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Gas Turbines are Changing the World–in the Air and on Land.

[+] Author Notes

Lee S. Langston is an ASME Fellow and professor emeritus of the mechanical engineering department at the University of Connecticut in Storrs.

Mechanical Engineering 137(06), 32-37 (Jun 01, 2015) (6 pages) Paper No: ME-15-JUN-1; doi: 10.1115/1.2015-Jun-1

Abstract

This study analyses the changes that gas turbines have brought in the field of air and land transport and technology. The worldwide production of gas turbines includes the commercial and military aviation markets, as well as non-aviation markets for electrical generation, marine applications, and mechanical power. In recent years, gas turbine combined-cycle plants have become key players in the generation of electric power. Aviation gas turbines make up the largest segment, whereas, the non-aviation gas turbine market is characterized by a particular vitality and volatility. The original equipment manufacturers (OEM) who supply large gas turbine combined-cycle plants are General Electric (GE), Siemens, Mitsubishi, and Alstom. And soon, the industry will be consolidated further, as GE is in the process of acquiring the power segment of Alstom, thus narrowing the field of large plant OEMs to a big three – similar to the threesome in aviation: GE, Rolls-Royce, and Pratt & Whitney – with GE in the lead.

Article

Too often we take for granted the safety and convenience that modern technology provides. We don’t consider a troubled pregnancy successfully completed to be a miracle or an infected wound to be a life-threatening predicament, such is the routine excellence of medical care. Cell phones have taken a lot of the guesswork out of life—and have made the plots of many old movies obsolete.

And lest anyone doubt the efficiency and reliability of the modern commercial jet engine, we should remember that transoceanic flights which now seem almost routine were once supported with a small fleet of ships stationed in the north Atlantic and Pacific oceans.

Retired airline pilot Captain Paul Eschenfelder recently reminded me of the past existence of these so-called weather ships. Eschenfelder recalled talking with Ocean Station November in the mid-1970s as the jet-powered airliner he piloted passed over the ship. (After official reporting was completed, he would read them baseball scores, a welcome message in their isolated location.)

They were positioned not only for weather reporting, but also to aid in possible search-and-rescue operations for piston-engine-powered airliners in trouble.

For instance on Oct. 16, 1956, Pan American Flight 6, a Boeing 377 Stratocruiser was on an around-the-world leg between Honolulu and San Francisco. After passing the point of equal flight time, two of the four piston engines failed and the crew was forced to ditch in the Pacific Ocean. The potential calamity was averted thanks to the U.S. Coast Guard cutter Pontchartrain, which was on monitoring duty at the Ocean Station November, 30̊ North and 140̊ West. All 31 crew and passengers on the plane were rescued by the Pontchartrain, but 44 cases of live canaries in the 377's cargo hold were lost when the plane sank.

That Pan Am Clipper was powered by four Pratt & Whitney piston engines. Although emblematic of the pioneering age of air travel, those commercial aviation piston engines were prone to failure. One gauge of that lack of reliability is that an aviation piston engine manufacturer could expect to sell 20 to 30 times the original cost of an engine in aftermarket parts.

A Boeing 377 on a 1956 round-the-world flight ditched in the Pacific when two of its four engines failed. Fortunately, a U.S. Coast Guard weather ship was stationed nearby and rescued the passengers before the plane sank.

Image credit: Boeing Company (top), William Simpson, U.S. Coast Guard (insets).

Grahic Jump LocationA Boeing 377 on a 1956 round-the-world flight ditched in the Pacific when two of its four engines failed. Fortunately, a U.S. Coast Guard weather ship was stationed nearby and rescued the passengers before the plane sank.Image credit: Boeing Company (top), William Simpson, U.S. Coast Guard (insets).

By contrast, commercial jet engines require only about two to three times their initial costs in aftermarket parts. Similarly, the current inflight shutdown rate of a commercial jet engine is less than 1 per 100,000 flight hours—on average an engine fails in flight once every 30 years.

The Wasp Major R-4360 air-cooled piston engine used on the Boeing 377 (above) needed an overhaul every 1,000 hours; today, the popular CFM56 jet engine (below) can go 20,000-40,000 hours between overhauls.

Grahic Jump LocationThe Wasp Major R-4360 air-cooled piston engine used on the Boeing 377 (above) needed an overhaul every 1,000 hours; today, the popular CFM56 jet engine (below) can go 20,000-40,000 hours between overhauls.

That reliability has changed the way airlines and aircraft manufacturers operate. In February, for instance, my wife, Liz, and I flew in a twin-engine Boeing 777 over open ocean on an eight-hour flight from Los Angeles to Papeete, Tahiti. The aircraft had to, meet the Extended-range Twin-engine Operation Performance Standards, or ETOPS. (Engine company engineers sometimes colloquialize ETOPS to “Engines Turn or Passengers Swim.”) ETOPS certification applies to twin-engine jets on routes with diversion times of more than 60 minutes for single-engine flying time (in the event of a failure of one engine) to the nearest suitable airport.

