Investigation on the intrinsic thermoacoustic instability of a lean-premixed swirl combustor with an acoustic liner

In the present work, the combustion instability of a premixed swirl combustor was experimentally and theoretically investigated. Results show that both intrinsic thermoacoustic (ITA) mode and cavity acoustic mode can dominate the instabilities of the combustor. For higher equivalence ratios, the ITA mode, the frequency of which is insensitive to the length of the combustion chamber, is more prone to instability than the cavity mode. The addition of an acoustic liner with bias flow was found to be effective in suppressing the combustion oscillations for the cavity acoustic mode, but not for the ITA mode; in contrast, the ITA instability can be triggered or even enhanced by increasing the bias flow Mach number. By measuring the flame transfer functions (FTF) of both self-excited and external-forced modes, it was found that the FTF phase of the ITA mode under self-excitation is close to -p, which is quite different from that of the quarter-wave mode.