As airframe manufacturers continue to develop the next generation of commercial and business jets, engine OEMs have been tasked with incorporating performance enhancements to make their products tighter on fuel burn, more environmentally sensitive, quieter and less maintenance intensive than those in service.

Improvements in engine performance are expected to be far more than incremental. For example, the "2008 Addendum To The Strategic Research Agenda, Advisory Council for Aeronautics Research In Europe" (ACARE) sets a goal for European airlines to reduce carbon dioxide emissions by 50%, nitrogen oxide by 80% and perceived external noise by 50% by 2020. At the same time, the industry must make what the council calls "substantial progress towards green manufacturing, maintenance and disposal" by 2020.

ACARE's objectives have not been lost on the engine makers. Alan Newby, Rolls-Royce chief engineer of future programs, says the OEM is trying to decrease fuel burn through two parallel research tracks--propulsive efficiency and thermal efficiency.

Pratt & Whitney's PurePower geared turbofan engine's turbine stages are made of a super nickel alloy and the compressor stages are titanium, while the gear is steel. Credit: PRATT & WHITNEY Propulsive efficiency targets increases in the engine's bypass ratio, because the higher the ratio, the greater the fuel efficiency.

"The current generation of engines normally has a bypass ratio of 10 to 11, compared to a ratio of 4 to 5" for earlier engines, Newby notes. "At Rolls-Royce, some of our research and development effort is concentrated on the open rotor design concept, which could deliver a bypass ratio of 50--or five times greater than it is today." (See sidebar p. 30 for more on open-rotor technology.)

This technology, says Newby, has the potential to improve engine fuel efficiency by as much as 30% relative to today's engines. "At the same time, we'd gain about a 30% reduction in CO2 emissions," he adds.

Thermal efficiency, Newby reports, will improve with increased engine temperatures and greater overall pressure ratios. To achieve that, Rolls-Royce is developing improved materials technology that targets the metal alloys and thermal barrier coatings to be used in turbine blade fabrication. The ceramic-based coatings would shield the turbine blades from the high operating temperatures required to increase thermal efficiency, which Newby estimates at 1,800 to 1,900 degrees Kelvin (2,780.33 to 2, 960.33 degrees F).

"The high temperature materials technologies we are developing will be applicable to all future engines," says Newby. "That includes large-engine developments, such as the Trent XWB, as well as a V2500 replacement engine for 150-seat aircraft. This technology can be applied to either improve performance by reducing cooling air requirements at a given life or to increase on-wing life and reduce maintenance costs for a given level of cooling air. Today, the airframe OEMs and their customers want to see a big reduction in operating costs," from fuel to maintenance.

Geared Turbofan

Pratt & Whitney believes that technologies in its geared turbofan engine will revolutionize engine performance. It formally launched the new product family in 2008, after some 20 years of research and development. The 21,000-23,000-lb. thrust PW1500G and the 15,000-17,000-lb. thrust PW1200G geared turbofan initially will be applied to short-range narrowbody jets. Bombardier's 100-149-seat CSeries jet is the PW1500G launch customer, and Mitsubishi Aircraft's 70-100 seat MRJ is the first application for the PW1200G. Service-entry dates for the two aircraft are 2013 and 2014, respectively.