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Thermoacoustics



Investigating combustion oscillations with phase-resolved diagnostics

 Monitoring the interaction between flow field and flame in a swirl burner having typical design features of a gas turbine combustor. The image shows a part of the combustion chamber with the burner outlet at the bottom edge. An acoustic oscillation of approx. 300 Hz was identified in the burner. The position of the flame - made visible here by laser-induced fluorescence of the CH radical – shows a corresponding periodic movement correlating with the fluctuation of the flow field.
zum Bild Monitoring the interaction between flow field and flame in a swirl burner having typical design features of a gas turbine combustor. The image shows a part of the combustion chamber with the burner outlet at the bottom edge. An acoustic oscillation of approx. 300 Hz was identified in the burner. The position of the flame - made visible here by laser-induced fluorescence of the CH radical – shows a corresponding periodic movement correlating with the fluctuation of the flow field.

In advanced stationary gas turbines, the concept of lean premix combustion is applied to reduce NOx emissions. Using a homogeneous, lean mixture prevents temperature peaks in the combustion chamber, thereby significantly reducing thermal NO formation. However, lean premix combustion is very susceptible to combustion instabilities, especially to thermoacoustic pulsations. Since the underlying physical and chemical processes of instabilities are inadequately understood, “thermoacoustics” is a current research topic. We apply measurement techniques in a phase-correlated manner, i.e. the lasers and detectors are triggered with a defined phase relationship to the pressure fluctuation in the combustion chamber, in order to record the dynamic behaviour of key measurement quantities. By applying Raman, LIF and PIV measurement techniques, it has been possible to calculate the phase-dependent variations of mass flows in the combustion chamber and to show how they are related to the heat release. The sets of measurement data thus obtained show quantitatively, for the first time, how the combustion pulsations are sustained by the interaction between heat release, flow and acoustics.

Thermoacoustic oscillations have been studied by us in various swirling flames, for example, from laboratory scale to technically relevant high-pressure burners, e.g. the DLR double-swirl burner (gas film nozzle), the TM premix burner of the EU PRECCINSTA project, the double-swirl burner of the Collaborative Research Center 606 or scaled industrial gas turbine burners.


Research Fields
Development of methods
Sooting flames
Thermoacoustics
Alternative fuels
Standard flames
Gas turbine combustion
Applications
Equipment
Related Topics
Acoustics
Lasers and Masers
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