This article focuses on the use of gas turbines for electrical power, mechanical drive, and marine applications. Marine gas turbines are used to generate electrical power for propulsion and shipboard use. Combined-cycle electric power plants, made possible by the gas turbine, continue to grow in size and unmatched thermal efficiency. These plants combine the use of the gas turbine Brayton cycle with that of the steam turbine Rankine cycle. As future combined cycle plants are introduced, we can expect higher efficiencies to be reached. Since almost all recent and new U.S. electrical power plants are powered by natural gas-burning, high-efficiency gas turbines, one has solid evidence of their contribution to the greenhouse gas reduction. If coal-fired thermal power plants, with a fuel-to-electricity efficiency of around 33%, are swapped out for combined-cycle power plants with efficiencies on the order of 60%, it will lead to a 70% reduction in carbon emissions per unit of electricity produced.
In a Crowded Marketplace, companies must differentiate themselves—even if that means stretching the truth a bit. Manufacturers of snack foods often trumpet healthy aspects of their product—Fat Free! Gluten Free!—even if it is full of added sugars and preservatives.
Airlines aren’t much different. In 1964, Eastern Airlines began a service it called “Whisperjet” using Boeing 727s with rear-mounted engines. “Quiet as a library,” one of the television ads promised, right after running through the menu choices of lobster Newburgh and filet mignon.
The food may have been fancy, and for those riding in first class, engine noise may have been reduced. Somewhat. But the Pratt & Whitney JT8D-200 engines themselves were every bit as deafening as every other jet engine of that era.
Fifty years later, things have changed. The Whisper Jet brand name is back, even if Eastern Airlines is long gone. It's being revived by Porter Airlines, the major carrier out of Billy Bishop Toronto City Airport. The popular airport, which handles 2 million passengers annually, has had a city-imposed ban on jet engine use for scheduled airlines since 1983. They are too noisy for the downtown location.
Porter has petitioned Toronto authorities to exempt from the ban the 12 Bombardier CS100s it has ordered. The 107-passenger CS100s are powered by two of P&W's new PW1500G geared turbofan engines. Although the engine provides 20,000 pounds of thrust, due to its large-diameter, geared-down, lower-rpm fan, less fan noise is generated. The resulting lowered-velocity exiting fan bypass air provides for greatly diminished jet noise. The characteristic turbofan whine is gone, replaced instead by a “whoosh”.
All told, the GTF puts out half the noise of similarly sized jet engines, and thus a sound footprint only a quarter as large. (There is also a 16 percent reduction in fuel consumption.) Some engine people claim that the GTF engines should be even quieter than the currently permitted Porter turboprops. These would be Whisper Jets that could live up to the name.
Here one can see that noiselessness could mean big money. If approved, Porter Airlines Whisper Jets could offer direct flights to Vancouver, Florida, or the Caribbean, now beyond the reach of Porter's short-haul turboprops. Airport staff estimates that introduction of such GTF flights could double passengers handled at Billy Bishop, to well over 4 million annually.
Pratt & Whitney's geared fan PW1000G family will also be powering other new single-aisle, narrow-bodied aircraft in the coming years. These include the Airbus 320neo, the Mitsubishi MRJ, the Embraer E-Jet, and the Irkut MC-21. When airport neighbors and passengers—especially those at congested hubs like London's Heathrow—hear the marked reduction in takeoff and landing noise from geared fan turbojets, one can speculate there will be more public pressure to quiet other jet aircraft.
The Wisdom of a Gear Box for a jet engine fan wasn’t always obvious. For instance, the keynote session of IGTI's 2005 Turbo Expo in Reno featured the president of Pratt & Whitney, who reported on progress with the geared turbofan after ten years of development. During the discussion afterwards, retired CEOs from rival GE Aircraft Engines and Rolls-Royce both stated that based on their experience such systems were to be avoided. The consensus was that Pratt was following a dead end.
