interaction, thereby promoting fuel and air mixing in the near field, and locally "disrupts" the swirl, thereby degrading the strength of the swirling air. The counter-swirl fuel injector is even more "disruptive" by introducing the natural gas with a swirl component that directly opposes the annular air swirl. As a result, for a given load (Le., overall fuel flow rate), the mixing of the natural gas and combustion air can be systematically varied. 5 |