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Cooreflex - Thermoacoustic characterization of autoignition stabilized, liquid fuel reheat flames

© TUB Eric Bach
© TUB Eric Bach

Gas turbine engines with sequential combustion systems are characterized by high efficiency, specific work output, and load flexibility. Beyond that, pollutant emissions compliant with legislation, the prevention of thermoacoustic combustion instabilities, and fuel flexibility are crucial for an engine’s competitiveness in today’s power generation market.

An exact understanding of the interaction between flame and combustor acoustics is imperative for the design of robust combustion systems.
For this purpose, a sequential combustion test rig was designed and commissioned at the Chair of Fluid Dynamics, combining a swirl-stabilized gas flame with an autoignition stabilized liquid fuel reheat flame. The investigation focusses on the second-stage diesel flame, which can be operated in the lean regime.

Of particular interest is the development of an interaction mechanism between the instantaneous heat release fluctuations with azimuthal acoustic modes, appearing well above 2 kHz. Currently, no coherent understanding exists of this phenomenon, also known as ‘screeching combustion’. The flame is no longer acoustically compact when subjected to these higher order modes, and, hence, has to be characterized locally. Previous investigations suggest a coupling of the heat release rate to the acoustic displacement field, and periodic compression and expansion of the reaction zone.

Within this project, a test rig with a combined thermal power of 300 kW was de-signed. An experimental investigation is carried out with multiple azimuthal micro-phone arrays as well as an array of four compression drivers. The flame response to acoustic forcing is observed via a high-speed camera in order to identify local interac-tion between heat release, flow, and acoustics. The aim of the project is the derivation of a coupling mechanism based on experimental data, enabling the prediction of flame behavior and supporting the combustor design process.



Eric Bach

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