Active Control of Combustion and its Applicatons

Abstract : The ducted flame in any of its forms can have the tendency to interact with its surroundings. When this interaction takes the form of thermo-acoustic instabilities the consequences can be grave. These instabilities have been recognised as a problem for many decades and have appeared in many forms of engine including rocket motors, ramjets, main engine gas turbine combustors and after burning system. It is true to say that the phenomena has not been truly understood and that many researchers have come up with several theories as to how these thermo-acoustic instabilities occur. In the field of engineering, the ability to fix the problem rather than fully understand the problem has been a principle that has been applied for many years. The approaches taken to fixing thermo-acoustic, problems have been either radical re-design of the combustion system or the application of passive damping techniques. In the past decade, however, a further technique has been given to the combustion designer, that technique being the ability to use active control. This paper outlines how the technique has been developed, from small scale pilot rig testing through to full engine demonstration, and how active control may be applied to land-based gas turbines in the future. With the introduction of ultra low emission lean pre-mixed combustion systems to land based gas turbines the propensity to exhibit thermo-acoustic instabilities has increased. Actively controlling the instability is a real option, the benefits of gaining extensive experience with the technology on land will help to promote the technology for future application to aircraft.