Active suppression of swirl-stabilized combustion instability

In this paper, active suppression methods are studied to reduce combustion instability. In particular, a controller is used to output a control signal to a sampled oscillating pressure wave. A control acoustic wave is released from an actuator in opposite phase to the oscillating pressure wave. The two waves superimpose and reduce the oscillating intensity of combustion instability. The experiments suggest that the oscillating pressure presents mutagenicity in combustion instability conditions: the frequency, amplitude, and phase will change suddenly. Moreover, the flame pulsation will also follow the control acoustic wave. Therefore, the output control phase should have a higher refresh frequency. As the novelty of this paper, two methods of phase following/recognition based on FPGA are proposed to suppress oscillating pressure: Sinusoidal approximation and waveform delay, respectively. The former is responsible for identifying the initial phase of the oscillating pressure according to the sampling data every 25 ms, whereas the latter is responsible for suppressing future oscillating pressure by the waveform acquired in the previous period. The results suggest that the amplitude of the oscillating pressure can be reduced by more than 50% under different working conditions. Moreover, proper orthogonal decomposition and dynamic mode decomposition are used to study the suppression effects on the intensity of flame pulsation. The ability of active control in suppressing flame fluctuations is relatively limited.