Millimeter-Scale, Micro-Electro-Mechanical Systems Gas Turbine Engines

The confluence of market demand for greatly improved compact power sources for portable electronics with the rapidly expanding capability of micromachining technology has made feasible the development of gas turbines in the millimeter-size range. With airfoil spans measured in 100’s of microns rather than meters, these “microengines” have about 1 millionth the air flow of large gas turbines and thus should produce about one millionth the power, 10–100 W. Based on semiconductor industry-derived processing of materials such as silicon and silicon carbide to submicron accuracy, such devices are known as micro-electro-mechanical systems (MEMS). Current millimeter-scale designs use centrifugal turbomachinery with pressure ratios in the range of 2:1 to 4:1 and turbine inlet temperatures of 1200–1600 K. The projected performance of these engines are on a par with gas turbines of the 1940s. The thermodynamics of MEMS gas turbines are the same as those for large engines but the mechanics differ due to scaling considerations and manufacturing constraints. The principal challenge is to arrive at a design which meets the thermodynamic and component functional requirements while staying within the realm of realizable micromachining technology. This paper reviews the state of the art of millimeter-size gas turbine engines, including system design and integration, manufacturing, materials, component design, accessories, applications, and economics. It discusses the underlying technical issues, reviews current design approaches, and discusses future development and applications.