Abstract
The flame structure and dynamic response of stratified swirl flames are investigated using a stratified premixed swirl burner. The change of swirl intensity is achieved by swirlers with different swirl angles. Stratification of the flow and mixtures is established by varying the bulk air flow rates and mixture equivalence ratios between the inner and outer annulus. Depending on operating conditions, four different flame structures are stabilized in the combustor: A V-shaped flame (V-flame), a stratified flame (S-flame), a lifted flame (L-flame) and a special plate-shaped flame (P-flame). Thermoacoustic instabilities are then investigated. Generally, the frequency and intensity of the pressure and heat release pulsation are coupled. The amplitude of the pressure and heat release pulsation are all sensitive to the swirl intensity, air split ratio (ASR) and stratification ratio (SR). Large amplitude limit cycles are found in the strong swirl, high ASR and high SR flame. The dominant frequency of pulsation is about 100 Hz in the cases with SR < 1, when SR > 1, the dominant frequency fluctuates between 400 Hz and 500 Hz. The hysteresis phenomenon is also observed in current experiments. Different flame structures can occur in the same operating condition by varying the operating routines.
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