Effect of position of radial air injection plane on control of thermo-acoustic instability using active closed-loop method

Abstract

Thermo-acoustic instability occurs when self-excited oscillations are generated due to the coupling between unsteady heat release and acoustics. This phenomenon can result in an increased rate of vibration, structural damage, and produces unwanted emissions. Thermo-acoustic instability occurs in rocket engines, gas turbines, combustors, and furnaces. When thermo-acoustic instability occurs, many modes are developed naturally at a specific point. Some waves are unstable and some are stable. So, to study this phenomenon the most unstable waves are considered and a technique is developed to suppress these unstable waves. A radial air injector as a closed-loop active control method is used for breaking the coupling between the heat waves and acoustics inside the 1D combustion chamber. The distance between the burner and the air injector is varied for the fixed position of the burner with respect to the Rijke tube, that is, x/L = 0.01125, 0.0075, and 0.00375. This closed-loop method works based on the feedback acquired from a microphone. The control method is built using DAQ and Arduino with the LabVIEW as interface for Arduino (LIFA). An air flow rate controller setup is developed to control and measure air required for suppressing the thermo-acoustic instability. Thermo-acoustic instability is effectively suppressed with the help of radial injection in the form of micro-jets at the downstream of the burner as the closed-loop controlling method. It is concluded that when the radial micro-jet air injection plane is closer to the burner head, the thermo-acoustic instability gets suppressed in a short time and with a lesser quantity of air.

Development of closed-loop active control method for suppression of thermoacoustic instability using radial air micro-jets

“…Active control can be implemented by two ways, namely open loop and closed loop. Different controllers in active control methods include external acoustic dampeners (loudspeakers) [22] , fuel modulation (phase-shifting controller) [22] , secondary fuel injection [23] , [24] , [25] , releasing air radially inside the combustor (radial air injection system) [26] , [27] , [28] , [29] . The radial jets can be used as open loop method to break the coupling and suppress the thermoacoustic instability [7 , 13 , 28] .…”