Combustion instability arises due to an interaction between combustion and acoustic waves.
Essentially the sound waves perturb the flame, whilst the unsteady combustion generates yet more sound. The phase relationship between the rate of heat release and the acoustic waves is crucially important. It not only affects the energetics, influencing whether disturbances grow or decay, it also has a significant effect on the frequency of oscillation. The present work examines this interaction, and is concerned with using CFD to model the unsteady response of a confined, premixed flame. Premixed ethylene and air flowed through a choked nozzle at the entrance to the duct and the exit was open to the atmosphere.