Ernie Arvai posted this article on the Pratt & Whitney GTF engine earlier today at GLGNews. For convenience, this article is also reproduced below.
Pratt and Whitney’s new PW1000G series geared turbofan engine, which will power the Bombardier CSeries, Mitsubishi Regional Jet and Irkut MS-21 narrow bodies and is being considered for application on a new model from Embraer, as a new engine option for the Airbus A320 and either as a re-engining or used on a replacement model for the Boeing 737. This engine promises to change the market dynamics in the commercial aircraft engine marketplace, and Pratt & Whitney will market this engine directly, rather than through its IAE joint venture with Rolls Royce, Japan Aero Engines and MTU. This engine is a game changer and will be introduced on the Bombardier C Series in 2013.
The geared turbofan offers several advantages over conventional turbofans. It’s main fan rotates about 30% more slowly than conventional turbofans, enabling a larger fan diameter while avoiding blade-tip shock waves that degrade performance. With a large fan, a higher bypass ratio is possible which increases efficiency over conventional designs. Combined with the need for fewer stages, lower operating temperatures and other new technologies, Pratt and Whitney has designed the GTF for both efficiency and reliability.
Geared turbofans are not a new invention. The Garrett TFE731 and Avco Lycoming LF502/507 engine families, both now made by Honeywell, are geared turbofans that have accumulated millions of hours in service. While the LF502/507 family was noted for a lack of reliability, the cause of those problems were not due to the gearbox or geared-turbofan design.
Scalability has been a problem for gearboxes, which Pratt & Whitney has solved with a proprietary and patented light weight design that includes a robust lubrication system to ensure long gear life. As a result, the PW1000G can be expanded to 40,000 pounds of thrust (which is the size of 757 engines) and similar technology, scaled upward, could also form the basis for a new wide-body engine offering for the forthcoming Boeing 777 replacement.
While the focus on the GTF has been the innovative gearbox, other new technologies have been introduced that will make this engine the efficiency leader when it reaches the market in 2013. A new core for the PW1000G was developed jointly with MTU, and is optimized for high cycle narrow-body operations. With the gearbox reducing the need for low pressure stages from 6-7 normally associated with an engine of this type to 3, the net result is about 1,500 fewer blades than a conventional engine, with corresponding maintenance savings.
The high pressure compressor utilizes single-piece integrated bladed rotors, or “blisks”, which also provide maintenance savings. An advanced combustor features a “floatwall” of liners that expand and contract independently, which combined with a rich-quench-lean combustion cycle will prevent nitrogen oxides from forming. PW’s GTF will be the “greenest” engine on the market, which will be increasingly important as emissions become taxed.
The net result of this combination of technologies is that the 1000G will run cooler than other engines. Because heat causes wear, PW expects longer component life and durability than its more conventional technology competitors.
How Much More Efficient is the GTF?
The PW1000G is expected to enter service in 2013 about 12% more efficient than current competitors, but PW expects that will grow to 22% per year as the engine matures during the first decade in service, with kits to retrofit early models to higher efficiency configurations.
How will the GTF stack up against the competing Leap-X engine from CFM International, the joint venture of SNECMA and GE? Preliminary design information about the Leap-X indicates that it has changed its architecture from the high-cycle and durable design in the CFM-56 to utilizing designs similar to the more fuel-efficient concepts from the GE-90 and GEnx wide-body engines powering the 777 and 787. The Leap-X should be about 15% more efficient than today’s engines when introduced in 2015-16, about the same level as the GTF. But there may be a significant difference.
The GTF has been designed from the ground up for durability and high cycle, narrow-body operations with 20% lower maintenance costs. The Leap-X, from the preliminary information we have seen, appears to be moving away from the design of the current industry leading CFM-56 offering to less robust but more fuel efficient design concepts more typically associated with wide-body engines that operate fewer daily cycles.
While fuel economy can be achieved with wide-body engine concepts, they are typically not applied to narrow-body engines because of the difference in operating environments — wide body airliners tend to take off and cruise for 8 hours – versus 1-2 hours for narrow body models. Because take-offs require the highest thrust, narrow-body engines must be engineered to be much more durable. While we have no doubt that CFM can meet its fuel economy goals, the critical question is whether it is trading off reliability to get there.
The GTF is more than simply a gearbox, and is introducing several important new technologies into the narrow body engine market. Pratt & Whitney appears to have engineered a winner. We expect the PW1000G to be chosen for the new Embraer model, as an option for the Airbus A320NEO family, and for either a re-engined 737 or 737 replacement model from Boeing. Pratt & Whitney, once thought moribund in the commercial market after years of decline, is emerging as a resilient player through technology innovation, and will certainly gain a significant increase in its market share for narrow-body aircraft engines over the next two decades.