Combustion driven oscillations

Abstract Combustion driven oscillations can occur when a turbulent flame is enclosed in a tube or cavity. Interaction between heat fluctuations and the internal standing wave field at one of the natural frequencies of the air column produces strong organ pipe tones. The sound power emitted by this thermal-acoustic interaction depends on the impedance either side of the combustion zone and on a transfer function defining the response of the flame to sound wave disturbances. If this power exceeds the rate at which energy is dissipated at the cavity boundaries then there is a growth of the internal pressure field and an increase in the radiated sound. Plane wave theory is used to calculate the flame transfer function and adjacent impedances for a simple gas fired tube assembly. The predicted instability frequencies are then compared with experimental data. The results indicate that the flame transfer function plays a dominant role in determining the acoustic stability of the cavity and that insufficient data is available for accurately predicting unsteady flame front behaviour.