Effect of the Radial Swirler Ellipticity on Hydrogen Flames in a Micro-Gas Turbine Combustor

A radial swirler burner with an elliptic cross section has been developed for a micro-gas turbine combustor that is commissioned to accommodate hydrogen combustion in the premixed flame mode. A numerical model has been established to explore the swirling combustion performance using the partially premixed flamelet-generated manifold combustion model via employing detailed chemical kinetics. The swirler cross-section aspect ratio has been varied in the range from 1 to 2 at a vane angle of 40 degrees, while the combustion performance was investigated for both fuel conditions of pure hydrogen and 50%/50% hydrogen-methane blend at full load and 50% load. While the results demonstrated the key flow field features, the flame shape as well as the exhaust NOx and CO emissions, it was found that increasing the aspect ratio significantly increased the turbulent kinetic energy and the resultant flow strain. Increasing the aspect ratio additionally increased the peak reverse flow velocity. Inasmuch as this was associated with higher rates of excess air entrainment, the peak flame temperature and the corresponding NOx emissions were reduced on the account of increasing the total pressure drop particularly at the maximum aspect ratio. In this regard, the NOx and CO emissions, respectively, decreased by up to 33% and 46.6% at the aspect ratio of 2.0. As driven by the highly strained reactive swirling flow, the hydrogen-methane premixed flame acquired extension in the flame stability limits. This was accompanied by a consequent reduction in the flow residence time and species re-distribution for NOx formation. The elliptic cross-section radial swirler has thus been proven to be an innovative flow configuration which effectively improves the combustion performance and reduces the resultant emissions.