"Answering tomorrow's challenges": Never before has MTU Aero Engines had such good answers ready as today to tackle the challenges the aviation industry will be facing down the road. "We're conscious of our responsibility for sustainable, emissions-free flying. That's why we're already investing today in pioneering technologies for the aviation of tomorrow," explains MTU's COO Lars Wagner. At this year's Paris Air Show the company will present truly pioneering ideas and concepts: innovative evolutionary technologies for the next engine generation and also revolutionary technologies for the year 2050 and after.
"In the commercial segment, we're researching several evolutionary approaches that are already possible today thanks to sustainable e-fuels. At the same time, we're looking into alternative engine concepts ranging from hybrid-electric flight to fuel cells," Wagner continues. With MTU's contributions to the Geared Turbofan™ (GTF) engine, the company is impressively shaping developments in the industry of the present while preparing to shape the future like never before in the company's history: the second GTF generation still offers considerable potential. Once it has been further optimized, it will dramatically reduce emissions and is due to be airborne by the mid-2030s.
Profile of commercial aviation in 2050
However, MTU's experts are not satisfied to leave it at that; they are casting their gazes further into the future. Part of a small band of visionaries worldwide, they are already working with partners from industry and research on ideas for the commercial engines that could fly from 2050 onwards. Dr. Jörg Henne, Senior Vice President Engineering and Technology, explains: "MTU is working out revolutionary engine concepts to achieve the ambitious goals of Flight path 2050. These new engine solutions have to go beyond today's technology, with emissions-free flight the greater goal."
Resourceful MTU developers have come up with two approaches and are combining the tried-and-tested gas turbine engine with brand new technologies: in the composite cycle approach, the conventional high-pressure compressor system is to be complemented by a piston compressor and engine. "This will allow us to significantly increase thermal efficiency," says Dr. Stefan Weber, Senior Vice President Technology & Engineering Advanced Programs. The STIG cycle engine, meanwhile, integrates a steam power process into the gas turbine processes. This involves using a gas turbine with steam injection to feed the heat of the exhaust stream back into the process inside the engine. The wet combustion would substantially reduce both CO2 and NOx pollutant emissions. "We'll have to see which approach ultimately offers greater potential and is economically feasible," Weber says. If this turns out to be the STIG cycle engine, it will not work in the current aircraft architecture, thus calling for a new configuration.
Sustainable, renewable fuels
Work on these two MTU pilot concepts is being accompanied by other activities. "These measures alone won't be enough for us to reach the ambitious goals for 2050," says Weber. "They will get us a good part of the way there, but by no means will they let us achieve them completely. We need to close the remaining gap through the development of sustainable fuels." The idea is to shift away from consuming fossil fuels toward sustainable, renewable fuels. "We want to encourage their use," Weber says. Promising approaches for producing synthetic fuels are offered by solar energy and by electricity—provided it is generated sustainably. The latter technology is already available today. One of the major advantages of synthetic fuels is that they don't require any new infrastructure; they can simply be "dropped in" to existing kerosene-based infrastructure. To completely cut out NOx emissions as well, there's no getting away from fuel cells—meaning flying with hydrogen. MTU has this technology in its sights, too.
One topic has been gaining more and more public attention recently: electric flying. This is because purely battery-driven aircraft fly completely emissions-free—provided the electricity they use has been generated sustainably. "Emissions-free" does not include noise, as this simply cannot be fully avoided when it comes to flight. Realistically, however, from today's perspective there are large obstacles to overcome before we will see purely battery-powered passenger aircraft. Weber elaborates: "Electric propulsion systems and batteries reach performance levels today that permit their use in power gliders, sporting airplanes and other aircraft in that class." But at present, transferring this technology into aircraft in the Airbus A320 class is impossible, as the battery capacity falls far short of what's needed. "And we currently see no promising technological approaches opening up in the future."
What does seem technically feasible from today's perspective are turbo-electric or hybrid-electric systems that integrate the turbo machinery and generator into the aircraft fuselage. The current for the electric motors could be generated by a gas turbine; in turn, the electric motors would power distributed fans on the wing. Whether there is truly potential to be tapped with this approach remains to be seen. Success ultimately hinges on technical progress in the field of batteries and electric motors. MTU has its finger on the pulse here, too, and is involved in various studies and initiatives: for example, it is collaborating with partners to investigate hybrid-electric or all-electric power trains for air taxis or even 19-seater aircraft.
Gas turbine will continue
MTU's experts are certain about one thing: "As a concept, the gas turbine engine will continue to hold sway. It's fit for the future and holds potential for further optimization." Using sustainable drop-in fuels with the existing infrastructure would make it possible to quickly put a significant dent in pollution emissions. There are two conceivable applications for the gas turbine in aircraft: either as an improved, greener main engine or else as the basis for low-emissions hybrid systems, insofar as their introduction is proven to be beneficial overall.
MTU has positioned itself clearly: it is eyeing all possibilities for ensuring further progress in the skies. After all, as the experts know, the future of aviation begins today.