A new EU-funded initiative to develop radical concepts for ultra-efficient aero engines will focus on revolutionising the core of the powerplant, for deployment on future advanced tube-and-wing aircraft.

Work on the €3 million ($3.4 million) “Ultimate” (ultra-low-emission technology innovations for mid-century aircraft turbine engines) project began last year and will continue through to 2018, by which time participants envision that the concepts developed will have reached technology readiness level 2 (TRL 2).

Academics and engine manufacturers will then examine the ideas and select those deemed the most feasible for further development, with the aim of incorporating the radical technology into short-range and intercontinental advanced tube-and-wing aircraft from 2050.

“Ultimate is a low technology readiness project, so it is fully focused on paperwork. These are the first steps. The aim is, at the end of the paperwork, to look at the concepts and see whether to [proceed with any of them]. They will all be evaluated and we will also look at whether we could combine the different approaches to get even higher benefits,” says Stefan Donnerhack, engineer of advanced product design at Germany’s MTU Aero Engines – one of four engine manufacturers involved in the project.

Also involved are Rolls-Royce, Safran Aircraft Engines and GKN Aerospace. The four manufacturers will work alongside project co-ordinator Chalmers University of Technology, the UK’s Cranfield University, Aristotle University of Thessaloniki in Greece, France’s Institut Supérieur de l’Aéronautique et de l’Espace, Germany’s Bauhaus Luftfahrt research institute and French technology management company Arttic.

Ultimate ATW

Europe is seeking a 75% reduction in carbon dioxide emissions from aviation by 2050: a goal which must in part rely on radical technologies

Chalmers University of Technology

Under its Strategic Research and Innovation Agenda (SRIA 2050), the EU is seeking a 75% reduction in carbon dioxide emissions from aviation by 2050, relative to the year 2000, through the use of evolving technology and what it calls “radical technology shocks”. This must be achieved alongside a 90% reduction in nitrogen oxide (NOx) emissions and a 65% reduction in perceived noise.

According to the Ultimate project’s organisers, “technologies currently at TRL 3-5 cannot achieve this aim. It is estimated that around a 30% reduction must come from radical innovations now being at lower TRL. Existing tools, knowledge and models will be used to perform optimisation and evaluation against the SRIA targets to mature the technologies to TRL 2”.

Tomas Grönstedt, professor of turbomachinery at Chalmers University of Technology, believes the last 18% of the EU’s 75% target “will have to come from radical technology developed within our project”.

“We hope to time a powerplant that can achieve these targets and we hope that [Ultimate will provide] input to the industry to put in their technology roadmap so that it actually gets done,” Grönstedt says. “We will mature engine concepts that today only exist as ideas, by combining technologies in an unprecedented way. The kinds of radical solutions we will be exploring could completely change the layout and appearance of future engines.”

Today’s aircraft engines typically have an overall efficiency of about 40%, but this could potentially exceed 60% by combining radical design concepts which target the main sources of loss with ongoing improvements to conventional components.

Grönstedt characterises the three biggest sources of loss as being combustor irreversibility, core exhaust heat loss and excess kinetic energy in the bypass flow. With research already well under way on the latter, in the form of advanced geared and open rotor concepts, the Ultimate project will primarily focus on addressing the first two sources of loss.

“The main mission of the Ultimate project is [to develop] novel engine concepts,” says Donnerhack, noting that unlike changes made to the fan section – which require “close co-operation and studies together with the airframer” because they often result in changes to the size and weight of the engine – alterations to the core are less likely to face this hurdle.

“We will look at engines with an entry-into-service date of 2040-plus and, obviously, related aircraft will evolve towards 2040 anyway. But these are evolutionary changes, not radical changes – this is one constraint of the Ultimate project and distinguishes it from other related studies,” says Donnerhack. “The approach is similar to what the industry is doing with re-engining existing aircraft, but Ultimate goes at least two steps beyond today’s turbomachinery modules.”

Grönstedt adds that by focusing on the core section of the engine, the technologies discovered “can be put in a large number of scenarios” that go beyond the advanced tube-and-wing configuration at the heart of the Ultimate project.

“There are many different solutions with embedded engines and distributed propulsion, and in all scenarios a very efficient core is useful,” says Grönstedt, pointing out that more radical aircraft designs, such as blended wing body configurations, “would all benefit from an advanced core”.

One of the core technologies that Ultimate will examine to reduce combustor component loss involves combining the benefits of piston engine technology with those of the modern gas turbine, to create a piston-topped composite engine cycle. Incorporating piston engine solutions could help to increase pressure during the combustion process, boosting the engine’s efficiency.

“When you look back to history and 50-plus years of development, we believe a state-of-the-art combination of a turbo-piston engine could [improve] fuel efficiency by 15-18%, relative to current state-of-the-art engines,” says Donnerhack.

Ultimate’s second key area of focus – reducing core exhaust heat loss – involves the use of intercooling and recuperation systems aimed at “exploiting energy and shifting it to other places in the engine where it is useful”, explains Donnerhack.

“[A] large source of loss comes from the fact that the exhaust air from the engine is still 500-700 degrees hotter than ambient. If this wasted heat can be recycled then major improvements can be expected,” says Grönstedt.

On the intercooling side, researchers will look at the potential to harvest rejected heat through the use of a secondary fluid system. The recuperation studies will examine compact heat exchange concepts and alternative staged heat recovery methods. Researchers will study new installations in the engine core and propose “a wider range of tube geometries” for assessment. The project’s organisers say that recuperation technology for intercooled engines research will also explore the noise-shielding capability of the heat exchanger. Donnerhack points out that MTU has previously carried out “extensive studies” on recuperation techniques.

Grönstedt is hopeful that by the end of the three-year project, the various research efforts will show signs of turning into something more tangible in the future.

“My view is that we should have this down-selected powerplant with a good chance of meeting the targets, we will have roadmaps for how to develop it and we can go on to the next stage,” he says. “We will boil it down to one or two concepts and find ways to go from an idea that’s radical to something that companies can see happening and want to invest in.”

Source: Flight International