MTU Aero Engines: Cleaner and Quieter Engines

At MTU Aero Engines, assuming responsibility – for products and services, employees, customers, partners, and not least for the environment – is a key priority. The biggest contribution of Germany’s leading engine manufacturer toward the protection of the environment comes from the eco-efficient products it makes using energy-efficient processes. “Product responsibility for us is the motivation that drives all of our business efforts,” emphasizes MTU Chief Executive Officer Reiner Winkler. “Eco-efficient and safe products are key to our long-term economic viability.”

The best case in point is the tremendously successful geared turbofan (GTF) engine: With this propulsion system, which goes by the catchy name of PurePower® PW1000G, Pratt & Whitney and MTU are building the propulsion system of the future. The new technology is a textbook example of how to meet the challenge of making engines even more fuel-efficient, cleaner, and quieter: The GTF immediately reduces fuel consumption and CO2 emissions by 15 percent each and almost cuts perceived noise levels in half. On top of this, it is expected that even more improvements can be achieved, bringing down fuel burn and CO2 emissions by 40 percent. These advances are made possible by optimizations of this engine, work on which is already underway. The market was quickly convinced of the benefits afforded by the GTF: Five aircraft manufacturers around the world have chosen this new propulsion system for their aircraft, and about 60 airlines, too, have selected the engine, the total order book standing at almost 7,000 copies.

What sets the new GTF propulsion system apart is that it features a reduction gearbox between the fan and low-pressure turbine. The two are connected by a shaft, and the turbine drives the fan. The gearbox allows the fan with its large diameter to rotate more slowly, and the turbine to rotate much faster. This lets the individual components achieve their respective optimum speed, greatly boosting the geared turbofan’s efficiency. The result is a significant reduction in fuel consumption, emissions of CO2, and noise; moreover, the propulsion system is much lighter, as it has fewer compressor and turbine stages than today’s engines. MTU contributes the high-speed, low-pressure turbine – a key GTF component – and, in collaboration with Pratt & Whitney, is building an innovative high-pressure compressor.

Today already, the GTF version to power the Airbus A320neo is playing a special role in the family of geared turbofans. The engine boasts two advanced technological developments: In this program, MTU is using a new additive production process and a new material for the first time. The high-speed, low-pressure turbine for the PW1100G-JM is the first production turbine ever to include an attachment part made by the 3-D printing method. New additive manufacturing processes greatly benefit the environment, since components can be produced with only small amounts of material and require few tools. From an economic perspective, too, they score high, since the technology opens the door to entirely new, more complex designs; appreciably cuts development, production, and lead times; and brings down production costs overall. MTU wants to take full advantage of the benefits and is pressing on with additive manufacturing in numerous technology projects and programs, giving its development top priority.

The second innovation incorporated in the GTF for the A320neo is a new material made by MTU: The rearmost rotor stage of the high-speed, low-pressure turbine is made up of tailor-made titanium aluminide blades. TiAl is a new intermetallic high-temperature material for highly loaded engine components in a class all by itself. It was developed by MTU and partners within the record time of a mere seven years. Its advantages: TiAl turbine blades are only half the weight of comparable nickel-alloy blades but boast the same reliability and durability. In this field, too, MTU is already working to push research forward and is busy developing an enhanced TiAl alloy. The aim is to make more turbine stages from the new material. Again, the innovation is good news for the environment – for TiAl allows engines to be built that use fewer resources, burn less fuel, and are cleaner and quieter than today’s models. “I’m sure that this material will help further bring down the weight of engines appreciably,” says MTU Chief Operating Officer Dr. Rainer Martens.

Eco-efficiency is the driving force of MTU’s production strategy. In its Clean Air Engine (Claire) technology roadmap, MTU has set out how it wants to go about implementing this strategy. Here, the engine experts combine the latest key technologies into a commercial propulsion system that, by the year 2050, will burn 40 percent less fuel, will reduce CO2 emissions by the same amount, and will cut noise levels by 65 percent. Plans are to achieve the CO2 and noise level targets defined by the European aviation industry and research community in the Strategic Research and Innovation Agenda in three stages.

The staged goals of Claire are 15 percent, 25 percent, and 40 percent less CO2. In the first stage, the geared turbofan engine alone already provides a reduction in fuel consumption – and hence CO2 emissions – by up to 15 percent; noise levels will almost be cut in half. Concept studies conducted as part of the second stage of Claire indicate that the GTF configuration lends itself as a platform for further development and improvement. For example, it is quite conceivable that the bypass ratio can be further increased by the year 2030 – from 12:1 (geared turbofan) to up to 20:1. Moreover, the thermal efficiency of the core engine can be enhanced by higher pressure ratios and temperatures. The aim is to increase the overall pressure ratio from currently almost 50:1 to 70:1. In the third and last stage of Claire, major changes are envisaged that may well go beyond today’s gas turbine technology.

Jointly with universities and other research establishments, MTU is conducting studies for this phase. Among the options under review is the use of highly efficient heat engines with extremely high pressures based on recuperative technologies to recover energy from the exhaust gas. Other conceivable concepts are looking at propeller noise shielding by the aircraft or fans distributed around the fuselage.
One thing is for certain already: For MTU, helping shape and push forward advances in aviation is – and will remain – a tradition to which the company is firmly committed.