Heat release rate response of azimuthal thermoacoustic instabilities in a pressurized annular combustor with methane/hydrogen flames

Assessment of the LES-FGM framework for capturing stable and unstable modes in a hydrogen / methane fuelled premixed combustor

“…This has the consequence of a small 'kink' in the pressure fluctuation for Case U1 in Figure 7, which looks like a secondary minor maxima and minima in the p ′ wave. This may be due to different parts of the flame driving the pressure fluctuations at different harmonic frequencies; Ahn et al [32] showed that for Case U1, the transverse oscillations of the flame is in sync with the fundamental frequency and drives the pressure oscillation at this frequency, while for the first harmonic it is instead driven by asymmetric heat release rate between the left and right sides of the flame.…”

“…The phase difference between the fluctuations of Q and p ′ can also significantly affect the limit cycle. Cases with smaller phase differences can cause larger limit cycle amplitudes since the forcing mechanism are more in sync with the pressure waves [32].…”

“…The mode amplitude at 25% hydrogen by volume is larger than at 43% hydrogen by volume. High speed imaging of OH* chemiluminescence revealed that the heat release rate response of a higher hydrogen content case is out of phase with the pressure oscillations, which results in an overall lower amplitude [32].…”