Japanese Airliner to Introduce PW's New Engine Technology

posted: 09 October 2007 04:50 pm ET

: Because the reduction gears in Pratt & Whitney's new Geared Turbofan engine drive the fan independently of the low-pressure compressor and turbine stages, the fan can revolve more slowly and can have a larger diameter. In turn, the blades can be larger and lighter. The fan in the Geared Turbofan will have only 18 blades, each with an advanced aerofoil shape. Previous large-turbofan engines had approximately twice as many fan blades. Credit: Pratt & Whitney
: In Pratt & Whitney's Geared Turbofan the gearbox, located just behind the fan and driving it independently of the low-pressure compressor and low-pressure turbine, allows the comrpessor and turbine stages to rotate far faster than they would if they remained coupled to the fan. This makes each stage more efficient, allowing Pratt & Whitney to reduce the number of compressor and turbine stages, thus reducing the number and weight of components needed in the engine and cutting its operating costs. Credit: Pratt & Whitney
: The reduction gears in the gearbox located behind the fan in Pratt & Whitney's Geared Turbofan engine effectively de-couple the fan from the low-pressure compressor and low-pressure turbine stages. Even though the low-pressure spool, powered by the low-pressure turbine stages, still is the motive force for the fan, the gears allow the fan to rotate more slowly than the turbine and compressor stages, making all of the stages work more efficiently. Credit: Pratt & Whitney

Pratt & Whitney's next-generation commercial jet engine will notch up its first sales on an airliner built in Japan.

Mitsubishi Heavy Industries Ltd. (MHI) has chosen Pratt & Whitney's two-spool Geared Turbofan engine to power the Mitsubishi Regional Jet (MRJ) that the Japanese company expects to launch next spring. Pratt & Whitney has been developing geared turbofan(GTF) technology for nearly the past 20 years.

"We believe the Pratt & Whitney Geared Turbofan engine offers a technological breakthrough that will provide the best economy and performance for the Mitsubishi Regional Jet," said Kazuo Tsukuda, president of MHI. "The MRJ will offer airline customers best-in-class fuel efficiency and environmental performance, with superior cabin comfort."

MHI initially plans to offer the MRJ in two fuselage lengths. The shorter-fuselage variant will seat 70 passengers, with the longer-fuselage variant seating 90 passengers. The Japanese company expects there will be global demand for some 5,000 commercial aircraft in the MRJ's size class over the next 20 years.

Pratt & Whitney (P&W) will provide a 15,000-pound-thrust-class version of its Geared Turbofan engine for the 70-seat MRJ and a 17,000-pound-thrust-class version for the 90-seat jet, said P&W spokeswoman Jennifer Whitlow.

MHI's launch schedule for the MRJ envisages the aircraft entering commercial service in early 2013. This fits in well with P&W's own development schedule for the Geared Turbofan, said Whitlow.

After accelerating its GTF development program during the last few years, P&W said it was prepared to launch the Geared Turbofan officially in 2008 and for the engine to enter service in 2013. The company has spent approximately $1 billion on GTF development over the past 20 years, and says it is spending more than $100 million this year alone on the technology as it moves toward the first flight-test of its Geared Turbofan engine.

Test schedule

P&W has already conducted extensive testing of GTF components and systems on rigs, and the company now is assembling a demonstrator Geared Turbofan engine at its plant in East Hartford, Conn. P&W expects to ground-test the demonstrator engine before the end of this year.

It plans to start flight-testing the Geared Turbofan in mid-2008. Given that new large-turbofan engines usually have "about a five-year development cycle," the manufacturer expects its new engine to be ready to enter service early in 2013 along with the MRJ, said Whitlow.

In existing two-spool turbofan engines, the huge front-end fans that provide most of the thrust (in the form of cold "bypass" air that isn’t mixed with fuel and burned in the combustor) are driven by the engines' low-pressure spools at the same rotation speeds as the low-pressure compressor stages and low-pressure turbine stages.

This arrangement isn’t optimal for any of the engine stages in terms of fuel-efficiency and noise and environmental performance.

However, in a two-spool GTF engine, a state-of-the-art gearbox is attached to the front end of the low-pressure spool. The reduction gears allow the fan to operate independently of the low-pressure compressor and low-pressure turbine stages.

Slower fan rotation speed

As a result, the fan can operate at a slower speed than in a conventional turbofan, producing a lower noise level. Because the noise level is significantly reduced, the fan's blade-tip speeds can be increased to an extent without creating noise problems, so the engine's diameter can be made larger. This allows the fan to achieve a higher bypass ratio for greater efficiency and fuel economy. The slower fan rotation speed also lets the manufacturer make each fan blade lighter.

At the same time, the low-pressure compressor and turbine can operate at higher speeds than if they were linked directly to the fan, allowing these stages to achieve their best efficiency. At faster rotation speeds, the turbine can power the compressor and fan with fewer stages. This reduces the number of parts needed and thus the weight of turbine components, reducing operating costs. The compressor also benefits in requiring fewer parts, which further reduces component weight and operating costs.

Competing engine manufacturer Rolls-Royce decided back in the late 1960s to develop a three-spool design for its first high-bypass turbofan engine, the RB.211, with the third spool driving the fan independently of the low-pressure compressor and low-pressure turbine. The UK company has adopted three-spool designs for all its subsequent turbofan engines -- the latest being the Trent 900 for the Airbus A380 and the Trent 1000 for the Boeing 787, with the Trent XWB to come for the Airbus A350 XWB. Rolls-Royce maintains its three-spool architecture achieves similar noise and fuel-efficiency benefits to those of the geared-fan approach.

Other technological advances incorporated

Pratt & Whitney will incorporate other technological advances into its Geared Turbofan engine. Among them are its next-generation TALON (Technology for Advanced Low NOx) low-emissions combustor, an advanced high-pressure compressor, and a suite of high-pressure turbine technologies.

The company's rich-quench-lean (RQL) TALON combustor uses advanced fuel/air atomizers and mixers, metallic liners, and advanced cooling management to lower emissions of oxides-of-nitrogen during take-off, high-altitude cruise, and landing. P&W is developing the newest "TALON X" version of the combustor in partnership with NASA. The TALON X combustor already has demonstrated extremely low emissions, smooth ignition both at sea level and in high-altitude conditions, and excellent reliability, the manufacturer said.

Pratt & Whitney's high-pressure compressor technology features a compact, high-work system with integrally bladed rotors and cantilevered stators. The Geared Turbofan's high-pressure turbine uses advanced aerodynamics, cooling management, and sealing technologies. P&W also has developed new thermal barrier coatings, which it expects will increase engine durability and time on-wing significantly.

More than 17,000 Pratt & Whitney engines are installed on jet and turboprop airliners throughout the world. The company also is a partner in two joint ventures that manufacture commercial aircraft engines: International Aero Engines, which makes the V2500 for the Airbus A320 family of aircraft, and the Engine Alliance, whose GP7200 engine is one of the two engine choices for the Airbus A380.