Study targets quieter and cleaner engines
Researchers across Europe have made substantial progress in their pursuit of the cleaner, more fuel efficient engines that will be needed if air traffic is to continue growing without its environmental impact becoming unacceptable.
The four-year, ?91 million ($118 million) VITAL research program looking at environmentally friendly aircraft engines is part of a continent-wide effort to meet the demanding goals set at the beginning of the decade by the Advisory Council on Aeronautical Research in Europe (ACARE). They include reductions of 50 percent in carbon dioxide (CO2) and 80 percent in oxides of nitrogen (NOX) and other emissions, along with a halving of perceived noise. Engine targets are a 10 dB reduction in noise per operation, a 60- to 80-percent cut in NOX and a 20-percent reduction in fuel consumption.
VITAL in turn is aiming to achieve reductions of six decibels per aircraft operation in noise along with a 7-percent cut in fuel burn and, hence, CO2 emissions. And with several months of testing still to be completed, the program has already come close to meeting them.
At the concluding conference in Budapest in March, program coordinator Jean-Jacques Korsia of Snecma said tests will continue until the end of the year, “but the results already available leave us confident of achieving the VITAL objectives.”
The baseline engines for the research were the CFM International CFM56 and Rolls-Royce Trent 700, which represented the state of the art when the ACARE targets were formulated at the beginning of the century. The work was structured around conceptual direct drive, geared and contrarotating turbofans for both long- and short-range aircraft, making a total of six engine configurations.
It involved 53 manufacturers, research institutes and universities, including engine makers Rolls-Royce, MTU, Avio, Volvo Aero, Techspace Aero, Rolls-Royce Deutschland and ITP.
The fan was expected to make the biggest contribution, with targets of a six-decibel reduction in externally perceived noise (EPNdB), a 30-percent reduction in weight and a 2-percent improvement in efficiency. The engines had bypass ratios ranging from 10 to 14 and fan diameters from 74 to 123 inches.
A contrarotating fan has already demonstrated increased efficiency of up to two percentage points and a calculated 4 EPNdB reduction in noise, while a 30- percent lighter fan module has passed bird-strike, blade-off and fatigue tests. A direct-drive fan is due to undergo aeroacoustic tests next month.
Other Programs at Work
VITAL itself is just one of the research programs exploring ways to meet the ACARE goals. Next month in Warsaw, for example, researchers will meet to review progress on new aero-engine core concepts (NEWAC). A four-year project launched in May 2006 with a €71 million budget, NEWAC complements VITAL’s work on the low-pressure components and aims to reduce (CO2) emissions by 6 percent and NOX emissions by 17 percent through improvements to the engine core.
Led by MTU Aero Engines and counting Snecma, Rolls-Royce and Avio among its
40 partners, the research focuses on intelligent compressors, improved combustors and integrated heat exchangers. They will find application in four varieties of emerging innovative core engines: the active, intercooled, flow-controlled and intercooled recuperative core should be able to appreciably reduce emissions and fuel consumption, and the program will build and test new components for these core engines.
However, as Korsia observed in Budapest, “Improving components alone cannot bridge the gap from existing engines to the ACARE targets.” The current programs, accordingly, will feed the much bigger Clean Sky effort.
Snecma’s deputy vice president research and technology, Isabelle Dubois, told the VITAL workshop that as well as speeding up the delivery of breakthrough technologies to mitigate the environmental impact of traffic growth, the Clean Sky joint technology initiative aims to increase the competitiveness of the European aerospace industry.
The program comprises six integrated technology demonstrators (ITDs), three of them aircraft: a smart fixed-wing aircraft able to adapt the shape of its wings; a green regional aircraft designed for low weight and low noise; and a green rotorcraft with quieter blades and other improvements, including diesel engine technology.
The other three are a sustainable green engine (SAGE), which will look at novel configurations such as open rotors and intercoolers; electrical and other systems for green operations; and eco-design, which covers the whole product lifecycle from raw materials to recycling. There will also be a simulator network, the technology evaluator, to quantify the combined environmental impact of the various technologies.
With a €1.6 billion budget, half from the European Commission and half from the participants, Clean Sky is scheduled to last seven years. The final stage will be flight tests in 2013-2014.
Snecma and Rolls-Royce are joint coordinators of the SAGE demonstrator, which comprises five engine types: geared and direct-drive open rotors, a large three-shaft turbofan, a geared turbofan and a turboshaft for helicopters. Airbus and Alenia are partners in SAGE, while Avio, ITP, MTU and Volvo are associates.