MTU and Bauhaus Luftfahrt: Simulations and future propulsion concepts

What will tomorrow’s aircraft look like? Engineers from MTU Aero Engines and the aviation think tank Bauhaus Luftfahrt have been working hard in small online teams to come up with technology and design proposals. They have had full conceptual freedom to explore where their ideas might take them. Now, they have all gathered in the same conference room at the Ludwig Bölkow Campus in Taufkirchen near Munich and the first of nine concepts is being projected onto the wall.

Today is all about tomorrow’s propulsion concepts. The evolutionary development of the gas turbine will not be enough to meet the Paris Agreement’s ambitious target of limiting global warming to, ideally, an increase of 1.5 degrees Celsius compared to preindustrial levels. What is needed are revolutionary propulsion concepts. One such concept is the water-enhanced turbofan, or WET for short. This is expected to mark a massive reduction in all factors that have a negative impact on the climate: CO₂, nitrogen oxides and contrails. Compared to today’s aircraft engines, the gas-turbine-based WET technology would also be significantly more efficient because it harnesses residual heat from the engine’s exhaust gas stream.

But what would this kind of turbofan have to look like? And how would it be integrated into an aircraft? Should it be installed on the underside of the wings like a conventional engine? Or will it have to be integrated very differently and thus change the design of the entire aircraft? “The WET concept is a revolutionary idea that is still in the early stages of development, which is precisely the right time to ask these questions,” says Fabian Donus, Innovation manager at MTU. “Our collaboration with Bauhaus Luftfahrt helps us find answers to these questions: the team there has the skill required to integrate our engine designs into the overall aircraft model. This is the only way to identify the optimum design.”

Programs that see what does not yet exist

Labs, measurement devices and test facilities are nowhere to be found at Bauhaus Luftfahrt in Taufkirchen near Munich. Instead, employees at the Ludwig Bölkow Campus work in offices, doing most of their research on a PC. “We use programs that let us simulate things like aerodynamic behavior and determine key design parameters such as resistance, weight and efficiency—long before an aircraft is built. This is also how we calculate the WET concept’s energy requirements, fuel consumption and climate impact,” explains Dr. Jochen Kaiser, Head of Visionary Aircraft Concepts at Bauhaus Luftfahrt. “Changing the design of an aircraft and its engine can either enhance or worsen these KPIs. That’s why it’s so important that early on in development we simulate whether a concept has what it takes to save energy and reduce climate impact.”

The Bauhaus engineers specialize in this kind of simulation, having spent many years building up the necessary skills and methods for creating a conceptual aircraft design. They make it possible to evaluate how new propulsion concepts will affect the aircraft’s overall design. Ultimately, this also provides early insights into the performance and improved environmental impact of future commercial aircraft.

The experts at Bauhaus have calculated the performance data for all of the engine-aircraft configurations being considered for WET. “The appeal of the simulations is that we can try out anything we like. Since it’s all virtual, we can visualize and evaluate the various options. That’s a massive help when making a decision,” says Dr. Sascha Kaiser, Lead Water-Enhanced Turbofan at MTU. The winning design features engine nacelles, which—as is customary—can be installed on the underside of the wings. This solution offers several advantages: it requires only slight modifications to the aircraft, it means the engine is easily accessible and it is compatible with existing airport infrastructure.

Support from the multidisciplinary think tank

MTU and Bauhaus Luftfahrt’s collaboration on the WET concept is just one of their joint projects. “The think tank is a prime example of multidisciplinary collaboration,” says Dr. Arne Weckend, Technology Collaboration Representative at MTU. “Founded by a group of different players in the industry—manufacturers of engines, aircraft and aircraft systems as well as the state of Bavaria—the think tank works closely with airport operators and fuel developers. This means that the team there has an impressively wide range of interdisciplinary contacts and comprehensive skills for evaluating the new aviation and propulsion concepts this network generates.”

Bauhaus expertise has also helped shape MTU’s Claire technology agenda: Bauhaus experts were at the table back in 2007, when the first version of Claire—which stands for Clean Air Engine—was drafted. In addition to reducing noise levels and exhaust emissions that are harmful to people’s health, the focus was on the fuel consumption of the various engine concepts. Bauhaus was also involved in this year’s update—emissions-free flight is now a Claire goal.

Simulations for emissions-free aviation

But will this actually happen? Together, the partners have come up with a number of ways to dramatically reduce aviation’s climate impact in the future, and developing the WET technology is one of them. However, the first product isn’t expected to be available until around 2035. First, its potential will have to be proved and its feasibility verified.

In the short term, extensive use of sustainable aviation fuels (SAF) will help reduce emissions; these green fuels can already be added to standard kerosene. SAF can also be used to power the water-enhanced turbofan. In the near future, all aircraft are to run on 100 percent SAF—double the maximum proportion that is currently approved. “The simulations produced at Bauhaus Luftfahrt show that using 100 percent SAF would very likely prove relatively straightforward, requiring only minimal modifications to engines and aircraft,” Donus explains. “What’s more, existing airport infrastructure could probably remain in place.”

In the long term, another concept will also be launched: the flying fuel cell, or FFC for short. Developed by MTU, the FFC converts liquid hydrogen into electricity, which a highly efficient electric motor then uses to drive the propellor. This has the benefit of emitting zero CO₂, nitrogen oxides or soot particles. Since its only emission is water, the FFC is virtually emissions-free. Using hydrogen as a fuel, however, calls for new aircraft designs; hydrogen tanks are much larger than kerosene tanks and must have additional insulation. In commercial aviation, minimizing the volume of hydrogen on board means it must be used in its liquid form—at minus 253 degrees Celsius. In addition to working on a variety of design proposals, the Bauhaus team is currently evaluating how the production, transport and distribution of hydrogen affects the environment and the cost.

“Each approach has its pros and cons and will have to be judged on its own merits,” Kaiser says. “Our simulations ought to help the decision-making process by revealing the extent to which the various technologies can reduce emissions in aviation and in what timeframe.” Dryly, he adds that not even Bauhaus Luftfahrt can predict that on the spot. “Our goal is to provide the aviation industry with realistic assessments of its technology options for the coming decades. This will indicate ways of making emissions-free flight a reality.”