A study on innovative gas turbine core concepts supported by the NEWAC project (NEW Aero-engine Core concepts, Integrated Project co-funded by the European Commission within the Sixth Framework Programme under contract No. AIP5-CT-2006-030876) focused on the ability of the combustor to maintain combustion during a drastic reduction of the main air, e.g. due to an active control on the core flow to improve the off-design efficiency. A feasibility study was performed at Graz University of Technology including dimensioning, design and validation of a test burner with variable geometry. A low power premixed methane / air burner with swirl-stabilised flame was chosen, on which the outlet surface and the ratio axial to tangential momentum on the mass flow rate could be controlled. During testing at atmospheric conditions, special attention was paid to the extension of the flammability domain and to the flame dynamics (transition attached-detached, flame stability, blowout limits). It was established for instance that based on this technology, a detached flame can be maintained when reducing the design mass flow rate by 40 per cent within a safe stability range. The paper discusses the background of the study, the burner’s design and technology, the measurement techniques and the results of the validation campaign. A discussion on possible advantages of using variable geometry in a combustion chamber versus conventional technologies closes the paper, taking into account the technical challenges to be met.

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