van den Boom J., Lopez I., Schreel K., de Goey L., Nijmeijer H.

Modern gas-fired household boilers have one persistent problem: they tend to make noise. Modern boilers have a high efficiency and make use of ceramic surface burners in order to reduce the emission of NOx. Flat flames stabilized on a surface burner are sensitive to acoustic instabilities. These instabilities originate from an interaction between the combustion and the system in which the burner is mounted. In order to make any further advance in condensing boiler technology this problem has to be solved. Therefore the possibility of active suppression/stabilization of these instabilities is investigated using boundary control. In boundary control the desired objective is achieved by the application of a control mechanism along the border of the system. Two different approaches are possible in this case: introduction of an extra velocity source or modifying the acoustic impedance. For the control synthesis a model-based approach is chosen. The boiler is modeled by deriving the transmission matrix for an open-ended tube with a burner deck at a fixed position. A loudspeaker, used as actuator, will be mounted at the open end of the tube in order to actively change the acoustic impedance. Therefore the dynamics of loudspeaker are also taken into account before control design. A stability analysis based on the complex Eigen values of the system is performed. The obtained knowledge about the damping or amplification of an acoustic instability is used in the control design. The performance of the controller is validated during simulations and experiments. In the experiments the heat released by the flame is used as a sensor in order to investigate if the system is stabilized. Also a comparison is made for stabilization using proportional control.