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 (Deutsches Zentrum für Luft- und Raumfahrt – 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. The European Union-funded High Biofuel Blends in Aviation (HBBA) study focused on blends (that is, mixtures of conventional kerosene with biofuels). The study analyzed particularly promising biofuels, according to source, production process and approval status.
An aircraft turbine can cost up to several million euros and 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 laboratory tests and implementation in an aircraft represents a huge challenge for researchers.
Scientists at the DLR Institute of Combustion Technology now can investigate biofuels on a special test rig at Lufthansa Technik in Hamburg, where an aero turbine engine is available for research purposes.
“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,” said DLR researcher Markus Köhler.
“A significant challenge here is stability of the probes under these extreme conditions so that they do not simply snap or bend. 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.”
Scientists have examined three different fuels: pure biofuel; a blend of 50/50 biofuel and conventional fuel; and conventional kerosene as a reference.
“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,” stated 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.
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.
June 14, 2017