Combined heat and power (CHP) concepts for small scale distributed power generation offer significant potential for saving energy and reducing CO2 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 technology for the turbomachinery. In 2010, the development towards a 12.2% efficient demonstrator has been described in [1]. The underlying paper describes the subsequent performance 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 redesign of the turbine scroll.
A detailed CFD study was performed to predict compressor design adaption effects on performance. A 60° sector 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 pressure boundary condition, the stationary flow field has been calculated for several operating points. The calculations have been carried out for both the original design and the adapted design.
Results showed that pressure ratio could be increased from 2.9 up to 3.2 using simple adaptations (from the turbocharger original design) while maintaining isentropic efficiency.
Finally, results of the test program and test analysis work are presented.
