A Fundamental Framework for the Robust Stabilization of Gas Turbine Combustion Instability

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This project addresses the challenge of actively controlling unstable pressure oscillations occurring in combustion systems. While the research focuses on gas turbines applications it can have impact on other combustion devices like industrial process furnaces and boilers. For all of these systems, there is a strong societal push to improve combustion efficiency, reduce harmful emissions such as nitrogen oxides, and accommodate variations in consumer power demand. The work of this project will drive improvements in combustion system stability, reliability, durability, and emissions. These improvements will be especially valuable for the stationary gas turbines providing reserve generation capacity to the power grid. Achieving these goals of high efficiency and low emissions often involves operating closer to combustion instability. Unstable combustion can be disruptive and physically damaging, and is triggered when the dynamics of heat release, fluid mechanics, and acoustic wave propagation are mutually reinforcing. There is a rich existing literature that provides insights into the physics behind combustion instability, and also shows that active control can mitigate this instability. However, many of the control strategies over-simplify the modeled dynamics and do not take advantage of advanced control strategies and consequently prevent active combustion stability control from having a practical/industrial impact commensurate with previous laboratory research successes. This project will lead to novel formulations for mathematically describing the combustion phenomena and innovative ways to control instabilities occurring during the combustion process with experimental validation. The research plan includes the participation of both undergraduate and graduate students through a unique multi-disciplinary training opportunity. An undergraduate-level laboratory experiment will be developed from this work, providing a large number of undergraduate engineering students with the opportunity to apply nonlinear control theory to critical power technologies.This work will furnish a novel fundamental framework for robust, multivariable, combined passive/active combustion stabilization during both steady-state and transient operation, and validate it using a flexible laboratory combustion rig. The framework will utilize nonlinear model reduction to develop control-oriented, reduced models of combustion instability that include more accurate physics, validated using experiments. Further, it will analyze the degree to which combustion modeling and parameterization uncertainties can penalize the performance, stability, and robustness of model-based combustion control. The framework utilizes robust, multivariable control theory to design combustion control algorithms capable of exploiting multiple sensors and actuators. Nonlinear model predictive control will stabilize combustion dynamics not just around a particular operating condition, but also during transient switching between operating conditions. Finally, the research will exploit combined design/control optimization to develop passive combustor designs inherently conducive to active stabilization. The broader impacts of this work will reach the technical community, industry, and students at both the graduate and undergraduate level. The technical progress made in this work will demonstrate the use of robust, multivariable control theory for both instability control and design of better combustor systems. The potential for improving combustor design can be translated to industrial use and gas turbine combustor design.