Biofuels and blends: renewable fuels for greener air travel

The goal of the international air transport industry is ambitious: Global air traffic should achieve carbon-neutral growth by 2020 and reduce net carbon emissions by 50% from 2005 to 2050. In addition to technological advancements and emission reductions, the use of renewable fuels, otherwise referred to as biofuels and blends, is pivotal here. The Japanese airline All Nippon Airways (ANA) is taking a bold step forward in this respect, with the wish to have the first commercial airplane fly on algae-based biokerosene by the 2020 Olympic Games in Tokyo.
Flying with algae? “The fact that the algae oil can be used as a source of biokerosene is beyond dispute – it works,” says Andreas Müller, who is responsible for coordinating the activities of the Institute of Bio- and Geosciences at Forschungszentrum Jülich (Jülich Research Center – FZJ). The FZJ has already investigated the production of algae and its conversion into biokerosene in its project known as “Aufwind”. “Test flights have been conducted with a blend which uses algae oil as a so-called ‘drop-in’ fuel,” he explains. The fuel has the same level of quality as fossil fuel-based kerosene.

Biokerosene made out of algae

Algae-based biokerosene cannot yet power entire fleets of aircraft. “At present, it’s just not possible in terms of logistics,” says Müller, who also works for the Berlin-headquartered Aviation Initiative for Renewable Energy (Aireg). A sustained supply of raw materials could not be guaranteed until now. If an airline is, however, able to provide the required quantity and quality of the alternative aviation fuel at all its locations – in other words, in every country and every region – it would be able to fly 100% “clean”. Technically, it’s not a problem to produce biokerosene from algae. “The core issue is really the cost,” says Müller.

Besides testing algae, experiments are also being conducted on other plants such as Jatropha to produce liquid fuels from their oils. Waste fats (i.e. waste materials) are also sources of energy and therefore offer great potential. “Many different technological developments exist, but in the end, they are all required in large quantities,” adds Müller. In most cases, they often fail because there’s currently not enough available. He sees the trend in combining different approaches. CO2-neutral synthetic fuels could thus play a central role in sustainable flying. These can be produced not only using biomass, but also with CO2-neutral electricity. Scientists from the Institute for Solar Research at the German Aerospace Center (DLR) want to use the “Synlight” project to develop production processes for solar-powered fuels, which also includes fuel for airplanes. The goal is to produce hydrogen by breaking down water into its different components. Hydrogen is regarded as the environmentally friendly fuel of the future, since it does not emit CO2 during combustion.

Large-scale test: Researchers from the
German Aerospace Center (DLR) tested the use
of biofuels and blends in a real engine
over a period of several days.
The DLR also confirms that biofuels have the potential to make flying more climate-friendly. DLR combustion researchers conducted a multi-day trial and tested the use of biofuels and mixtures of biofuels and kerosene (blends) in a real engine – the CFM56, which is used, among others, by Airbus and Boeing in their medium-haul aircraft. “This large-scale test shows that the use of blends helps to improve the carbon footprint of air traffic without causing any engine problems,” reports DLR scientist Dr. Markus Köhler.

Text by Nicole de Jong
Photos: Forschungszentrum Jülich (Article picture), DLR (CC-BY 3.0)