Experimental study on thermoacoustic instability and emission characteristics of premixed swirl flame in a longitudinal combustor

To investigate thermoacoustic instability and emission characteristics in premixed swirl combustor, several lowemission swirlers with different vane stagger angles were designed. At normal temperatures and pressures, the flow field, flame shape, thermoacoustic instability and emissions as well as their relationships were investigated. The flame shapes and swirling flow dynamics were characterized by chemiluminescence (CL) imaging and particle image velocimetry (PIV), the pressure oscillations and emissions were obtained using microphone and flue gas analyzer. The results indicate that the position and size of recirculation zone varies abruptly with the swirl number. When combustion equivalence ratio is 0.8-1.5, three flame modes, including attached flame, Wshape and V-shape detached flame, arise above the combustor as equivalence ratio is reduced. The V-shape detached flame shows the weakest sound pressure, which suggests the best stability and lowest emissions. Additionally, emissions are also affected by swirling intensity. In general, the inside stage of swirler with higher swirling intensity generates lower NOx emission. For the two-stage swirler C3, the maximum CO and NOx emissions are about 2 ppm and 40 ppm respectively. In the same flame conditions, the three-stage swirler C5 has a lower NOx emission, less than 8 ppm.

Automated summary

The swirl number significantly affects the position and size of the recirculation zone; reducing the combustion equivalence ratio can generate different flame modes; the V-shaped detached flame exhibits the lowest sound pressure, best stability, and lowest emissions; emissions are also influenced by the swirling intensity.