Millimeter-Scale, MEMS Gas Turbine Engines

Abstract

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 1 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 1940’s. 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.

Investigation of combustion in miniaturised combustor for application to micro gas turbines

“…Micro gas turbines are expected to o¨er the highest power density and, therefore, several research groups have initiated programs to develop ultra micro gas turbines, following the pioneering work of the MIT group [1]. At ONERA, a research program is ongoing [2], with the support of the Ministry of Defence (DGA/UM AERO), aimed at developing a demonstrator of a micro gas turbine engine delivering electrical power between 10 and 100 W. The main application of this tiny engine is microdrone propulsion (15 cm length and wingspan).…”

Ultra Micro Gas Turbines

“…As a first approximation, we assumed that the manufacturing process and clearances fit with the parameters imposed for the Balje charts. This assumption is not far from reality, because the design of such small devices is strongly constrained by factors unrelated with fluid-dynamics, so that ultra-micromachines are indeed all quite similar to each other, and because the estimated clearances [Epstein 2003] are in the same range as those reported on the Balje charts.…”

“…The power density scale with the square of the force of the electric field, with the frequency and the rotational speed. Numerous possible configurations for an electrical motor-generator exist; the first choice made by the MIT researchers is an induction machine, because this type of machine does not require a direct contact between the electrical device and the rotor neither the exact knowledge of the position of the rotor [Epstein 2003]. The rotor is composed by a layer of 5-20 µm of good insulator covered by a thin layer of a low conductor (high superficial resistance), while the stator is composed by a series of radial electrodes conductors supported by an insulating layer.…”

“…(note: the residence times are calculated using inlet pressure and an average flow temperature of 1000 K) Table 2. Comparison between a conventional combustor and a micro combustor [MIT prototype -Epstein 2003] to maintain the Damkohler number higher than the unit. It can act in two ways: increase the fluid dynamic time to complete the combustion or decrease the necessary residence times.…”

“…Their realization is realized by micro manufacturing of planned rings that have been inserted in the case (for the statoric part), and the other ring is located on the faces the rotor impeller (usually the compressor, to avoid the high temperatures problems); • the rotational speed is within 150 000 ÷ 350 000 rad/s (in some cases > 500.000) [Epstein 1999[Epstein & 2003 In figure 3 it shown a prototype realized from the M.I.T., that can be consider as the "symbol/emblem" of these researches carried out during the last few years in microturbines. It is constituted by a overlapping layers in sequence, starting from the compressor, the toroidal combustion chambers and the turbine.…”