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Show DISCUSSION For the counter-swirl injector and radial injectors, a high concentration fuel "ring" or ridge forms along the outer annulus wall. This impingement causes the fuel to spread circumferentially in the vicinity of the outer wall. The co-swirl jet, on the other hand, does not impinge on the annulus wall; the fuel jet remains coherent, and mixing can only occur at the periphery of the jet due to the velocity difference between the jet and the swirling air flow. This difference in mixing behavior is held responsible for the lower perfonnance for the co-swirl injector. Indeed, the condition corresponding to the best perfonnance is the counter-swirl injector at 20% excess air and S'=0.66 (condition ®), which has a fairly uniform fuel ring along the outer annulus wall. The high fuel concentration occurs at the outer annulus wall. These regions evolve in the burner quarl to form the flame petals evidenced downstream. For the counter-swirl and radial injectors, the flame petals are connected; this is hypothesized to be due to the evolution of the fuel rich ring that forms along the outer annulus wall at the burner throat. The fuel ring and large, undulating pockets of fuel may serve as ignition and reaction zone sites which enhance stability due to their large spatial distribution. The cases with the undulating pockets of fuel (conditions @, @, and @) are indeed more stable and have higher NOx emissIons (see Table 1 and Figure 2). SUMMARY Measurements • The velocity measurements of the simulated burner throat show the location of and disruption caused by the fuel jets on the swirling air flow. • The axial and tangential velocity profiles are used as input boundary conditions to the modeling. Modeling • Using the simple, 3-dimensional geometry, non-reacting cases of the six conditions outlined in Table 1 were modeled. • The modeling results show the same general trends as the planar measurements of axial velocity, with alternating regions of high and low velocity due to the momentum transfer between the fuel jet and the swirling air. • The counter-swirl and radial injectors impinge on the outer annulus wall, forming a "ring" of fuel and air circumferentially mixed along the wall. The higher spatial distribution of the fuel 11 |
