Experimental demonstration of mitigating self-excited combustion oscillations using an electrical heater

The present work considers mitigating combustion instability occurred in a conventional Rijke-type combustor and a Y-shaped one. For this, theoretical, numerical and experimental studies are conducted to shed lights on the role of applying a heater on suppressing flame-exited oscillations. Theoretical modal analysis shows that the heater acts like an acoustic absorber. Further 2D numerical investigations are conducted on a Rijke-type combustor, in which a propane-fuelled flame and heating bands with constant surface temperatures are implemented at upstream and downstream of the combustor. Limit cycle oscillations produced by the flame are found to be significantly suppressed, if the surface temperature of the heating bands is large enough. Experimental study is then performed on a Rijke tube, in which implementing a heater leads to the unstable combustion system being successfully stabilized. Further validation of the proposed control approach is performed by implementing the electrical heater in an upper branch of a Y-shaped combustor. A premixed propane-fuelled flame is enclosed in the bottom stem. When the heater is not actuated, self-excited thermoacoustic oscillations are generated at approximately 190 Hz. However, with the heater being actuated, sound pressure level is successfully reduced from 130 dB to 80 dB. The present work opens up an alternative but practical control approach to enable combustors being operated stably.