Mitigation of premixed flame-sustained thermoacoustic oscillations using an electrical heater

To stabilize unstable combustion systems in gas turbines, aero-engines, rocket motors, boilers and furnaces, there is a need to develop a simple but applicable mitigation/control strategy. The present work considers using an electrical heater to mitigate limit cycle thermoacoustic oscillations sustained by a premixed flame. For this, nonlinear recurrence relation analysis of the thermoacoustic system with the premixed flame and an electrical heater confined is conducted first. It is shown that the heater placed at a proper location results in significant damping on the thermoacoustic oscillations. Experimental measurements are then performed. It shows that the heater can dampen thermoacoustic oscillations, depending strongly on (1) its location and (2) its output electrical power. The minimum electrical power Q min s is determined and compared for four different axial locations. The optimum position x opt s at which the heater is most effective in damping combustion-excited limit cycle oscillations is shown to be at 0.72 ⩽ x s / L ⩽ 0.75 for the eigenmode with frequency ω 1 / 2 π ≈ 240 Hz. This finding agrees well with those from the energy exchange analyses via linearized flame and heater models. It is also experimentally shown that sound pressure level is reduced by 70 dB, as the heater is placed at x opt s and its output power is increased to 218.2 W. Furthermore, the thermoacoustic mode frequencies are found to be increased with the limit cycle oscillating being dampened. The successful experimental demonstration opens up another possible way to mitigate/control thermoacoustic oscillations using an electrical heater.