During the 1990s, engine companies such as Pratt & Whitney, Rolls-Royce, and General Electric carried out extensive engine component testing to meet ETOPS certification. Operational data showed that inflight engine shutdowns were most frequently caused not by the failure of gas path components (disks, blades, and stators), but by problems with engine ancillaries such as fuel control components and exterior engine case tubing. Thus, some ETOPS test programs involved mounting engines on shaker tables, to reveal weak points in engine ancillaries, under sustained vibrational loading.

The Boeing 777 entered service in 1995 with ETOPS certification and currently can operate on some routes with as much as a five and a half hour diversion time for a single-engine flight. Remember, the Stratocruiser ditched in the ocean with two working engines. Since aircraft operating expenses decrease by reducing the number of engines, twin-jet-engine planes have made intercontinental trijets (such as the L1011 and MD-11) obsolete, and have cut into the market for four-engine planes like the Airbus 340.

The reliability of jets and the availability of unmanned weather buoys (and later, satellites) also eliminated the need for weather ships.

The last U.S. Coast Guard weather ship left service in 1977, although one Norwegian ship continued duty until 2010.

The technological success of the commercial jet engine has changed airline operations—and the aircraft built to serve them—in other ways. For many years, 40 to 60 percent of airline operating expenses have been jet fuel costs. Airlines tried all sorts of strategies to reduce fuel costs, such as locking in prices on long-term fuel contracts as a hedge against price spikes, but they also had a keen interest in ways to reduce overall consumption.

The reliability of modern gas turbines enable twin engine aircraft, such as this one on final approach to Hong Kong International Airport, to operate on routes that take them more than 1,000 miles from the nearest emergency landing strip.

Image: Altair78

Grahic Jump LocationThe reliability of modern gas turbines enable twin engine aircraft, such as this one on final approach to Hong Kong International Airport, to operate on routes that take them more than 1,000 miles from the nearest emergency landing strip.Image: Altair78

Major engine manufacturers responded to that pressure. Both Pratt & Whitney's PW1100G geared fan engine and the LEAP 1A engine from CFM International (the joint venture of General Electric and Snecma) promise a reduction of about 15 to 18 percent in fuel consumption. The reception of these engines by the airlines has been so positive that airframe manufacturers Airbus and Boeing plan to offer essentially new versions of existing single-aisle, narrow-body aircraft that can accept the high-efficiency engines. There is even talk of Airbus launching an A380neo, a re-engined version of its wide-body, double-decker 500-passenger aircraft.

Aviation Week and Space Technology estimates that Emirates, the Dubai-based airline that's a major A380 customer, spends $40 million per year on fuel for each of its A380s. If an engine upgrade resulted in a conservatively estimated 10 percent fuel efficiency gain Emirates would get a fuel savings of about $4 million per aircraft per year, plus some maintenance cost gains that new engines bring about.

That's just part of the calculus that enters the decision-making process in what we’ll call the commercial aircraft gas turbine business, the largest of the five market segments that make up the gas turbine industry.

And that business was basically at full thrust in 2014. To meet the demand for its new geared fan engine, for instance, Pratt & Whitney has installed and opened up a completely new horizontal assembly line in its Middletown, Conn., plant.

Meanwhile, CFM International delivered 1,560 CFM56 engines to airframe companies, a new annual record for this 30,000-pound thrust, top-selling aircraft jet engine. An astonishing 23,000 and change have been sold in 36 years.

Forecast International of Newtown, Conn., provides a financial picture of the gas turbine industry, its history, current state, and forecasted future. The company, using its computer and extensive data base, has computed the value of gas turbine manufacturing production from 1990 to 2014, and has projected values to 2029. (FI considers production figures to be more accurate than reported sales.)

The worldwide production of gas turbines includes the commercial and military aviation markets, as well as non-aviation markets for electrical generation, marine applications, and mechanical power (mostly for driving natural gas pipeline compressors). FI's analysis shows that the value of production of gas turbines worldwide was $82.5 billion for 2014, up from $77.9 billion in 2013. FI's predictions show continued growth, with the global market increasing to $108.9 billion (in 2015 dollars) by 2026, an increase of 32 percent over 2014.

Aviation gas turbines make up the largest segment, totaling $57.4 billion last year, which represents about 70 percent of the gas turbine market. Within the total aviation market, engines for commercial aircraft accounted for 85 percent, with a 2014 total value of production of $49.1 billion. The remaining $8.3 billion of production was intended for military aircraft, such as the Lockheed Martin F-35 Joint Strike Fighter and the Boeing C-17.

The non-aviation gas turbine market, with a value of production for 2014 of $25.1 billion, is characterized by a particular vitality—and volatility.

Utility electrical power gas turbines make up by far the largest portion of the non-aviation market, some $21.1 billion last year. As FI's value-of-production history shows, the electric power gas turbine market had one wild swing in 1999-2002 when electrical utility deregulation caused a short-lived fever in gas turbine power plant construction. Since then, the market has shown a steady recovery, with FI predicting a value of production of $26.7 billion in 2027, though that will still be below the irrational exuberant peak (in 2015 dollars) of $31.8 billion in 2001.

