Recent projections foster the belief that small high temperature heat exchanged gas turbines incorporating ceramic rotors, and ceramic exhaust beat exchangers, may eventually have thermodynamic efficiencies competitive with Diesel cycle engines. Small high speed Brayton cycle gas turbine turbogenerators on the near term verge of production will indeed have improved thermal efficiencies, but ceramic material technology has not yet matured to the engine production stage. Although thermal efficiency is a dominant driver, manufacturing costs and long term engine durability are still a major concern to the engine manufacturer. As a consequence the thermodynamic performances of small gas turbines are still, in this last decade of the 20th century, primarily constrained by the temperature limits of the metallic stator/rotor and metallic heat exchanger.
This paper reviews optimum thermo-economic design considerations for a small 50 KW output turbogenerator, covering the effect of cycle performance parameters on, engine configuration, rotational speeds engine weight, manufacturing and direct operating costs. The effect of design pressure ratio on part load thermal efficiency is also addressed for applications with extended operating time at low output powers.