Identification, Modeling and Control of Nonlinear Thermoacoustic Instability

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Spontaneous pressure and heat release rate oscillations can get excited in combustion systems (employed commonly in land-based gas turbines, aero-engines and furnaces) due to coupling between the acoustic modes of the system and unsteady heat release rate from the source of combustion. These self-excited oscillations result in high noise levels, increased emission of NOx gases and reduced life span of the combustion system. In extreme cases, the emergence of such oscillations can lead to complete system failure. Hence, there is a huge impetus for investigations on thermoacoustic instability in practical combustion systems. Recent research on combustion systems has revealed that inherent dynamics of self-excited thermoacoustic oscillations, previously believed to be restricted to limit cycle behavior, can undergo bifurcations leading to highly complex nonlinear behavior, including chaotic dynamics. This fundamental discovery creates the need to redefine conventional analyses and control strategies applied in thermoacoustic systems. The focus of the proposed project is on investigating nonlinear dynamics of thermoacoustic oscillations and formulating active control strategies that take nonlinearities of self-excited oscillations into account. Three main objectives have been defined for the project: a) development of techniques for the identification of nonlinear characteristics of thermoacoustic oscillations, b) development and implementation of nonlinear, model-based control strategies, designed specifically to control bifurcations and complex (periodic, quasi-periodic and chaotic) nonlinear states, and, c) investigating the describing function approach in the light of nonlinear oscillations and formulating an extension to tackle complex behavior of self-excited thermoacoustic oscillations, in addition to limit cycle behavior. The proposed research is not only a fundamental study of one of the most interesting naturally occurring nonlinear coupling, but is also of a high and immediate significance to address one of the most crucial and long-standing issues in the power and propulsion industry.