Characterizing nonlinear interaction between a premixed swirling flame and acoustics: Heat-driven acoustic mode switching and triggering

The aim of this present study is to examine the critical role of air-fuel equivalence ratio Ф and air flow rate on triggering self-excited thermoacoustic oscillations in a swirling combustor, which is widely applied in industry to achieve low combustion emissions. For this, experimental study of the effect of air-fuel equivalence ratio in a propane-burnt swirling combustor is conducted to gain insights on the nonlinear dynamics behaviors of the thermoacoustic oscillations. A series experiments are conducted by varying 1) the air flow rate and 2) the equivalence ratio. It is found that the air flow rate and the equivalence ratio play important roles on producing limit cycle thermoacoustic oscillations. The frequencies and amplitudes of these oscillations strongly depend on the equivalence ratio. In addition, the dominant thermoacoustic mode is found to switch from a higher frequency at ω3 to a lower one at ω1 for a given Φ, as the air flow rate Qa is varied. However, as Qa is set to a given value, increasing the equivalence ratio from 0.8 to 1.2 leads to the dominant frequency being shifted by approximately 20%. In general, the present study sheds lights on the nonlinear characteristics and behaviors of heat-driven acoustic oscillations in a swirling thermoacoustic system.