Renewable fuels with excellent environmental profile

Scientists at RWTH Aachen University, the Max Planck Institute for Chemical Energy Conversion, and ETH Zurich have developed synthetic fuels that show an excellent environmental profile in detailed life cycle assessment and can be used directly in existing combustion engines.

One of the major challenges in the fight against climate change is to reduce greenhouse gases from transportation. Politicians, industry, and scientists are discussing the use of zero-emission, synthetic fuels for existing combustion engines. One advantage of so-called synfuels is that they can be produced from renewable resources such as green electricity, water, biomass, and carbon dioxide (CO₂). If the CO₂ is removed from the earth's atmosphere with the help of renewable electricity, synfuels close the carbon cycle completely.

Established production processes in existing infrastructure
Scientists from RWTH Aachen University, the Max Planck Institute for Chemical Energy Conversion, and ETH Zurich have now proposed a new fuel in an interdisciplinary study and tested it for use in today's combustion engines. The so-called hydroformylated Fischer-Tropsch fuel (HyFiT) can be produced by Fischer-Tropsch synthesis, an established process for the production of synthetic gasoline or hydrocarbons from carbon monoxide and hydrogen. The researchers have added a step to the process in order to convert part of the synthetically produced diesel into long-chain alcohols. The resulting alkane-alcohol mixture is optimized in such a way that it reduces the emission of particles and nitrogen oxides during combustion. Existing industrial infrastructure can be used for the production, storage, and distribution of HyFit fuels. At the same time, the synthesis gas can be obtained from biomass, CO2, waste, and renewable energies, so that the carbon cycle is completely closed, enabling CO₂-neutral production.

"Our results show that HyFiT fuels are a building block for the energy transition in heavy goods transport that the industry can implement directly. Their use in current engines would lead to tailpipe emissions that are far below the limits of the upcoming Euro 7 regulations for reducing emissions in road traffic," says André Bardow, head of the study and professor at the Institute of Energy and Process Engineering at ETH Zurich.

Test series with life cycle assessment tested using a van
In experimental tests with a van, the researchers proved that the HyFiT fuel emits significantly less particulate matter and nitrogen oxides compared to fossil diesel. The study results also show that the new fuel is compatible with current standards and components such as plastic seals in today's engines. Finally, the researchers compared 16 environmental impacts with those of a diesel vehicle and a fully battery-electric vehicle. This showed that the use of synthetic fuels has a beneficial effect on the environment even in comparison with electrically powered vehicles, especially over long distances.