Major Areas of Opportunity - Implications of Emerging Micro-and Nanotechnologies - page 98

A somewhat different application of MEMS technology offers new ap-
proaches to old gas turbine problems, namely the dynamic system instabilities
that plague gas turbines, including rotating stall and surge, combustor instabili-
ties, airfoil flutter, and inlet instabilities. The control or suppression of these
instabilities offers improved range payload (by 10-15 percent for surge and stall),
reduced emissions, and reduced maintenance. Although the underlying physics
and implementation details may vary, the control implementations for these in-
stabilities share the common elements of distributed sensing and actuation. While
there are no specific requirements for a MEMS-scale device, the actuation fre-
quencies needed are difficult to achieve with other technologies. Also, technol-
ogy solutions using large numbers of sensors and actuators are usually quite
sensitive to unit cost, which could be low with micro- and nano-approaches.
Micro- and nanotechnologies may also have much to contribute in the area of
engine controls and accessories. The control system of a modern aircraft engine
now accounts for over 15 percent of the acquisition cost and 40 percent of the
maintenance and overhaul costs. One major engineering challenge for these sys-
tems is the high temperature, which currently requires that many of the sensors
and electronics be located remotely in a cooled environment, thus increasing
complexity and cost and discouraging redundancy. High-temperature micro-
sensors and accompanying electronics would be very attractive from a systems
viewpoint and might be an enabling technology for some of the flow control
schemes discussed above. SiC- and GaN-based, high-temperature micro-elec-
tronics and MEMS is the most common research direction aimed at solving this
problem. Another approach might use lower temperature electronics locally pack-
aged with chip-level MEMS-based coolers.
Gas turbine fuel controls consist of two principal elements: a computer and a
fuel-metering unit controlled by the computer, which consists of redundant trans-
ducers, valves, and actuators. These units are now custom engineered for each
application, so that many different models are manufactured in small quantities
and at great cost. MEMS offers the possibility of developing a standard (albeit
very small capacity) integrated fuel management unit, numbers of which operat-
ing in parallel would provide the fuel flow required for different size engines.
This approach could offer the benefits of lower cost and higher reliability (since
the multiple units operate in parallel). Fuel pumps might also be amenable to a
similar approach (at least for small engines).
Technical issues for these evolutionary improvements to air-breathing turbo-
machinery include the integration of MEMS sensors and actuators onto curved
surfaces, the transmission of data across rotating surfaces, the development of
instability control algorithms and active control for specific applications, and the
ability of MEMS sensors and actuators to survive high-temperature chemically
reacting flows without fouling. Testing and diagnostic efforts using relevant
turbomachinery need to be initiated.