Mechanical drive gas turbines had a value of production of $3.2 billion in 2014, and FI expects this to hold steady in the future, relying on the continuing need for natural gas line compressors and the growing need for liquefied natural gas plants in which gas turbines power the LNG trains. Non-aviation marine power gas turbines had a value of production of $0.8 billion, a small but fairly steady share of the market.

In recent years, gas turbine combined-cycle plants have become key players in the generation of electric power. In combined-cycle plants, heat from the hot gas turbine exhaust enters a heat recovery steam generator (or boiler) to generate steam for a steam turbine, used to generate more electrical power. Thus, one unit of fuel—usually natural gas— goes into the gas turbine combustor, to supply two sources of electrical power.

These combined-cycle plants (the largest are in the 600-700 MW range with gas turbines producing 400-500 MW) have thermal efficiencies that are now exceeding 60 percent, making these the most efficient energy converters mankind has perfected. Additionally, their capital costs are lower than pure steam power plants and far less than nuclear. Now shale gas finds in the U.S., made accessible by hydraulic fracturing and new drilling techniques, have dropped the price of natural gas fuel to low levels comparable to coal.

The U.S. Energy Information Administration recently calculated the levelized cost of these new combined-cycle plants, compared to coal and nuclear. (Levelized cost represents the per-kilowatt-hour cost of building and operating a generating plant over an assumed financial life and duty cycle.) The EIA reported that new gas turbine combined-cycle plants come in as low as 6.3 cents/ kWh, some 43 percent lower than nuclear and 36 percent lower than a coal-fired plant. Some in the power industry complain about the so-called War on Coal or War on Nuclear, but if those industries are under siege, it is from the high efficiency and low cost of these gas-fired combined-cycle plants.

Today, the original equipment manufacturers who supply large gas turbine combined-cycle plants are General Electric, Siemens, Mitsubishi, and Alstom. And soon, the industry will be consolidated further, as GE is in the process of acquiring the power segment of Alstom, thus narrowing the field of large plant OEMs to a Big Three–similar to the threesome in aviation: GE, Rolls-Royce, and Pratt & Whitney–with GE in the lead.

It wasn’t always thus. In the 1970s, the electric gas turbine market was smaller and there were more OEMs, which have been sorted out as efficiencies increased and natural gas prices decreased.

One OEM that dropped out of the electric market was Pratt & Whitney. In the early 1970s, the company's management decided to use the P&W jet engine design system to develop a new efficient heavy frame 100 MW electric power gas turbine.

At the time, advances in jet engine design hadn’t been extensively incorporated into the design systems of the non-aviation OEMs. For instance, General Electric had a then-current corporate policy encouraging its Schenectady-based nonaero Power Generation Group (producing a Frame 10 series in the 100 MW range) to compete with GE's own Evandale, Ohio, Aircraft Engine Group's aeroderivative engines, used for non-aviation applications.

Pratt's heavy frame engine was called the FT50 and it hit a record (for the time) 34 percent thermal efficiency with its jet engine design gas path. As a young engineer with P&W in 1975, I saw the 36-foot-long FT50 on the assembly floor in the Middletown plant—easy to pick out, as it overshadowed collections of jet engines in surrounding areas. Shortly thereafter the company's management decided to end the multi-million dollar FT50 program it had been partnering with the Swedish company, Stal-Laval. Only one of the engines had been completed.

Hindsight shows that the FT50 was technically well ahead of its time—and competitors. Using Pratt's experience from military jet engines, the FT50 had the first use of non-aviation turbine film cooling. That allowed it to run at turbine inlet temperatures of 2,100 ̊F, much higher than contemporary machines and contributing to its record-breaking 34 percent thermal efficiency.

The FT50 also had Pratt's twin spool design, allowing each compressor and turbine to operate at optimum component efficiency. (Compressor efficiencies were 90 percent—higher than any other non-aviation gas turbine at the time.) And following aviation gas turbine design, the FT50 was constructed in modular form, which enabled the engine to be easily dismantled in days rather than the standard several months, for say, combustor replacement.

The Pratt & Whitney FT50, on the assembly floor in Middletown, Conn., in 1975. The turbine is being installed in Angola.

Image: Don Cleary

Grahic Jump LocationThe Pratt & Whitney FT50, on the assembly floor in Middletown, Conn., in 1975. The turbine is being installed in Angola.Image: Don Cleary

Counterfactuals are always impossible to prove, but had Pratt & Whitney not abandoned its multimillion dollar investment in the 1970s, it might today be one of the Big Three in both the aviation and non-aviation market segments.

Last September I gave a talk at the Stal-Laval plant (now part of Siemens Industrial Turbomachinery) in Finspång, Sweden. There I learned that the sole FT50 gas turbine ever manufactured had been sold to a Swedish utility and had been in operation since the late 1970s. Indeed, it had only recently been decommissioned.

But that wasn’t the end for the FT50. The unit, now about 40 years old, is being installed at a plant in Angola for further electrical generation.

In most cases, sure, new is usually better. But when a piece of technology is well designed and built to last, it can endure and find new uses over and over again.

Copyright © 2015 by ASME
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