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Show conserve space and facilitate clarity within the charts. The open and closed triangles represent the low and high excess air conditions, respectively, in Figure 9. DISCUSSION t::,. .... ex-swirl 5% S'=0.72 @ ® ~ ... radial 5°1o S'=0.62 ~ ... ex-swirl 5°1o S'=0.92 ® .. _ ex-swirl 20% S'=0.66 (J) @ .... radial 15°10 S'=0.62 4 co-swirl 5°1o S'=0.40 CD ~¥ • .-- co-swirl 200/0 S'=0.52 ® Low Excess Air High Excess Air I I I I I I I I 1% 2% 3% 4% 5% 6% 7% 8% 9% Recirculated Mass (0/0) Figure 9: NOx vs. Recirculated Mass (CD Denotes condition identified in Table 2) The recirculated mass provides an index of actual (versus input or geometric) swirl strength. The geometric swirl strength, S', reported in Figure 7 is the projected swirl strength based on the proportion of swirl to total air mass flows in the combustion air plenum (Equation 1). Each of the fuel injectors affect the actual swirl strength that emanates into the burner. The co-swirl injector reinforces the swirl while the radial and counter-swirl injectors increasingly degrade the swirl strength. Laser anemometry data are required, as a result, to establish the actual swirl strength. Assuming the stronger the swirl, the higher the recirculated mass, then the recirculated mass can serve as an index of swirl strength. Figure 9 shows, in fact, that the co-swirl injector yields the highest recirculated mass, while the counter-swirl injector yields the lowest recirculated mass. The radial injector falls in between but is closer to the swirl strength of the counter-swirl injector. Note that the radial injector at 5% excess air and S'::{).62 (condition 3) has the same recirculated mass as the counter-swirl injector at 5% excess air and S'=O.92 (condition 6). The explanation is that the stronger input swirl strength (S'=O.92) of the counter-swirl injector is off-set by the higher degradation of the swirl caused by the fuel injection relative to the radial injector. 11 |