Experimental verification of thermal insulation and cooling for 500W class micro gas turbine generator

The development of long-duration mobile energy sources suitable for mobile robots or small-sized unmanned vehicles is an area of active research. The micro gas turbine generator (MTG) is a promising solution for this purpose because it has both a high energy density and a high power density. A 500W class MTG is under development. The design of the MTG can be divided into two main parts. One part consists of the motor/generator and compressor, whereas the other part consists of the combustor, turbine, and recuperator. The 500W class MTG is designed to operate at an extremely high speed of 400,000 rpm, with a turbine temperature of over 700 °C, to improve the efficiency. Because the magnetism of the NdFeB permanent magnet for the motor/generator would degrade if it were exposed to temperatures over 150-200 °C, thermal insulation between the two parts is needed to reduce the heat transfer from the combustor and turbine. The motor/generator is also cooled by the inlet air flow driven by the compressor. This study presents the results of an experiment designed to verify whether the thermal insulation and air flow are effective enough to keep the temperature of the motor/generator part below 100 °C. From the rotating test, performed with the aid of a high-temperature test rig, it was confirmed that a temperature of less than 50 °C could be maintained in the motor/generator part, under the condition of 1.0 bar compressed air supply.