Approaches for Clean Combustion in Gas Turbines by Medhat A. Nemitallah & Ahmed A. Abdelhafez & Mohamed A. Habib

Author:Medhat A. Nemitallah & Ahmed A. Abdelhafez & Mohamed A. Habib
Language: eng
Format: epub
ISBN: 9783030440770
Publisher: Springer International Publishing

Figure 4.19 presents the centerline distribution of the axial velocity component normalized by the value of bulk inlet velocity (5.2 m/s). At all equivalence ratios (with the exception of 0.6), swirl induces an IRZ in the first ~10 cm within the combustor, where the axial velocity is negative indicative of reverse flow or recirculation. The fact that the φ = 0.6 case behaves differently is a clear indication that this case represents the flashback limit, where the flame is most compact, i.e., too small to house a large IRZ, as inferred from Fig. 4.18. Note that the axial velocity reaches +0.9 of the bulk inlet value at Z ≈ 1 cm, and that the centerline temperature peaks at this axial location (Fig. 4.18). Reacting flow thus exists at the centerline, and the bulk inlet velocity prevails within this flow in the absence of IRZ. This infers that a delicate balance exists at the burner throat between the bulk velocity and flame speed before the onset of flashback if φ were increased. This balance was discussed in an earlier study by the authors [67], where it was concluded that the combustor flashback limit occurred consistently at a constant flame speed of 5.2 m/s within the examined φ-O.F. space, because the bulk inlet velocity was fixed at 5.2 m/s. The upcoming analysis of flame structure will shed more light on the limiting flashback case.

Fig. 4.19Centerline distribution of the axial velocity component normalized by the value of bulk inlet velocity (5.2 m/s) at different equivalence ratios

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