That consensus has now reversed. Rolls-Royce recently announced that the company will pursue large geared turbofan designs for their next generation engines for the 2020s. And with its GTF, Pratt is taking aim at the engine maker that dominates the single-aisle, narrow-body market: CFM International.
Jointly owned by GE Aviation and SNECMA, CFM International has sold some 23,000 CFM56 engines in the last 35 years. These engines, in the 30,000 lbt range, power most of the Boeing 737 and Airbus 320 families, the current duopoly aircraft of SANB. Both Boeing and Airbus are projecting that SANB will be a $2 trillion dollar market for the next 20 years, accounting for more than 23,000 airplane deliveries.
CFM International is countering P&W's GTF with LEAP (Leading Edge Aviation Propulsion), a high-bypass turbofan successor to CFM's very successful CFM56. The LEAP family is undergoing flight testing in 2014, and is scheduled for full FAA certification in 2015-16. The engines will then be entered into service on the Airbus 320neo, the Boeing 737 MAX and the Comac 919.
The LEAP engine will have a 15-to-16 percent reduction in fuel consumption, compared to the current CFM56. A higher bypass ratio and a higher compression ratio contribute to lower fuel consumption. LEAP's larger diameter fan is constructed of carbon fiber composites for light weight and durability, as is the encircling fan case.
LEAP will also be the first commercial engine using ceramic matrix composites in its hot section. These composites, consisting of ceramic fibers embedded in a ceramic matrix, can be made as strong as metal and can withstand temperatures higher than heavier nickel-based superalloys. Endurance LEAP engine testing is being carried out to validate the new hot section technology, with over 5,000 cycles completed to date.
These Two Competing turbofan engines, the GTF and the LEAP, are part of a much larger global gas turbine market, which is broken down into two segments, those manufactured for aviation and those for non-aviation applications.
This year, 2014, marks the diamond jubilee for both segments. 1939 was a pivotal year in many fields: Hollywood produced both Gone With the Wind and The Wizard of Oz; The Grapes of Wrath and Finnegans Wake were both published; fission was discovered and nylon was introduced. And with gas turbines, there were two seminal events in 1939. The first non-aviation gas turbine was completed and tested under full load on July 7, 1939, by the Swiss firm, Brown Boveri; it powered a 4 MW electrical generator for installation as a power plant in the Swiss city of Neuchâtel. (A new book, Gas Turbine Powerhouse by Dietrich Eckhardt, details the history of this first gas turbine power plant, Brown Boveri, and a multitude of other gas turbine projects.) The next month saw the first aviation gas turbine powered flight take place over the Baltic Sea. That first jet plane, the single-engine He178, flew out of the Heinkel Aircraft Company airfield at Rostock-Marienche, Germany, on the morning of August 27. A few days later, the German army invaded Poland.
Over the intervening 75 years, gas turbines have become a major energy converter, both in aviation and non-aviation applications. One way to gauge their influence is to look at recent gas turbine industry financial history. Using computer models and an extensive data base, analyst Bill Schmalzer of Forecast International in Newtown, Conn., has provided the values of gas turbine manufacturing production from 1990 to 2013, and has projected values to 2028. (FI considers value of production figures to be more accurate than reported sales figures.)
Schmalzer reports that the value of production for gas turbines worldwide was $65.7 billion in 2013, up from $61.7 billion for 2012. By 2028, that's projected to increase to $88.7 billion in constant dollars, up some 35 percent from 2013. FI's value of production history and predictions do indeed show that the gas turbine has been and will be a global growth industry.
FI's gas turbine value-of-production history and predictions from 1990 to 2028 show a steady, essentially monotonic growth for the aviation segment, which is now two thirds of the industry. In 2013, the value of production of gas turbines for commercial aviation was $37.9 billion, while $6.3 billion was for military jets.
