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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. [ABSTRACT FROM AUTHOR]

Silencer is a device mainly used for attenuation of the engine exhaust noise. Several modifications were attempted to improve the performance of a silencer. In this paper experimental and simulation study was carried out to determine the effect of radial air injection on the temperature and sound pressure level. The radial air injection is introduced in the form of jets inside the silencer. The design of available silencer was studied, and the 3D model was prepared using CATIA software. Simulation study was carried out using ANSYS Fluent, to determine the temperature distribution inside the silencer with and without modification. The radial jets at different pressure were introduced inside the silencer at three different locations. To acquire sound pressure level and temperatures at different locations, Lab View software and FFT analyser were used. The performance of silencer is analysed by comparing temperature of exhaust gases and sound pressure level at constant speed of 3000 rpm. With radial air jets of 2 bar reservoir pressure at three different location Overall Sound Pressure Level reduces by 6 dB and 42 K reduction in temperature of exhaust gases. [ABSTRACT FROM AUTHOR]

The present work describes the occurrence of thermo-acoustic instability inside a horizontal Rijke tube and its suppression using an open loop active control technique. The Rijke tube is provided with a co-axial pre-mixed gas burner as the source of heat, which could be placed at any desired position. Radial injection of air (less than 3% of the total mass flow) through micro-jets into the flame is used as a control technique to suppress the thermo-acoustic instability. The rise in heat content inside the Rijke tube, estimated from the temperature mapping, clearly shows reduction in the heat loss as a result of complete suppression of the thermo-acoustic instability. However, the stability achieved passively by means of a slight shift in the burner position does not result in any change in the heat content. There is a visible change in the appearance of the burner flame when the above two methods are used to suppress the thermo-acoustic instability. The flame is seen to significantly shrink in length and spread radially when the control technique was applied. The flame dynamics is believed to determine the heat loss and hence the heat content inside the Rijke tube. [ABSTRACT FROM AUTHOR]