Biofuels in Aviation

In a large-scale test, DLR researchers investigated the use of biofuels as well as blends of biofuels and kerosene in a real engine.

Biofuels have the potential to make air transport more climate-friendly and reduce dependency on fossil raw materials, since they are produced using renewable raw materials, such as oil plants, grain, algae and wood. Researchers at the German Aerospace Center (DLR) together with Lufthansa Technik and the Bundeswehr Research Institute for Materials, Fuels and Lubricants, investigated the chemical and physical properties of particularly promising biofuels.

An airliner turbine can cost up to several million Euros. Should it be operated using non-certified fuel for research purposes, for example, it may not be reinstalled in an aircraft. This means that bridging the gap between tests on a laboratory scale to actual implementation in an aircraft represents a huge challenge for researchers. For the first time, scientists at the DLR now have the opportunity to investigate biofuels on a special test rig at Lufthansa Technik in Hamburg, where a dismounted aero-engine is available especially for research purposes. Using this engine, the scientists examined and compared 3 different fuels: pure biofuel, a blend, as well as conventional kerosene as a reference.

Over a period of several days, a four-person DLR team first set up the measuring infrastructure required for the tests and then carried out the measurements. And the experience was impressive not only from a scientific point of view: “The test engine used in Airbus and Boeing medium-haul aircraft, for example – is suspended from the ceiling in a hangar. The exhaust gas stream enters a large tunnel behind the engine, where we installed our measuring probes to take samples. A significant challenge here is stability of the probes under these extreme conditions so that they do not simply snap or bend”, says DLR researcher Markus Köhler describing the procedure. “The laboratory analyses already showed that biofuels are well suited for use in aero-engines. Testing this under real-life test conditions, however, takes on an entirely different dimension,” continues Köhler.

The certification of a completely new fuel is an extremely elaborate and lengthy process. Blends of biofuels and conventional kerosene represent an important intermediate stage. Some of their properties correspond to those of normal kerosene, which means that not all parameters required for the combustion process have to be completely re-examined. They are also an important step toward so-called designer fuels. Such fuels are composed in such a way that their properties are as optimal as possible in terms of environmental friendliness and technical characteristics. Research in this field is a major focus for the DLR Institute of Combustion Technology.

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