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# Air RacePUBLIC ACCESS

Even with the World in Recession, Gas Turbines move ever Forward.

[+] Author Notes

Lee Langston, an ASME Fellow, is professor emeritus of the mechanical engineering department at the University of Connecticut in Storrs. He is a member and a past chair of ASME's International Gas Turbine Institute.

Mechanical Engineering 132(05), 34-38 (May 01, 2010) (5 pages) doi:10.1115/1.2010-May-3

## Abstract

This article presents an overview of the existence and use of gas turbines in the past, present, and future. The article uses the data provided by Forecast International of Newtown, Conn., which covers both aviation and nonaviation gas turbine markets. The gas turbine has proven to be an example of technological evolution, where improvements in efficiency and reliability continue to amass, 70 years after its invention. Advanced technology developed in military jet engines has often migrated to commercial jet engines and nonaviation gas turbines, and improved their performance. Gas turbine combined-cycle power plants come in all sizes. The largest combined-cycle gas turbines are the H class machines made by GE and Siemens. Given the world’s current focus on sustainable or renewable energy, how do natural gas-fired gas turbines fit in? In some instances, renewable energy, such as solar or wind, just would not be practical without assistance from gas turbines. As power production moves tentatively into a low-carbon future, or as people look for more fuel-efficient ways to cross continents, it’s a sure bet that gas turbines will be there.

## Article

New gadgets are all the rage, but most of what we think of as futuristic technology are not new at all. Nuclear power plants date from the 1950s. Electric cars are more than a century old. Even the iPad, the latest device from Apple Computer, is derived from solid state semiconductor technology from the 1960s.

The rule of thumb is that it takes several decades for a new technology to dominate a market. If it hasn’t been invented yet, it probably won’t make a difference in your life.

That makes the sudden, audacious appearance of the gas turbine in the late 1930s such a remarkable exception. In 1939, the first practical gas turbine was used to generate electricity by the Brown Boveri firm in Switzerland, and in Germany, the gas turbine developed by Hans von Ohain powered the first jet aircraft flight. That was quickly followed by a similar British flight in 1941, propelled by the gas turbine independently invented and developed by Frank Whittle, during the 1930s.

General Electric uses this model of an open rotor jet engine for wind tunnels tests of fan performance and noise.

Worldwide Gas Turbine Production

The economist W. Brian Arthur points out in his book, The Nature of Technology; What It Is and How It Evolves, published last year, that the gas turbine did not arise out of small improvements to previous energy converters such as the piston engine. It was a truly new prime mover, the first of its kind. After the Second World War there was a striking shift from piston engines to jet engines, first in military and then in commercial aircraft. The shift to gas turbine electrical generation has been slower, but now in some parts of the United States, particularly Texas and California, 50 percent of electricity is produced by gas turbine power plants.

Technology, Arthur proposes, can have interlocking meanings: As a means to fulfill a human purpose; as an assemblage of practices and components; or as the entire collection of devices and engineering practices available to a culture. And technologies evolve based on the chaotic and constant recombining of existing technologies.

The gas turbine, Arthur writes, is an example of technological evolution, where improvements in efficiency and reliability continue to amass, seventy years after its invention. Furthermore, Arthur claims that, in his view, our economy is nothing more than the clever organization of technologies to provide for our needs. Thus the economy evolves as technologies evolve.

If that's the case, then understanding how the gas turbine industry weathered the stormiest economic year in more than half a century should provide an insight to how that technology—and even the economy as a whole—will fare in the coming years.

Because of the ecumenical nature of gas turbine applications we will use the data provided by Forecast International of Newtown, Conn., which covers both aviation and non-aviation gas turbine markets. Using computer models and an extensive database to monitor value of production (considered more accurate than sales figures), FI analyst Bill Schmalzer is able to provide market data, going back to 1994 as well as FI's projections to 2014, all adjusted to 2009 U.S. dollars.

The total worldwide value of production for all gas turbines in 2009 was $40.5 billion, up 13 percent from 2008. According to FI's projections the entire gas turbine industry could grow to$51.9 billion by 2014, a 28 percent increase over 2009 and exceeding the 2001 peak of $48.3 billion, during the “irrational exuberance” of power plant expansion that followed electric utility deregulation. In other words, the power and efficiency inherent in gas turbines is so attractive, even the Great Recession can’t slow down their production. Aside from the 2001 spike, the gas turbine industry is dominated by the aviation sector. Jet engines and turboprop engines for commercial and military manned aircraft account for$27.0 billion in production for 2009, an 18 percent increase over 2008 and 67 percent of the 2009 total value of production. Commercial aviation is by far the larger portion, about five times that of military gas turbine engines.

