Aircraft Gas Turbines

An estimated 75% of the components of modem aerospace gas turbines are coated, in both the hot and cold sections. This includes stator shrouds and vanes, blade platform edges, blade z-notches, blade tips and shroud tops, and combustor-liner interior surfaces. The use of ceramic coatings in aerospace turbines is being expanded to marine and industrial gas turbines which have similar (and often more acute) environmental problems. 

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Demands for improved efficiency in aircraft gas turbines led to the use of a family of age hardenable, controlled expansion superaHoys for engine seals and casings. INCOLOY aHoys 903 [61107-16-2] (UNS N19903), 907 [107652-23-3] (UNS N19907), and 909 evolved from a continuing effort to improve the environmental resistance of this Cr-free, Fe—Ni—Co based system. 

Hard facing of various components in the aircraft gas-turbine engine and in industrial apphcations for textile machinery parts, oil and gas machinery parts, paper-shtting knives, etc, is estimated at 1 x 10 in 1995 with an estimated growth rate of 5% annually. The mix is approximately 45% aerospace apphcations, 55% industrial apphcations. Additionally, repair coatings for gas-turbine blades and vanes is estimated at 500 x 10 . These coatings are primarily deposited by plasma spray, arc-wire, HVOF, and detonation gun techniques. 

Operation of aircraft gas turbines on a wider cut than the 160—260°C fraction of cmde to expand avadabihty has been considered (24). Boiling range is limited at the low boiling end by flammabdity, ie, flash point, and at the high boiling end by low temperature needs, ie, freezing point. In the case of Jet A, a reduction of flash point from 38°C to 32°C would increase yield by 17% an increase in Jet A1 freezing point to —40°C would add about 25% to the kerosene pool. 

Synthetic fuels derived from shale or coal will have to supplement domestic suppHes from petroleum someday, and aircraft gas turbine fuels producible from these sources have been assessed. Shale-derived fuels can meet current specifications if steps are taken to reduce the nitrogen levels. However, extracting kerogen from shale rock and denitrogenating the jet fuel are energy-intensive steps compared with petroleum refining it has been estimated that shale jet fuel could be produced at about 70% thermal efficiency compared with 95% efficiency for petroleum (25). Such a difference represents much higher cost for a shale product. 

In the last chapter we saw how a basic knowledge of the mechanisms of creep was an important aid to the development of materials with good creep properties. An impressive example is in the development of materials for the high-pressure stage of a modern aircraft gas turbine. Here we examine the properties such materials must have, the way in which the present generation of materials has evolved, and the likely direction of their future development. 

Current and Future Materials Usage in Aircraft Gas Turbine Engines, Metals and Ceramics Information Center, Battelle Laboratories, 505 King Avenue, Columbus, Ohio 43201, USA. 

The aircraft gas turbine engine, developed more than sixty years ago, uses the principle of jet reaction and the turbine engine. The engine consists of three major elements a compressor and a turbine expander, which are connected by a common shaft and a combustor, located between the compressor and the turbine expander. The useful work of the engine is the difference between that produced by the turbine and that required by the compressor. For the simple cycle system shown in Figure 1, about two-thirds of all the power produced by the turbine is used to drive the compressor. 

Zipkin, M. A. (1977). Evolution of the Aircraft Gas Turbine Engine. Israel Journal of Technology 15 44—48. 

Parts or process plant machines marine main-turhine gears centrifuge drums fans assembled aircraft gas-turbine rotors fly wheels pump impellers machine-tool and general machinery parts electrical armatures. 

Aluminium diffusion calorising, aluminisingY protects steels against oxidation at elevated temperatures, and the more recently developed processes for aluminising and chromaluminising superalloys are widely used to increase the life and operating temperature of aircraft gas turbine vanes, etc. 

Co 0.011 0 0.0524 7 134 34,833 383 1,825 43% superalloys, which are used mainly in aircraft gas turbine engines 9% was in cemented carbides for cutting and wear-resistant applications 22% was in various other metallic uses. 

McCAFFERTY AND HIBBARD—COMBUSTION IN AIRCRAFT GAS TURBINE ENGINES... 

The modulated swirl combustor decribed here (2) represents a step in this direction when operated with propane or hquid kerosene. It exhibits a very distinct change in flow pattern and potentially can satisfy pollution legislation over a wide operating range of heat release rates, as required, for example, in an aircraft gas turbine engine combustor. 

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