A model to study spontaneous oscillations in a lean premixed combustor using non linear analysis

To the design and operation of Gas Turbine engines a key element is the reduction of polluting emission of CO and NOx. To this end the use of lean premixed combustion systems is employed already for stationary engines, and now to be extended to aero GT engines. This kind of combustion design is vulnerable to high amplitude pressure pulsations that may develop because of the coupling between the pressure field and the heat release fluctuations, known as thermoacoustic instabilities, that can result in structural damage. For aero engines the need to predict and avoid these instabilities is even more important than for stationary engines. In order to set up a prediction model based on the transition point from stable to unstable a nonlinear dynamics analysis is proposed. Nonlinear analysis, as opposed to a linear one gives an insight of the limit cycle behavior through unstable and transient regimes by the generated attractors. A comparison between the results obtained at different points in an atmospheric pressure combustion setup, with a partially premixed turbulent methane/air flame are presented