GUY NORRIS / LOS ANGELES
European and US researchers are determined to ensure next-generation engines are kinder to the environment
Progress towards the next generation of efficient, environmentally friendly aircraft engines is gathering speed on both sides of the Atlantic, with NASA defining a demonstrator "road map" and European efforts well into initial rig testing.
NASA's Ultra Efficient Engine Technology (UEET) programme, now nearing the end of its second full year, is tasked with developing and handing-off revolutionary turbine engine technology for everything from supersonic business jets to auxiliary power units. As part of this effort, UEET seeks dramatic reductions in CO2 emissions based on an overall fuel savings target of up to 15%. It is also chartered with developing technologies for a 70% cut in NOx emissions at take-off and landing, as well as technology to prevent significant impact on the ozone layer during cruise.
Following a similar theme, the European Commission's Efficient and Environmentally Friendly Aircraft Engine (EEFAE) project aims to cut emissions and increase efficiency, while also cutting costs. EEFAE is in two major parts - a near-horizon Affordable Near Term Low Emissions (ANTLE) validation vehicle, and a longer-term Component Validation for Low Emission Aero Engine (CLEAN).
ANTLE, targeted at 40,000-50,000lb thrust (180-220kN) engines primarily for future widebody aircraft, aims for a 12% cut in fuel consumption relative to 1990s technology. It also seeks a 12% cut in CO2, 60% lower NOx (relative to ICAO 1996 standards), and major cost and life-cycle expense reductions.
Coming CLEAN
CLEAN, aimed at technology for future narrowbody engines in the 2020 time frame, plans to reduce CO2 emissions by 20% and NOx by up to 80%.
The immediate focus for UEET is to define which and how many demonstrators to develop. To work out the answers, it is holding trade study talks with its industrial and US government agency partners, and plans to have the map inked in over the next few months. "We will also be working more closely with the Department of Defense to minimise the number of demonstrators," says Joseph Baumeister, project manager at NASA Glenn Research Center, from where UEET is managed.
The actual drawing of the road map is not so easy because of the widely differing needs of the various UEET participants. However, simply defining arbitrary low- and high-thrust demonstrators is not a "big win situation", says Baumeister.
"We're getting the industry people to see how they'd like to execute them." But the task is made even more difficult because "they all have different baseline engines and vehicles, and they all have different suites of technologies they want to run. Plus, NASA has to work out how to complement all this with its in-house technologies and other efforts such the Quiet Aircraft Technology Programme, and stay in concert with the seven UEET priorities".
These priorities are general technology areas: propulsion system integration and assessment; emissions reduction; highly loaded turbomachinery; engine materials and structures; propulsion-airframe integration; intelligent propulsion controls; and integrated technology demonstrators. On top of all this, the UEET planners must also wait for each company to decide what it can, or cannot, let the other partners see.
UEET partners include General Electric, Honeywell, Pratt & Whitney and Williams International as well as Allison Advanced Development and its parent company, Rolls-Royce. Boeing, Lockheed Martin and Northrop Grumman are also involved. Part of the definition process involves working out cost sharing. "We can't have eight engine demonstrators in the programme - we just can't afford that," says Baumeister.
The final map could be drawn by February depending on how much co-operation develops within the enlarged UEET partner group. "Within a month we will get a better idea of the level of co-operation with industry," says Baumeister, who points out initial proposals have been fielded with GE and R-R. "They are the precedents. They are 'pinging' their management and, maybe in January, we will get feedback from them. Early next year we will also sit down with the US Air Force and present it with what we'd like to do."
Talks with the DoD, particularly the USAF, will focus on how to fill the void in supersonic engine research left after the Defense Advanced Research Projects Agency (DARPA) decided to focus the Quiet Supersonic Platform (QSP) project on airframe studies. The obvious choice is an adaptation of the USAF's versatile affordable advanced technology engine (VAATE) project, with which NASA is linked. To help pave the way, NASA has brought three ex-Lockheed SR-71 P&W J58 engines out of mothballs and fired them up at Dryden Flight Research Center, California. The Mach 3-capable engines make "good hot gas generators" and could be used for testing in areas such as propulsion control, says Baumeister. A number of used P&W F119 engines from the F-22 flight-test programme have also "become available".
Meanwhile, component tests continue. Further evaluations with GE of an advanced ceramic matrix composite (CMC)-lined combustor and aspirating seal technology are planned for next year. Success in the CMC area is critical to reducing NOx as only sustained high combustion temperatures of 1,480°C (2,700°F) make this goal achievable. Aspirating seals are intended to replace traditional labyrinth seals, and could cut fuel consumption by 1.86%.
Geared-fan propulsion
Other tests are also under way with P&W on highly misaligned sealing and non-interrupted lubrication system technology. Both are crucial foundations for geared-fan propulsion, which is "pretty high on P&W's priority list", says Baumeister.
In Europe, ANTLE rig testing is under way and on track for the first run of a full engine in early 2004. "We are in the final throes of design freeze - as far as hardware goes, we're well down the line in terms of forgings and long-lead items," says Steve Morgan, chief engineer for ANTLE at R-R, which leads the eight-member team. Other ANTLE members are R-R Deutschland, ITP of Spain, FiatAvio of Italy, Sweden's Volvo, Techspace Aero of Belgium, France's Hispano-Suiza and Goodrich (ex-TRW Lucas) of the UK.
Supporting rig test work began in 2001 with a turbine rig and is to increase in coming months. R-R plans this month to begin rig tests of a full single annular combustor. The direct-injection, staged-combustor design passed sector tests earlier this year.Rig tests of a four-stage low-pressure turbine (LPT) developed by ITP are due to start around April 2003. This is several months later than originally planned, and is part of an overall rescheduling of the ANTLE and CLEAN milestones to reflect "issues of phasing, availability of testbeds and things like that", says Morgan. However, the timescale remains "broadly in line with the original programme intent, and we are targeting technology readiness levels that are compatible with entry into service around 2008," he adds. Final details of the revised ANTLE/CLEAN schedule are expected to be agreed with the EU's EEFAE committee in March.
The baseline ANTLE demonstrator uses the Trent 500 as a foundation. but "everything from the IPC [intermediate pressure compressor] back will be new", says Morgan, who stresses ANTLE is "not an engine per se, but a rig - it's about making sure the tools we used to design it are validated".
As well as the combustor and advanced LPT, the demonstrator will incorporate a five-stage, three-dimensional aerodynamic-designed high-pressure (HP) compressor with integrated blisk (bladed disks) rotors, a low-parts count HP turbine with 25% fewer parts than current designs, and a more efficient intermediate pressure turbine. Other key technology areas include a "fabricated" tail-bearing housing from Volvo, as well as an advanced control system, enhanced oil system and new gearbox.
As with the US plan, ANTLE aims to do more with less. So loading per stage will be much greater than current engines and the overall engine pressure ratio will be much higher than 40:1, says Morgan.
In another parallel with the US activities, ANTLE does for R-R what UEET does for GE and P&W in terms of preparations for the next generation leap. In the case of GE, the UEET map leads to its newly revealed Generation X and Y "intelligent" engine plans. For R-R, ANTLE in particular is a launch platform for the UK company's "Vision 10" next-generation engine plan.
With the current emphasis on efficiency, it seems certain the next generation will truly be "green machines" compared with their roaring, smoky forebears.
Source: Flight International
