Experiments on heat content inside a Rijke tube with suppression of thermo-acoustics instability

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.