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Unformatted text preview: Alan H. Epstein Gas Turbine Laboratory Massachusetts Institute of Technology Cambridge, MA 01239 e-mail: Epstein@mit.edu Millimeter-Scale, Micro-Electro- Mechanical Systems Gas Turbine Engines The confluence of market demand for greatly improved compact power sources for por- table 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 100s 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 centrifu- gal 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, manufactur- ing, materials, component design, accessories, applications, and economics. It discusses the underlying technical issues, reviews current design approaches, and discusses future development and applications. @ DOI: 10.1115/1.1739245 # Introduction For most of the 60-year-plus history of the gas turbine, eco- nomic forces have directed the industry toward ever larger en- gines, currently exceeding 100,000 lbs of thrust for aircraft pro- pulsion and 400 MW for electric power production applications. In the 1990s, interest in smaller-size engines increased, in the few hundred pound thrust range for small aircraft and missiles and in the 20250 kW size for distributed power production ~ popularly known as microturbines ! . More recently, interest has developed in even smaller size machines, 110 kW, several of which are marketed commercially, @ 1,2 # . Gas turbines below a few hundred kilowatts in size generally use centrifugal turbomachinery ~ often derivative of automotive turbocharger technology in the smaller sizes ! , but are otherwise very similar to their larger brethren in that they are fabricated in much the same way ~ cast, forged, ma- chined, and assembled ! from the same materials ~ steel, titanium, nickel superalloys ! . Recently, manufacturing technologies devel- oped by the semiconductor industry have opened a new and very different design space for gas turbine enginesone that enables...
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- Spring '08