Combined applications of analytic methods for detection of combustion instability triggering

Analytic methods are applied to investigate the dynamic behaviors of the model chambers with different lengths. They are dynamic mode decomposition (DMD), short-time Fourier transform (STFT), and recurrence plots (RPs), which are applied simultaneously to the chambers. The DMD can extract the dynamic modes in the chamber, their frequencies, and their growth rates, but can't find when the dynamic modes appear. Accordingly, the STFT is conducted to find the initiation of acoustic oscillations with specific frequencies and their evolution in real-time. Recurrence plots (RPs) are applied to see phase synchronization between oscillations of pressure and heat release rate and thereby, the triggering time of resonance is determined. In this study, the three methods are applied to the two model chambers, which are devised intentionally for stable and unstable combustion, respectively. The results showed that the present approach could extract unique stability characteristics in each chamber devised in terms of combustion instability. The combined applications can provide complete information on dynamic behaviors, including resonant frequencies, acoustic modes, sustainability of oscillations, the onset of instability triggering.