Military engines are more glamorous, however, and Pratt & Whitney and General Electric dominate that market. They have about an equal split of engines on the F-15 and F-16 fighters, while P&W has the turbojet engines on Boeing's popular four-engine C-17 military transport.

Gas Turbine Production by Sector Production of gas turbines for commercial aviation and electric generation is set to increase over the next five years. Other sectors will remain steady.

Pratt & Whitney's geared turbofan jet engine, seen here with its nacelle opened, promises fuel savings of as much as 16 percent.

It is expected the new Joint Strike Fighter, the Lockheed Martin F-35, will account for more than 2,700 engines, according to FI's William Alibrandi. Pratt & Whitney's 40,000-pound thrust F135 engine (derived from the company's F119 engine from the Raptor F-22) is the primary JSF engine, and low-rate production is in full swing for the extensive test program under way for this remarkable aircraft. (See “Fahrenheit 3,600,” April 2007, for more on the F135.)

The GE/Rolls-Royce Fighter Engine Team is in the process of developing the F136, an alternate JSF engine, with funding that has been in the past reinstated by Congress, after being repeatedly canceled by more than one White House.

Advanced technology developed in military jet engines has often migrated to commercial jet engines and non-aviation gas turbines, and improved their performance. So the Joint Strike Fighter engine program, which is really pushing the envelope, may have an enormous impact on the future even if the F-35 never fires a shot in anger.

The $22.5 billion commercial jet engine arena—up 23 percent from 2008—was the scene of much activity. Commercial aircraft come in one of two basic flavors: Wide-body twin-aisle airliners, such as the Boeing 747 and the double-decked Airbus A380, and narrow-body single-aisle jets such as the Boeing 737 and the Airbus A320. The narrow-body market represents the biggest and the most lucrative market for engine manufacturers. For instance, Pratt & Whitney has sold over 14,000 of its venerable JT8Ds, and CFM International, owned by General Electric of the United States and Snecma of France, has sold over 18,000 units of its newer CFM56. These so-called golden engines are in the 15,000- to 32,000-pound thrust range, and are installed primarily on narrow-body aircraft. In the last few years, the price of a barrel of oil has fluctuated anywhere between$40 and an astonishing high of $145 in 2008. For the world's airlines this means that jet fuel costs account for 15 percent to 35 percent or more of their operating costs (See “Fitting a Pitch,” December 2009). It is not difficult to see that a 10 to 15 percent increase in jet engine fuel efficiency could be the difference between a pleasing profit or a baneful bankruptcy for an airline. CFM International and Pratt & Whitney are both developing engines in the 30,000-pound thrust range that promise to markedly improve fuel consumption— perhaps by as much as 16 percent. (Rolls-Royce also has an advanced three-shaft RB285 under development in this thrust range.) CFM's LEAP-X, which is an improved CFM56, will power China's new 156-seat Comac C919, slated for a first flight in 2014 and entry into service in 2016. Pratt's new geared turbofan engine, the PW1000G, will be launched on the new Mitsubishi MRJ 70- to 100-seat regional jet and the Bombardier CSeries 100- to 150-seat aircraft, both of which are planned to be in service in 2014. The recently announced Russian Irkut MC-21, a 150- to 210-seat aircraft scheduled to begin service in 2016, is also slated to use the geared turbofan engine. Those new narrow-body aircraft from China and Russia portend an encroachment in the very large market now shared by Boeing's 737 and Airbus's A320. Those two companies currently each have about 2,000 of these single-aisle aircraft on their order books, powered by the CFM56 or the International Aero Engine V2500. Both Boeing and Airbus have plans to come out with new, improved replacements for the popular 737 and A320, though not until the distant 2020s. Meanwhile their airline customers, burdened with high fuel costs and looking at the new fuel-efficient engines being offered by CFMI, P&W, and R-R, are clamoring for re-engining narrow-body aircraft being produced now, rather than waiting for all-new aircraft in the distant future. Airbus has listened to its customers and recognized the emergence of new competitors in this decade. The company is now researching the possibility of re-engined narrow-body aircraft—the A319, A321, and A320— potentially available late in 2015. That move may well cause Boeing to seriously consider re-engining its 737s. Should Boeing and Airbus begin a re-engining campaign, Pratt & Whitney's PW1000G geared turbofan may be the engine of choice. The GTF has a bypass ratio as high as 11:1—that is, 11 pounds of air bypassing the engine core for every one pound going through the engine itself. As a consequence, the engine has a large diameter fan, which could be a problem. According to Pratt officials, however, the fan will fit under the wings of an A320 or the even lower wings of a 737 without resorting to larger, and heavier, landing gear. The GTF's advantages are an improvement up to 16 percent in fuel burn and a large reduction in noise. It produces a “whoosh” sound rather than the characteristic turbofan whine. The reduction in both fuel consumption and noise is an unequaled combination. For instance, there is at least one case in the past where engine manufacturers, faced with a design choice of meeting the onerous noise restrictions of the London airports, or a reduction in fuel consumption, chose the former. The reduced fuel consumption wouldn’t sell engines, the executives reasoned, if an airplane fitted with one couldn’t land at one of the world's major airports. The five-passenger HondaJet, with twin engines mounted above the wings, is designed to be an inexpensive alternative to the standard business jet. In the quest to further reduce turbojet fuel consumption, both Rolls-Royce and General Electric are revisiting research and development of open rotor jet engines. The open rotor engine, which has also been called an unducted fan and an ultra-high-bypass engine, has the axial fan mounted outside of the engine nacelle. Current designs feature a double contra-rotating fan mounted at the aft end of the engine, driven directly or through a gearbox by the turbine. The open rotor yields a very high bypass ratio—on the order of 50:1—and may reduce fuel consumption by as much as 35 percent compared to a conventional turbofan. Two full-scale open rotor engines were tested on commercial aircraft in the late 1980s, one by Pratt & Whitney and Allison, and one by GE. Fuel prices subsequently dropped and both projects ended. Problems with the open rotor engines that an OEM faces are reducing noise, dealing with an uncontained fan blade failure (such as from a bird strike) and figuring out where to mount it on the airframe. On the lower thrust level of the market, for business jet engines, a highlight is the progress being made in 2009 with the innovative HondaJet. This five-passenger twin engine jet is made by Honda Aircraft with deliveries starting next year. At a projected price of about$3.7 million each, the aircraft is inexpensive for a business jet. The HondaJet is powered by two 2,000-pound thrust GE Honda H120 engines, each mounted in nacelles above the wing. One wonders why other airframe companies don’t go to this above-the-wing engine mount in order to reduce ground level engine noise and to accommodate larger diameter, high-bypass-ratio turbofan engines.

