Modeling and control of combustion oscillations

Clean combustion, with low levels of pollutants, can be achieved by burning lean and premixed. Unfortunately, these are just the conditions that cause self-excited oscillations which can become so intense that they break the combustor. Many gas-fuelled power stations have suffered damage in this way and been unable to achieve their designed power and low-emission levels. Self-excited oscillations are also being experienced in the development of the next generation of aeroengines as they strive to achieve lower emissions. These instabilities occur due to the interaction between sound and flames: the unsteady combustion generates acoustic waves and these in turn alter the inlet flow rates of fuel and air and lead to further unsteady combustion. An overview of the recent research in this area at the University of Cambridge is presented. Emphasis is placed on the physics of the interaction between sound and flames investigated through experiment and computer modeling. The elements needed for effective prediction and modeling are discussed, together with the potential of 'anti-sound' and passive acoustic absorbers to eliminate the instability.