DLR and Lufthansa Technik produce study on aviation biofuels

Biofuels have the potential to improve the carbon footprint of the aviation industry and make the sector more environmentally friendly, according to a new study from the German Aerospace Center (DLR) and Lufthansa Technik.

The DLR and Lufthansa investigated the chemical and physical properties of “promising” biofuels. The European Union-funded High Biofuel Blends in Aviation (HBBA) study focused on blends, i.e. mixtures of conventional kerosene with biofuels.

The study analysed particularly promising biofuels, according to source, production process and approval status.

An airliner turbine can cost up to several million euro. 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 Institute of Combustion Technology had 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 three different fuels: pure biofuel, a blend consisting of 50% biofuel and 50% conventional fuel, 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.

According to the organisations, the experience was “impressive” not only from a scientific point of view: "The test engine – a CFM56, 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, said 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," added Köhler.

Improved carbon footprint with biofuel blends

"This large-scale test showed that the use of blends can improve the carbon footprint in the field of aviation without causing any problems in the engine," said Köhler. "Furthermore, with biofuels, we see the potential to reduce the emissions of pollutants in the future."

For this reason, the subject is increasingly attracting interest from airlines, aircraft manufacturers, airport operators and local residents.

In a statement, the organisations stated: “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.”