Infrared measurements of thermoacoustic instabilities in a swirl-stabilized combustor

An experimental study of the pressure and temperature fluctuations associated with thermoacoustic instabilities was performed on a 30-kW model gas turbine combustor. The combustor consists of an annular swirling air stream with a centrally located Parker Hannifin Research Simplex Atomizer that injects liquid fuel ( ethanol) into a dump combustion chamber. A high-speed infrared (IR) imaging system was used to qualitatively visualize the fluctuations in the CO2 thermal emissions ( temperature) within the combustor. The IR measurements were acquired in conjunction with pressure measurements obtained from high-frequency response transducers to investigate the coupling between the thermal and acoustic fields. The IR visualizations showed that near the flame blowout regime, which corresponded to the higher-pressure oscillations in the combustor, the flame was compact and fluctuated at the instability frequency near the combustor dump plane. The effects of phase-delay active control on attenuating the instabilities were also studied using the IR imaging system. With phase-delay control, the magnitude of the temperature and pressure fluctuations was reduced. Time-averaged IR measurements also showed higher average temperatures and stronger temperature gradients near the base of the flame with phase-delay control.