Combustion Control

Thermoacoustic coupling is an undesired effect that may occur in systems that are driven by confined combustion, such as gas turbine engines, furnaces, boilers, rocket engines, and afterburners. It can lead to a self-excited (combustion) instability, which appears spontaneously in the form of large amplitude pressure and heat release rate oscillations. Such instabilities are hazardous for the apparatus and it is thus desirable to suppress them. Known control attempts assume that the thermoacoustic instabilities correspond to limit cycle oscillations. Therefore, the fact that the thermoacoustic system can undergo bifurcations to more complex nonlinear states, such as chaos is not taken into account, so those methods will fail outright in such a scenario. It is thus a need to improve control/suppression of instabilities.

The method now developed by scientists of TU Berlin offers an active control of chaotic instabilities in combustors whereby a control unit varies the parameters of a dual-stage phase shift module a way that the resulting oscillations in the combustor are reduced to a mono-frequency oscillation with a desired frequency. This method allows transferring the combustion apparatus from the chaotic combustion state into a periodic combustion state, and subsequently into a periodic state with a dominant frequency shifted to the frequency of the desired oscillating state and/or a periodic state with reduced amplitude of oscillations compared to the initial state.