Toward zero emissions
Climate impact of aircraft engines
Climate action plays an immensely important role in MTU’s product development. Our technology agenda guides the hard work we are doing to substantially reduce aircraft engines’ fuel consumption and climate impact in several stages. Our long-term goal is to develop new propulsion concepts to make aviation emissions-free in the future—an important step toward achieving the target set out in the Paris Agreement.
Climate change is one of the greatest global challenges of our time. There is broad consensus in society on limiting climate change, preferably to a temperature increase of 1.5 degrees Celsius (target adopted at the 2015 UN Climate Change Conference in Paris). For the aerospace industry, this calls for a drastic cut in global greenhouse gas emissions. But not only that. We also have to mitigate the overall impact these emissions have on the climate (CO2 and non-CO2 effects). MTU has made climate action a key focus of its sustainability strategy and pursues ambitious goals. Given that the greatest climate impact over an aircraft engine’s entire lifecycle occurs in flight operations, MTU’s primary focus here is on its products’ service life. We are actively pursuing decarbonization, i.e. the shift to a long-term carbon-free economy, and include our own business activities in this effort. → Learn more about this commitment and our ecoRoadmap under Environmental protection in production
Even though the aviation market slumped as a result of the global coronavirus pandemic, it will return to its growth trajectory in the medium term. According to forecasts, the active aircraft fleet is still set to double by 2036, so now is the time to act decisively and set the course for a successful transition to renewable energy in aviation. Our activities center around significantly reducing the impact that air transport has on the climate; our long-term goal is emissions-free flight. The only way we can do this is if the entire industry pulls together and policymakers implement the appropriate framework. For that reason, we are involved in numerous aviation initiatives and forge new cooperative ventures to work on promising concepts with others. In our view, this transformation can succeed only if society as a whole pulls together, with the research community, industry and policymakers all collaborating closely.
Our contribution to SDGs 9, 12 and 13
With our commitment to climate action in product development, not only do we support important strategies such as the Paris Agreement and EU Green Deal; we also contribute to the SDGs, in particular to SDG 13 on “Climate action” and SDG 9 on “Industry, innovation and infrastructure”, and also to SDG 12 on “Responsible consumption and production.” This enables us to fulfill our commitment to the UN Global Compact (UNGC), a unique sustainability initiative in which many companies and organizations around the world have joined forces to make globalization fairer and more environmentally friendly. With our measures described here, we are making progress toward UNGC Principles 7 to 9, which come under the category of Environment.
Climate action guides how we conduct our business
We are long-time advocates of environmentally compatible aviation, and sustainable product development is enshrined in our MTU Principles with a view to reducing the harmful impact on climate and health. We have also formulated corresponding guidelines in our global MTU Code of Conduct. In our revision of the MTU Code of Conduct in the reporting year, we placed a much clearer emphasis on climate action as the key maxim guiding how we conduct our business. We see our Technology roadmap toward emissions-free flight as an ambitious contribution to society’s key goals for sustainable development. These include the EU Green Deal aimed at making Europe climate-neutral by 2050 and the international community’s Paris Agreement. As a manufacturer of aircraft engines, we see it as our responsibility not only to support this path, but also to put forward solutions. We are already hard at work on our Green Deal for aviation with revolutionary propulsion concepts high on our agenda.
Aviation’s climate impact goes beyond CO2
The United Nations Intergovernmental Panel on Climate Change (IPCC) reports that the climate impact of air traffic is due mainly to CO2 emissions, but also to ozone production as a consequence of NOx (nitrogen oxide) emissions, and the formation of contrails and cirrus clouds. According to the International Energy Agency, global air traffic is responsible for some 2.7% of CO2 emissions around the world (data from 2015). Conducted in 2020, a new international study led by Manchester Metropolitan University in collaboration with the German Aerospace Center (DLR) evaluated all the emissions from aircraft engines that contribute to climate change using an advanced IPCC metric. The study included CO2, NOx, water vapor, soot, aerosol and sulfate aerosol particles, contrails and cirrus clouds in its calculations, finding that global aviation is responsible for 3.5 percent of human-induced climate change. It also shows that CO2 emissions are responsible for only one-third of aviation’s impact on the climate, with the other two-thirds due to non-CO2 effects. Contrails and cirrus clouds (clouds of ice crystals) also have an impact on the climate; they are generated under certain temperature and humidity conditions in the atmosphere triggered by particle and water emissions. Clever selection of flight routes and altitudes can greatly reduce or even avoid them. Contrails can also be reduced with the help of sustainable fuels, as these produce fewer particulate emissions due to a lower proportion of aromatics. New combustor concepts can significantly reduce nitrogen oxides.
We align our activities with the Paris Agreement
Efficiency is key to environmentally friendly air travel. Fuel consumption and CO2 emissions are directly proportional and a considerable factor in the impact aviation has on the climate. This is why improving fuel efficiency remains very important to us, as it reduces both resource consumption and the impact on the climate. Given our expertise in the development and manufacture of high-pressure compressors and low-pressure turbines, this is something we directly influence. But the efforts to date are no longer enough.
