Combustion instability analysis of pilot flame in model combustor

To address he combustion instability of pilot flame in the model combustor, the multi-point dynamic pressure and flame images are experimentally measured in the combustor, and analyzed by means of fast Fourier analysis and proper orthogonal decomposition(POD). It is observed that with the increase of the equivalence ratio, two bifurcations occur with limit cycle oscillations, and the corresponding unstable modes correspond to the third-order and second-order intrinsic longitudinal acoustic modes of the system. The POD results show that the vortex-acoustic frequency lock-in occurs at the longitudinal acoustic mode frequency of the combustor, and the acoustic-vortex-flame coupling instability process occurs in the combustor. On the one hand, large-scale vortex shedding increases sound energy output by altering the flame area and producing severe oscillations in heat release with an increase in equivalency ratio. Conversely, as the angle between two flame branches increases, the main wave direction of the flame position is along the same axis as the main acoustic wave. The modal transition takes place when two factors come into play: the thermoacoustic coupling becomes easier, and the phase angle of the pressure pulsation and heat release pulsation coupling lowers. © 2024 Beijing University of Aeronautics and Astronautics (BUAA). All rights reserved.