The reduction of polluting NOx emission remains a driving factor in the design process of swirl-stabilized combustion systems to meet strict legislative restrictions. In reacting swirl flows, hydrodynamic coherent structures, such as periodic large-scale vortices in the shear layer, induce zones with increased heat release rate fluctuations in connection with temperature peaks, which lead to an increase of NOx emissions. Accordingly, flame and flow dynamics play an important role regarding the generation of NOx emissions. Beside large-scale vortices induced by symmetric thermoacoustic modes, helical coherent structures induced by the precessing vortex core (PVC) influence the flow and flame dynamics of reacting swirl flows under certain operating conditions.

We developed an active flow control system, which allows for a targeted actuation of the PVC to investigate its impact on important combustion properties. In this study, the direct active flow control is used to actuate a PVC of arbitrary frequency and amplitude, which facilitates a systematic study of the impact of the PVC on NOx emissions. In the course of the present work, partially and perfectly premixed swirl-stabilized flames are studies in connection with time-resolved OH\* chemiluminescence and PIV measurements regarding their flow and flame dynamics. The impact of these dynamics is related to the measured NOx emissions, which grow with increasing PVC amplitude in case of thermoacoustically stable flames. For flames featuring self-excited thermoacoustic oscillations, the PVC interacts with the symmetric thermoacoustic modes. This interaction changes the flame dynamics and with that the NOx emission depending on the PVC amplitude. Although, the self-excited thermoacoustic oscillations are the main driver for an increased vorticity along the flame front, the PVC tends to slightly change the dynamics in different ways such that either an increase or a decrease of NOx emissions can be observed.


Impact of the Precessing Vortex Core on NOX Emissions in Premixed Swirl-Stabilized Flames: An Experimental Study

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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