Characterization of a Fluidically-Variable Swirl Burner: Effects of the Imprinted Swirl on Flame Shapes and Emissions for Hydrogen-Methane Blends

Abstract Gas turbine combustors rely on swirling flows for flame stabilization. The flow’s swirl number is herein usually characterized by the swirler geometry within the burner. In addition to flame stability, the induced swirl represents an important parameter affecting emissions, flame shapes, and flame dynamics. The swirl dependency is furthermore gaining importance with the progression of hydrogen-enriched fuels. Hydrogen flames are found to be well stabilized by axial jets, whereas a stable methane combustion is optimally maintained by highly swirled flows. The active variation of swirl is therefore found to play a significant role, and thus represents a cornerstone of the present study. In this work, the experimental characterization of a novel swirl-stabilized burner is presented. It allows for the variation of the swirl number imparted through fluidic actuation, not employing geometry variations, and capable of creating a linearly controllable flow regime ranging from a non-swirled to a fully swirled flow. This concept is characterized under reacting conditions. For a broad range of hydrogen-methane gas mixtures, the characteristics of the burner and the stabilized flames are experimentally investigated. For each fuel blend, a wide span of operating points is created with different swirl regimes. The emissions within the exhaust gas are analyzed through a gas analyzing system and the respective flame shapes are acquired through OH*-imaging. The characterization of the novel burner concept demonstrates its operational capability over a broad operational range. For each fuel composition, an optimal degree of swirl could be identified, allowing for a stable combustion, and minimizing the emissions. Additionally, all stable operating points are mapped, quantifying the operational limits of the investigated burner.