100-Hour Test of an Inside-Out Ceramic Turbine Rotor at Operating Conditions

Converting sub-MW turbine rotor blades to ceramics is not a trivial endeavour, but the promise of a substantial increase in turbine inlet temperature (TIT), and therefore cycle efficiency and power density, could mean wide use in upcoming, distributed power, turboelectric aircraft. The inside-out ceramic turbine (ICT) rotor configuration attempts to address this by loading ceramic blades in compression, as centrifugal force pushes them against a rotating structural composite shroud. This paper reports significant experimental progress in the development of ICT rotor technology, aimed at the development of a high-efficiency, turboelectric powerpack. A 20-kW scale, single spool, recuperated ICT was operated with monolithic silicon nitride blades, for a total of 113 h above 1100 °C, including 13 h at the design tip speed of 400 m/s and a cumulative 100 h at 360 m/s, with no critical failure. ICT rotors sustained short excursions with TIT up to 1200 °C and tip speeds up to 430 m/s in hot conditions, and 500 m/s in ambient conditions. An ICT rotor was successfully integrated within a complete recuperated turbogenerator with a nested high speed electric motor. Results suggest that further work on an ICT turbogenerator should enable it to reach a TIT of 1275 °C, a target to achieve 45 % cycle efficiency in the sub-MW range.