The goal set out in the Paris Agreement, to limit the temperature increase preferably to 1.5 degrees Celsius, requires all activities to be accelerated and stepped up. And instead of just focusing on CO2 emissions, a shift is required to include all emissions that impact the climate. That is why, in addition to reducing fuel consumption and thus engine CO2 emissions, MTU is increasingly focusing on reducing contrails and cloud formation and, alongside evolutionary development of gas turbine technology, is also researching new, revolutionary propulsion concepts that range all the way to emissions-free solutions. Our technology roadmap toward emissions-free flight charts a long-term course to achieve zero-emission aviation. It outlines key new propulsion technologies required to make this happen and notably includes sustainable fuels and hydrogen-powered fuel cells as a long-term propulsion concept.
Another important objective set out on our technology roadmap is to reduce the impact of noise and exhaust emissions on health. → More information about this under Health impact of aircraft engines
New roadmap featuring concepts for zero emissions
The aviation industry is characterized by long product cycles. As a rule, aircraft engines spend 30 years in service before they are decommissioned. Goals to produce more eco-efficient engines therefore have a long-term perspective and are established in memoranda of understanding by the aviation stakeholders (airlines, aviation industry, research, aviation authorities). One example is the Strategic Research and Innovation Agenda (SRIA) developed in 2012, which we have always used as our benchmark. However, as the goals set out in the Paris Agreement for reducing climate impact are far more ambitious, we are currently realigning our Clean Air Engine Agenda (Claire) as our next step. This in-house roadmap for the development of engine programs sets several climate targets for MTU itself through to 2050. By realigning it, our aim is to accelerate the development of new propulsion concepts and implement emissions-free concepts. Publication is due in 2021.
We have already achieved a great deal: The geared turbofan engine
The first generation of the geared turbofan engine family already powers 940 aircraft, helping reduce CO2 emissions by 4.2 million metric tons.
(Source: Pratt & Whitney, February 2021) The engine is a key driver of revenue in our portfolio.
With the first generation of the geared turbofan engine family, which we develop and manufacture together with our partner Pratt & Whitney, we have not only achieved but in fact exceeded our first climate target of a 15% reduction in CO2 emissions (16% for the PW1100G-JM that powers the A320neo, for example). By 2022, this engine family will have been successively introduced in various models for a total of five aircraft applications. It has become a major business success and measurably reduces the burden on the environment: this first generation has already enabled airlines to save more than four million metric tons of CO2 in flight. It also brings significant improvements in terms of NOX emissions, which are 50% lower than those of its predecessor.
The next stage in our roadmap: 25% less fuel by 2030
Following the promising launch of the new geared turbofan engine, we now want to reduce fuel consumption and CO2 emissions even further. To achieve this, we are taking an evolutionary approach based on the geared turbofan, which still offers huge potential for improvement. In the next generation, we want to develop its technology and turn it into an ultra-high bypass engine. Running the new engines on sustainable aviation fuels (SAFs) would even pave the way for carbon neutrality. Because SAFs also cause lower soot emissions, engines in turn have less of an impact on the climate, since a reduction in soot reduces the number of contrails and cirrus clouds. Our engineers are already busy working on preliminary designs and technologies for the new generation. Within the German government’s LuFo aeronautics research program and European technology initiatives such as Clean Sky 2, we are driving development to get these concepts ready for full-scale production, for example by preparing tests on new high-temperature materials. This technology development work could be completed by 2027.
Rethinking propulsion: Claire stage 3 engine architectures
As part of the third stage of our Claire agenda, we are working with industry partners as well as universities and research institutions on solutions for 2030 and beyond. This is when new propulsion concepts are set to come into use that open the door to emissions-free flight. To this end, we are pursuing two concepts.
Water-enhanced turbofan (WET engine)
The water-enhanced turbofan (WET engine) employs a heat exchanger to use the energy from the engine’s exhaust gas stream. It works by evaporating water in a heat exchanger and injecting the vapor into the combustor for the turbine to generate additional power. A condenser is employed to obtain the requisite water from the exhaust gas. “Wet” combustion of this kind massively reduces nitrogen oxide emissions. This concept also cuts fuel consumption and CO2 emissions by a large degree. In addition, it holds great potential for significantly limiting the climate impact caused by contrails because it enables emissions of water vapor to be reduced. We started initial trials in 2020 to condense water from the engine’s exhaust gas stream for application in a WET engine. If this concept proves to be viable, there will be a further challenge to solve together with the aircraft manufacturer: how to integrate the required condenser into the aircraft.
The major advantage of this technical solution is that the WET engine can be designed to fly all ranges. Since the majority of aviation’s climate impact is the result of medium- and long-haul flights, the WET Engine holds great potential to reduce this impact. If the engine ran on SAF, its would be carbon-neutral to operate and the significantly lower particulate emissions would also help reduce contrails. Another conceivable source of power is hydrogen, which would eliminate CO2 emissions and soot entirely.
