Macrostructure and NO_x emission evolution characteristics of lean‐premixed flames under combustion instability

Abstract

Effects of combustion instability on flame macrostructures and NO x emissions were conducted experimentally in a model gas turbine combustor. Two variables of the CH 4 flame were investigated-the flow rate and the equivalence ratio. Results indicate that flame macrostructure changes when the equivalence ratio increases from 0.50 to 1.00, the average total length of flame front firstly decreases from 105 to 75 mm, and then increases to 110 mm. While the average length of flame root decreases from 25 to 5 mm. The appearance of the flame front evolves from a "M" shape to a reversed "V" shape, but the appearance of the flame root changes from elongated V shape to a flatted V shape. The envelop diagram of different combustion instability signifies that there are mode shifting of flame-acoustic interactions in the combustion chamber. Under instability conditions, the temperature and velocity distribution of the flame front or flame root affects the NO x emissions. Along the radial direction, the peak temperature in the inner recirculation region and the outer recirculation region drops. This article explored the dynamic characteristics of lean-premixed flames under combustion instability, which could be instructive to the designing of stable and clean combustors in industrial gas turbines.

Effect of carbon dioxide, argon, and helium jets on the synchronous control of combustion instability and NOx emission

“…With the geometry parameters provided in Table 1, the cut‐off frequency of the lean‐premixed combustor can be calculated as 1510 Hz 19,20,29 ; this value was larger than the self‐excitation frequency (264 Hz) of the unsteady flame in this study. Thus, the acoustic pressure in the combustion chamber can be treated as one‐dimensional 29 . The self‐excited oscillation sound pressure amplitude was determined by the fast Fourier transform (FFT) analysis.…”

“…This research was carried on a model gas turbine combustor, which was used for lean‐premixed combustion 19,20,29 . Figure 1 shows the detailed structure of the model gas turbine combustor.…”

“…The inner diameter of these four parts is keep constant as 114 mm. At the inlet of the lean‐premixed combustor, a loudspeaker flange interface was retained 20,29 ; the height and diameter of the flange interface are 202 and 200 mm, respectively. The four parts of the combustor were connected with flanges.…”

“…The narrow holes in the honeycomb are 5 mm, and the minor gaps in the corrugated plate are 4 mm. In Figure 1, there are 16 vanes in the axial swirler; the angle of the vane is 60° 19,20,29 . The height of the burner swirler is 100 mm.…”

“…Figure 3 shows the 3‐D section image of the combustor in Figure 1. The top view, front view, and oblique view of the combustor were demonstrated 19,20,29 . Four holes near the bottom of the burner were used for tabular injector installation.…”