When one considers there are about 19,500 airplanes in the worldwide air transport fleet and almost all are powered by gas turbines, it is obvious why commercial aviation dominates the aviation engine market. The much smaller military gas turbine market, however, is crucial to the development of commercial gas turbines.
From the first flight of the He178, the very first jet planes were military fighters, from which commercial engines were developed. Right now, one of the most technologically advanced jet engines is the Pratt & Whitney F135, which powers the Lockheed Martin F-35 Joint Strike Fighter. Based on past history, the technology breakthroughs in the F135 should eventually lead to improved commercial gas turbines.
The Other Side of the Industry-gas turbines for electrical power, mechanical drive, and marine applications-had a value of production in 2013 of $21.5 billion.
Marine gas turbines are used to generate electrical power for propulsion and shipboard use. For instance, the cruise ship Queen Mary 2 has two General Electric LM2500 gas turbines, each providing up to 36 MW, in addition to its four diesel engines. The LM2500 is derived from General Electric's CF6 turbofan engine, used on Boeing's 747 and 767.
Natural gas pipelines provide a large market for mechanical drive gas turbines. To make up for frictional pressure losses in natural gas flow, compressor stations are located about 50 miles apart along a pipeline. The compressors are powered by gas turbines, which use pipeline natural gas as fuel.
But according to the data from Forecast International, about 85 percent of the value of production of non-aviation gas turbines is used for electrical power purposes. That segment of the gas turbine market can be volatile, as evidenced by a short-lived spike in the value of production of gas turbine electrical generating sets in 2001, caused by irrational market exuberance at the onset of electric utility deregulation. Post-spike behavior has shown a steady recovery and growth in electrical generation markets with the value of production in 2005 doubling by 2013 to $18.3 billion.
Combined-cycle electric power plants, made possible by the gas turbine, continue to grow in size and unmatched thermal efficiency. These plants combine the use of the gas turbine Brayton cycle with that of the steam turbine Rankine cycle. (They should more accurately be termed a combined power plant, because the thermodynamic cycles are not combined, but separate.) The gas turbine hot exhaust gases are used to generate steam to drive a steam turbine, with both turbines driving generators to produce electricity from one unit of fuel (usually natural gas), rather than two units, if separate.
General Electric just announced its new H-class combined-cycle air-cooled gas turbines, the 9HA.02 and the 7HA.02. Gas Turbine World reports that the air-cooled 9HA.02 will have a gas turbine output of 470 MW, a combined-cycle output of 710 MW at a quoted thermal efficiency of 61.2 percent. If reached, that efficiency mark will best the current record holder, a combined-cycle plant at Irsching, Germany, powered by a Siemens SCC5-8000H, which with a combined-cycle efficiency of 60.75 percent is the most efficient heat engine ever run.
As future combined cycle plants are introduced, we can expect higher efficiencies to be reached. We’ll need every gain we can get.
This year's Environmental Protection Agency Annual Report shows there has been a remarkable 10 percent drop in U.S. generated greenhouse gases, between 2005 and 2012. One major contributing factor to this reduction has been the nation's switch from carbon-rich coal to low-carbon natural gas in electricity generation.
Since almost all recent and new U.S. electrical power plants are powered by natural gas-burning, high-efficiency gas turbines, one has solid evidence of their contribution to the greenhouse gas reduction reported by EPA. This has led EPA to propose new fossil-fuel power plant regulations, which assume a baseline for the electricity sector in which new generation capacity comes primarily from modern, efficient combined-cycle, gas-fired turbine plants.
How much of an improvement would these plants provide? Natural gas itself has half the carbon emissions of coal on a per-Btu basis, according to the Energy Information Agency. So if coal-fired thermal power plants, with a fuel-to-electricity efficiency of around 33 percent, are swapped out for combined-cycle power plants with efficiencies on the order of 60 percent, it will lead to a 70 percent reduction in carbon emissions per unit of electricity produced.
Here's a case where the marketing superlatives are appropriate. Gas turbines really are a modern wonder.