Growth was a bit slower on the non-aviation side. The value of production for non-aviation gas turbines in 2009 was $16.6 billion, according to Forecast International, up 6 percent from 2008. Of the 2009 non-aviation total,$11.1 billion—some 82 percent—was for gas turbines used to generate electricity. Marine power and propulsion, which make up \$416 million, and mechanical drive such as natural gas pipeline compressors make up the rest of the non-aviation segment.

In the last twenty years, simple-cycle and combined-cycle gas turbine power plants fueled by natural gas have made a huge impact on the world's electrical generation market. With fast starting, simple-cycle plants at 40 to 45 percent thermal efficiencies and combined-cycle plants approaching 60 percent, governments, utilities, and investors have funded their construction in country after country. On a per-kilowatt basis, they are far cheaper to construct than a nuclear or hydrocarbon fueled steam plant.

Rolls-Royce is developing an open rotor jet engine that could provide bypass ratios as high as 50:1.

When the wind doesn’t blow, these four Pratt & Whitney FT8 gas turbines will be used to back up 200 MW of wind turbine farms in Montana.

Gas turbine combined-cycle power plants come in all sizes. The largest combined-cycle gas turbines are the H class machines made by GE and Siemens. A new Siemens H class gas turbine, the SGT5-8000H, is rated at 340 MW, making it the world's largest gas turbine. That turbine underwent testing in 2009 at Irsching, Germany, and is the heart of a new 530 MW combined-cycle plant. At the other extreme, here at the University of Connecticut we operate a 25 MW combined-cycle cogeneration power plant, using three Solar Taurus 70 gas turbines. (I wrote about this project in December 2006).

Given the world's current focus on sustainable or renewable energy, how do natural gas-fired gas turbines fit in? In some instances, renewable energy such as solar or wind, just wouldn’t be practical without assistance from gas turbines. For instance, in Montana, NorthWestern Energy is currently constructing a 200 MW natural gas-fired Mill Creek Generating Station that will use Pratt & Whitney FT8 gas turbines to provide fast start (and stop) “regulation service” to compensate for wind power's unpredictability. In the company's own words, “Because wind is difficult to accurately schedule…it is more problematic to integrate into the transmission grid. For example, at the Judith Gap Wind Farm, the wind farm has ramped up from zero to 131 MW in 10 minutes and has ramped down from 121 MW to zero MW in a similar time period.”

As power production moves tentatively into a low-carbon future, or as people look for more fuel-efficient ways to cross continents, it's a sure bet that gas turbines will be there. If our economy is nothing more than the clever organization of technologies to provide for our needs, as W. Brian Arthur claims, then in the gas turbine we have a very good partner.

At 340 MW, the Siemens SGT5-8000H is the world's largest gas turbine.

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