Acoustic detection of blowout in premixed flames

Work to develop a practical, fast diagnostic technique to monitor the proximity of a combustor to blowout using measurements of the flame's acoustic signature is described. The feasibility of this approach was demonstrated on three combustors with different flame holding mechanisms that are used in most practical combustion devices: pilot, swirl, and bluff-body stabilized flames. Extensive high-speed flame images were obtained and analyzed in conjunction with simultaneous acoustic data. These analyses revealed changes in the low-frequency spectrum and/or the increased presence of time-localized and intermittent events in the acoustic data as the combustor approached blowout. Based on these observations, spectral, statistical, wavelet, and thresholding signal-processing schemes were developed for detecting blowout precursors with varying levels of time response, sensitivity, and robustness.