Experimental Study on Instability Characteristics of Low-Swirl Flames in a Multinozzle Combustor With Different Swirling Arrays

This paper presents experimental study on self-excited combustion instability characteristics of premixed low-swirl flames in a multinozzle can combustor with counterswirl and coswirl arrays. Experiments were carried out over a wide range of inlet velocity from 4 m/s to 15.5 m/s and equivalence ratio from 0.5 to 0.85. Phase-locked OH planar laser-induced fluorescence was employed to measure flame shape and identify heat release rate. Four operation regions: stable combustion region, unstable combustion region, flashback region, and extinguish region are observed for both array burners. The amplitude of pressure fluctuation for counterswirl arrangement is less than the coswirl array, and the stable operating window of the counterswirl array is wider. In the unstable combustion region, the counterswirl flame triggers the 2L mode of the combustion system, while the coswirl flame incites three longitudinal modes with the highest amplitude near 3L. Rayleigh index distribution reveals neighboring flame interaction results in thermoacoustic coupling for multinozzle flames. Additionally, for the counterswirl array, thermoacoustic couplings also exit in the flame base region and shear region while, for the coswirl array, the instability driving zones also locate at the lip region and the tail of center flame which is totally different with counterswirl flame.