MTU Aero Engines is highlighting at its Dubai exhibit a pair of new propulsion concepts it views as strong prospects for decarbonizing air transportation starting in the 2030s. The German manufacturer is now accelerating engineering collaborations with multiple partners to advance both its Water-Enhanced Turbofan (WET) and Flying Fuel Cell (FFC) innovations.
The FFC will convert hydrogen into electricity to support future powertrains that MTU believes could advance the industry beyond the range and payload limitations of battery-electric aircraft. According to innovative propulsion director Fabian Donus, initial applications of the fuel cell technology to be ready for entry into service around 2035 will center on aircraft carrying up to 100 passengers on flights of up to 1,000 nm. Since the FFC would emit only water, its developers expect the innovation to reduce climate impact by as much as 95 percent.
MTU’s engineering team now has begun tailoring the architecture for the FFC, taking into account the need to optimize for weight and drag, factors that automotive applications have not had to address. They conducted some of the work through a partnership with Germany’s DLR Aerospace Research Center to use a 19-seat Dornier Do228 twin turboprop commuter aircraft as a testbed.
The company expects the technology demonstrator to be ready for flight testing around the middle of this decade, with an electric motor now being developed by MTU subsidiary eMoSys. The motor will integrate with fuel cell stacks in which hydrogen and oxygen react to form water that releases electrical energy.
Aimed at delivering new propulsion options for possible future narrowbody airliners by the mid-2030s, MTU’s WET gas turbine concept is part of the Sustainable Water-Injecting Turbofan Comprising Hybrid-Electrics (SWITCH) project, which has received backing from the European Union’s Clean Aviation initiative. The plan involves combining the WET technology with hybrid electric propulsion in Pratt & Whitney’s Geared Turbofan (GTF) engine.
Airbus is closely involved with the work, for which Collins Aerospace contributes megawatt-class electric motor generators and power electronics, high-voltage DC distribution and protection, thermal management components, and nacelles. GKN Aerospace provides access to its hot test rig in Sweden, and the group’s facility in the Netherlands is developing high-voltage electrical wiring.
The big idea behind WET is to reduce the output of harmful emissions while achieving significantly improved energy efficiency. According to Donus, about 45 percent of energy from current turbofans doesn't get used for propulsion. "So we want to recuperate this before it leaves the engine,” he explained. The process involves capturing heat energy with a heat exchanger vaporizer to produce steam that can be injected into the combustion chamber to provide more energy in a constantly repeated cycle. The water needed for the process gets extracted from the exhaust gas using a condenser and then separated.
Along with cutting carbon dioxide emissions by lowering fuel consumption, MTU aims to reduce nitrogen oxide (NOx) emissions by as much as 80 to 90 percent. The company says it will achieve that objective through the steam injection process by reducing the temperature peaks that produce NOx. The ongoing SWITCH work will seek to establish how such architecture could integrate into new airframes. The partners anticipate a fuel burn saving of between 5 and 10 percent compared with current GTF engines, and in the longer term, by around 2050, the technology could apply to the largest widebody airliners. Phase 1 of SWITCH should see ground rigs ready for testing by around 2025 or 2026, with Phase 2 due to deliver a demonstrator unit by the end of this decade.
MTU’s multimedia exhibit also features the EJ200 turbofan it produces for the Eurofighter Typhoon combat aircraft and aspects of its maintenance, repair, and overhaul services.