Performance Optimization of a 3kW Microturbine for CHP Applications

Combined heat and power (CHP) concepts for small scale distributed power generation offer significant pote ntial for saving energy and reducing CO 2 emissions. Microturbines are an interesting candidate for small CHP systems with advantages in terms of performance, size, noise and costs. MTT has developed a 3kW recuperated microturbine for micro CHP applications, using turbocharger technolo gy for the turbomachinery. In 2010, the development towards a 12.2% efficient demonstrator has been described in [1]. T he underlying paper describes the subsequent performan ce optimization work done to obtain the 18% turbogenerator electric efficiency target. The work included research focused on improving several components and auxiliary systems resulting in many small loss reduction steps. Combustor performance was improved and emissions reduced. Large steps were made by improving compressor and turbine performance. Compressor efficiency and pressure ratio were optimized to obtain maximum cycle efficiency. Turbine efficiency was improved by a re design of the turbine scroll. A detailed CFD study was performed to predict compressor design adaption effects on performance. A 60° secto r model was used including inlet duct, impeller (including tip clearance) and diffusor. With prescribed inlet total pressure and total temperature and by varying the outlet static pressu re boundary condition, the stationary flow field has been calcu lated for several operating points. The calculations have bee n carried out for both the original design and the adapted design . Results showed that pressure ratio could be increas ed from 2.9 up to 3.2 using simple adaptations (from the tu rbocharger original design) while maintaining isentropic effic iency. Finally, results of the test program and test analy sis work are presented. NOMENCLATURE ηe [%] Electric efficiency (of turbo generator) ηenet [%] Net electric efficiency (for turbo