Stijn Stevens

Micropower generation with microgasturbines: A challenge

Abstract This paper describes the development of a microgasturbine with a rotor diameter of 20 mm. The target electrical power output lies around 1 kW. The total system fits in a cylinder with a diameter of 95 mm and a length of 120 mm. The system contains the same components as a large gasturbine generator: compressor, recuperator, combustion chamber, turbine, and electrical generator. Major challenges are the high rotational speed (500 000 r/min), high turbine inlet temperature (1200 K), and the efficiency of the components. Because of the small dimensions, the flow through compressor and turbine is characterized by relatively low Reynolds numbers. The higher flow losses and inherently lower efficiency require a higher blade tip speed (524 m/s) than for large turbines (300-400 m/s). To minimize wear and frictional losses, the rotor is mounted on aerodynamic bearings. To withstand the high centrifugal stresses, a high-strength steel is used for compressor and shaft. The turbine is made of a Si3N4-TiN ceramic composite to withstand the combination of elevated stress and temperature.

Integrated solution for micro power generation

Battery systems have a much lower energy density than fuels. The use of fuel based micro power generation units instead of batteries can therefore become interesting in certain applications. This paper describes the problems that occur when designing such a power generation unit. It is shown that operational conditions and geometrical restrictions impose tough requirements on the design of different components. The solutions as found in traditional fuel based generation systems cannot simply be downscaled, but several concepts have to be fundamentally rethought

A hybrid high speed electrical micromachine for micro scale power generation

This paper presents a methodology for the optimization of a new type of high speed electrical micromachine for micro scale power generation. The micromachine is integrated into the compressor of a microturbine which operates at 500,000 rpm. Because of the high energy density of fuel, the turbine-generator combination exceeds the limitations of batteries and smoothes the way for high power or long endurance applications. The micromachine is optimized for a mechanical output power of 100 W within the dimensions of the turbine. Special attention is paid to the problems caused by high speed operation and their influence on the design of the machine