Electric propulsion: From battery-electric and hybrid concepts to fuel cells
Battery-electric propulsion systems enable zero-emission aviation—provided the power is produced sustainably. Currently, however, they are not technically feasible for existing commercial passenger aircraft. Today’s battery concepts do not offer anywhere near the energy density of conventional kerosene. Batteries’ storage capacity is far too small to power commercial flights. But battery-electric flight is a viable option for carrying a small number of passengers over short distances.
One possible concept for longer distances would be hybrid propulsion systems combining electric motors, generators, gas turbines and batteries. These open up completely new possibilities in aircraft design and propulsion technology while still using kerosene or SAFs as high energy density fuels for greater range. Disadvantages of hybrid propulsion systems, however, are the significant weight they add and energy conversion losses. We are participating in this future propulsion concept through our stake in Silent Air Taxi, which will have a parallel hybrid-electric propulsion system.
One very promising propulsion concept is the hydrogen-powered fuel cell as an emerging technology for sustainable aviation. It emits nothing but water and water vapor, paving the way for climate-neutral flight. This concept uses hydrogen as its energy source and employs electric motors to drive the propulsors. Hydrogen has a very high energy density, so—in contrast to the electric battery—a fuel cell could conceivably also power long-distance flights. However, the fuel cells available today are not suitable for use in larger aircraft. That notwithstanding, due to the enormous potential the technology holds and encouraging approaches for automotive applications, we are pursuing this concept as a long-term solution and established a Flying Fuel Cell team in 2020 to explore the development of an electric propulsion system with fuel cells. We have also teamed up with DLR to collaborate on a flight demonstrator for electric propulsion systems (flying fuel cell demonstrator), which is based on a modified Dornier Do228 turboprop aircraft. We signed a joint declaration of intent for this project in the reporting period. The maiden flight is expected to take place at the middle of the decade, for which the engineers are replacing one of aircraft’s two engines with a 500-kilowatt electric motor powered by electricity from a fuel cell. As many as 80 experts are set to work on this pioneering project.
To enable passenger aircraft powered by fuel cells to fly, however, different technologies are required—first and foremost, the fueling system. In gas form, hydrogen occupies a huge volume, even when stored in pressure tanks; liquid hydrogen cooled to minus 253 degrees Celsius is three to four times as voluminous as kerosene. For distances of up to about 3,500 nautical miles (just under 6,500 kilometers), in our view it still makes sense to accommodate the hydrogen tank, with modifications, in the current aircraft configuration. For longer routes, other solutions such as our WET engine are better.
Essential for green aviation: Sustainable fuels
Our position is clear: aviation must move away from the use of fossil fuels and tap far deeper into renewable energy sources. Sustainable fuels have the potential to neutralize CO2 emissions generated by aviation, which makes them an indispensable part of efforts to achieve the target set out in the Paris Agreement. MTU is strongly committed to the adoption of alternative aviation fuels. For instance, through our involvement in the Bauhaus Luftfahrt think tank and the Aviation Initiative for Renewable Energy in Germany (aireg), an association we set up together with airlines, manufacturers and research institutions.
Sustainable aviation fuels (SAFs) can already be used in today’s infrastructure as an admixture of at least 50 percent. The new fuels can be “dropped in” to existing infrastructure, which means there is no need to modify the engine or aircraft. Currently, however, SAFs are used only in minimal quantities. Basically there are two different production methods: biomass-based and synthetic fuels. It is essential that biomass-based processes do not stand in the way of food production. One way to ensure this is by converting waste and residual materials into kerosene. Compared to the methods used today, advanced processes such as biomass-to-liquid can achieve even greater sustainability because very few CO2 emissions are generated in the production of the fuels. In addition, a diverse range of raw materials can be used, which helps avoid changes in land use.
Unlike biomass-based SAFs, the scalability of synthetic fuels is virtually unlimited. These synfuels, as they are known, are produced using renewable electricity or sunlight, for which the power-to-liquid (PtL) process is particularly suitable. Although this technology is known and approved, there are still no large-scale production plants. As a result, prices are still very high; currently many times higher than for standard kerosene. A ramp-up to industrial scale, however, is expected to significantly reduce the cost. To produce this PtL fuel in large volumes, sufficient quantities of renewable energy must be available. Stepping up efforts to source even more energy from renewables is therefore also central to the use of SAF.
In addition to SAF, hydrogen can be burned directly as an alternative source of power for gas turbines. To enable this, the modifications to the geared turbofan would be relatively easy to make. When it comes to the aircraft and infrastructure, more extensive adjustments are likely to be required, as the entire fueling system will have to be changed or the fuel systems at airports will have to be adapted. As is the case with SAF, sufficient quantities of renewable energy are required to provide green hydrogen.
Zero-emission aviation: a white paper by Germany’s aviation research community (in German)