Control of combustion driven acoustic oscillations using plasma discharges

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Combustion instabilities are a major issue for the design of modern combustion chambers in aero-engines and stationary gas turbines for power generation. One promising approach to suppress the high-amplitude pressure pulsations associated with these thermoacoustic instabilities is based on active control of the system dynamics. Several studies over the past 20 years have demonstrated the capability of this approach, using mostly acoustic forcing and fuel injection modulation as actuation mechanisms. However, the applicability of these methods in full-scale engines remains limited, due to restrictions in available actuator technology and performance.In 2012, the two partners involved in the proposed project, EM2C (France) and TUB (Germany), successfully tested the use of non-equilibrium plasma discharges to control combustion dynamics. The proof of concept has been realized that nanosecond repetitively pulsed (NRP) discharges can be used as an actuation mechanism for active control of combustion instabilities, without the drawbacks of traditional actuators such as loudspeakers or fuel valves. However, while this preliminary study was promising, the unsteady coupling between plasma and flame dynamics remains unclear and must be further investigated to uncover the full potential of this novel approach.The proposed project therefore aims at (1) acquiring a fundamental understanding of the coupling of combustion dynamics and non-equilibrium plasma discharges, (2) the experimental evaluation of the potential of non-equilibrium plasma discharges for active control of combustion instabilities. Experimental work will be performed in France and in Germany, in order to benefit from the complementary expertise of the two partners. Fundamental studies of plasma-acoustic and plasma-flame interaction will be carried out, in dedicated generic set-ups. With the help of numerical simulations of plasma-flame interaction, an empirical model of the effect of NRP plasma discharges on the combustion dynamics of lean premixed flames will be derived. The influence of NRP discharges on the dynamics of swirl-stabilized lean premixed flames will be investigated, including acoustic, chemical and hydrodynamic effects. A plasma actuator will be implemented in an atmospheric combustor test-rig with a fully turbulent swirl-stabilized flame. The response of the flame to plasma forcing will be measured with acoustic and optical methods, and the obtained actuator transfer function will be used in conjunction with a thermoacoustic system model to develop appropriate control schemes. Feedback control will then be applied to mitigate combustion instabilities in the test-rig.