Acoustic Detection of Imminent Blowout in Pilot and Swirl Stabilized Combustors

This paper describes an experimental effort to characterize the acoustic emissions of lean, premixed combustors operating near blowout conditions. Its objective is to use measurements of the flame’s acoustic signature to determine the proximity of the combustor to incipient blowout. The feasibility of the method was performed on two combustors with fundamentally different flame holding methods: externally anchored pilot and swirl-stabilized. Acoustic measurements indicate that the low frequency spectrum exhibits a strong dependence upon the degree of flame stabilization. High speed intensified camera images of the flame were also taken to get a better understanding of the unsteady flame dynamics. In the piloted burner, it became visibly obvious that the flame was approaching blowoff by increased flickering, unsteadiness, and non-symmetric flame attachment. The results from the swirl burner, however, show that the blow-off transient was characterized by short duration, localized extinction and re-ignition events. These events increase in frequency and duration as blowout is approached. Several data analysis approaches using spectral, statistical and wavelet techniques with varying degrees of sensitivity are shown to be capable of detecting precursors to blowout for both burners.