Germany's Engine 3E (E3E) programme was launched to ensure that the country's aeroengine companies, BMW Rolls-Royce (now R-R GmbH) and MTU, are prepared for the demands that will be made of future powerplant designs - namely for significantly reduced fuel consumption, noise and emissions.
The overall aim of E3E is to achieve by 2010 a 20% reduction in fuel consumption compared with a typical 5:1 bypass-ratio turbofan, plus a 10dB reduction in noise levels and an 85%cut in NOx emissions compared with current International Civil Aviation Organisation (ICAO) standards. Lessening the environmental impact of jet engines is seen as vital if annual air traffic growth of around 5% - a doubling every 15 years - is to be sustained.
"This traffic explosion calls for a concerted effort to improve aviation's environmental compatibility," says MTU. "Among an aircraft's systems, it is the engine that holds the greatest promise of environmental and economic improvements. These essentially reside in novel propulsion concepts."
The problem is that improving propulsive efficiency by increasing bypass ratio demands greater thermal efficiency in the engine core, which must be achieved by increasing combustor exit temperatures and overall pressure ratios. Unfortunately, the latter tends to result in an increase in NOx emissions.
BMW R-R and MTU disagree fundamentally on the best way to tackle the problem, however. MTU toes the Pratt &Whitney line that a gearbox between the fan and low-pressure turbine is required, to optimise their respective rotational speeds. Insertion of a gearbox allows the low-pressure turbine (LPT) and compressor (LPC) to operate at higher rotational speeds and therefore to be made smaller and lighter. BMW R-R follows the Rolls-Royce line that a geared fan introduces unnecessary complexity into the engine and is not a practical proposition for airline operations.
Phase one of the 50%-government funded E3E project began in 1994 and comes to an end this year. BMW R-R focused primarily on combustor technology, while MTU concentrated on LPT work. Phase two, beginning this year, was to have culminated in the companies jointly building and testing an engine core, but this now seems unlikely. The two companies are reluctant to share their technology, given BMW R-R's ties with its UK parent and MTU's partnership with Pratt & Whitney. This means that many advances achieved as part of the E3E work will end up being incorporated in competing R-R and P&W products.
More than half of MTU's phase one work concerns high-speed LPT technology applicable to a geared-fan engine. "This was the clear focus for us in phase one," says technology co-ordination engineer Roland Lederer. Some of this work has been applied to P&W's PW6000, under development for the Airbus A318, although this is not a geared-fan engine. One result is a 20% reduction in LPT blade count, which reduces the manufacturing and maintenance costs that are "somewhat dominant" in the PW6000 market.
Another focus was on advanced materials such as titanium aluminide, used to make LPT blades withstand much higher temperatures than would be encountered in conventional engines, and the development of brush seals to reduce leakage flow and boost efficiency.
In combustor technology, MTU has concentrated on advancing conventional single annular designs to reduce NOx. Lederer says the company has achieved a 30% NOx margin against ICAO standards without use of the staged combustor favoured by BMW R-R.
The third major part of MTU's phase one work centred on high-pressure compressor technology - an area in which the company is keen to develop its expertise. MTU is responsible for the HPC for the Eurojet EJ200 powerplant in the Eurofighter. Lederer says there are common design processes involved in the development of high-speed turbines and compressors. These involve applying three-dimensional aerodynamic design techniques to produce blades capable of accommodating higher loads and circumferential speeds. "It's our clear intention to have work on the compressor side in future engines," says Lederer.
MTU has already started phase two of E3E, with work under way on three of six planned projects. These focus primarily on compressor development and should be completed in four years. Two HPC designs will be developed - the six-stage HPC12 for use in engines for short-haul aircraft and the nine-stage HPC22 aimed at long-range, big fan applications. MTU plans to conduct full core engine runs with the HPC12. Another phase two project will be the development of an LPT for use in future business and regional jet engines.
Development of software tools, for computer-aided design and computational fluid dynamics (CFD), is also a focus of phase two. "The goal is to make our tools faster, to allow a 30-month engine development time," says Lederer. This work is being performed in co-operation with BMW R-R and Germany's DLR research organisation.
During the first phase of E3E, BMW R-R concentrated on development of a staged combustor, HPT cooling-system seals and hybrid composite unison rings for use with blade-integrated disks. Some of this technology has been incorporated in the core of its BR715.
Phase one also included tests of a potential new high-temperature HPT material known as 720Li and CFD work on a new bypass and core exhaust-flow mixer designed to reduce noise. The company believes that enabling the HPT to operate at higher temperatures will be crucial in achieving significant improvements in efficiency and reduced noise levels in future engines. Another E3E work package examined "total engine control"in partnership with German control systems specialist BGT.
New engine core
The first phase of BMW R-R's E3E was completed in October 1999. The planned second phase, which remains subject to government funding approval, will focus on development of an all-new engine core designed to operate at higher temperatures than today's engines. This will include development of an advanced combustor, and a two-stage HPT incorporating the cooling system technology tested in phase one. It will also have 3D-aerodynamic compressor blades. The aim is to achieve a pressure ratio of 15 using seven stages.
"We hope to run the first complete core with all the new features in 2004," says head of concepts and technologies Dr Helmut Richter. "We will try to have an engine concept that really exploits the capabilities of the components. The objective is to have noise margins [against Stage 3] for the total engine which are in the area of 25dB," he says. "Any future two-shaft engine we are involved in as a member of the R-R family will feature this technology." Richter says the core technology could be incorporated in an all-new two-shaft engine by 2006-7. BMW R-R eventually hopes to launch a third phase of E3E which would involve testing a complete engine incorporating all the technologies being developed in the first two phases.
Looking further ahead, MTU plans to develop a geared-fan "European low-emission recuperated engine"(EULER) with Snecma, Volvo and Fiat, as part of the European Union's Fifth Framework research programme. Lederer says this technology could reduce fuel consumption and emissions by 10-15%.
The principle involves feeding air from the LPC through a heat exchanger in the bypass flow, where it is cooled, and then fed into the HPC. Compressed air leaving the HPC is then passed through another heat exchanger in the engine nozzle, drawing heat energy from the exhaust gases, and back to the combustor.
As well as boosting efficiency and reducing noise, Lederer says the concept promises a 10-15% cut in engine weight. Offsetting these benefits to a degree is the increase in complexity that results. According to Lederer, a EULER-type engine could be tested in around four years' time, but would be unlikely to enter service before 2015.
Source: Flight International
