Investigation of the Down-Scaling Effects on the Low Swirl Burner and its Application to Microturbines

About 75% of the electric power generated by centralized power plants feeds the energy needs from the residential and commercial sectors. These power plants waste about 67% of primary energy as heat emitting 2 billion tons of CO₂ per year in the process (∼ 38% of total US CO₂ generated per year) [1]. A study conducted by the United States Department of Energy indicated that developing small-scale combined heat and power systems to serve the commercial and residential sectors could have a significant impact on both energy savings and CO₂ emissions. However, systems of this scale historically suffer from low efficiencies for a variety of reasons. From a combustion perspective, at these small scales, few systems can achieve the balance between low emissions and high efficiencies due in part to the increasing sensitivity of the system to hydrodynamic and heat transfer effects. Addressing the hydrodynamic impact, the effects of downscaling on the flowfield evolution were studied on the low swirl burner (LSB) to understand if it could be adapted to systems at smaller scales. Utilizing particle image velocimetry (PIV), three different swirlers were studied ranging from 12 mm to 25.4 mm representing an output range of less than 1 kW to over 23 kW. Results have shown that the small-scale burners tested exhibited similar flowfield characteristics to their larger-scale counterparts in the non-reacting cases studied. Utilizing this data, as a proof of concept, a 14 mm diameter LSB with an output of 3.33 kW was developed for use in microturbine operating on a recuperated Brayton cycle. Emissions results from this burner proved the feasibility of the system at sufficiently lean mixtures. Furthermore, integration of the newly developed LSB into a can style combustor for a microturbine application was successfully completed and comfortably meet the stringent emissions targets. While the analysis of the non-reacting cases was successful, the reacting cases were less conclusive and further investigation is required to gain an understanding of the flowfield evolution which is the subject of future work.