Schwerpunkte

Synthetic fuels

reFuels are suitable for broad use

15. Juli 2021, 08:34 Uhr   |  Irina Hübner

reFuels are suitable for broad use
© Markus Breig und Amadeus Bramsiepe, KIT

KIT produces reFuels itself. In the first step, various fuel mixtures of regeneratively synthesized fuel components (reFuels) and fossil fuels were investigated.

If reFuels are blended and prepared in such a way that they meet existing fuel standards, they can be used for all internal combustion engine applications. This is the result of tests in the »refuels – Rethinking Fuels« project at the Karlsruhe Institute of Technology (KIT).

reFuels are renewable fuels that can be produced via different routes. Compared to pure fossil fuels, reFuels fuel blends enable at least a 25 percent reduction in CO2. In addition, they offer slight advantages in pollutant emissions.

»Liquid fuels will be required in the mobility mix for some time to come, for example in long-haul heavy-duty transport, shipping and aviation, but also in the existing fleet of passenger cars. Here, synthetic fuels can offer a complementary solution option for the 'defossilization' of transport,« explains Dr. Uwe Wagner from the KIT Institute for Piston Machinery (IFKM).

»For this, they must be able to be produced sustainably and be available as quickly as possible,« adds Professor Nicolaus Dahmen, who is responsible for providing the fuels in the reFuels project. For all types of fuels commonly used today, there are established and new processes that supply the respective fuel. »The reFuels fuel blends currently being tested already enable at least a 25 percent reduction in CO2 compared to pure fossil fuels,« says Dahmen. In the reFuels project, this could be demonstrated for some examples for which KIT operates technologies or - as in the case of Hydrotreated Vegetable Oil (HVO) - has found another source for the fuels.

Practical tests show positive results

»The reFuels fuel blends we have investigated so far comply with existing fuel standards for gasoline and diesel fuels. In application tests in passenger cars in the existing fleet, we were unable to identify any detrimental properties with reFuels. In individual cases, there were even slight advantages in terms of pollutant emissions - for both diesel and gasoline vehicles,« says Wagner, summarizing the results of RDE (Real Driving Emissions) tests with commercially available R33 and G40 synthesized at KIT to date.

He and his team at IFKM investigated how reFuels behave in real driving conditions during RDE drives in Karlsruhe and the surrounding area. These drives took place on route sections in the city, on rural roads, and on the highway that comply with current legal requirements for the certification of new vehicles.

For the KIT test drives, four different passenger cars were equipped with a mobile emission measurement device (Portable Emission Measurement System, PEMS).

This device, which is also used in the European research project MetroPEMS, can measure nitrogen oxide, particulate, and CO2 emissions while driving. In addition, fleet tests were carried out with six trucks. These covered more than 350,000 kilometers on C.A.R.E Diesel fuel made from 100 percent commercially available HVO. »Again, the results showed no problems in use,« Wagner confirms. Plans for further testing include expanding the fleet and extending the endurance run to 2024. »Tests on a rail engine using R33 and pure HVO also showed the same results as the road tests,« Wagner adds.

Life cycle assessment shows potential benefits

As part of the holistic project concept, the renewable fuels were subjected to a life cycle assessment. To this end, all significant energy and material flows associated with the supply and use chain of reFuels and their fossil counterparts were recorded and evaluated. The life cycle assessment showed that the reFuels have significant CO₂ savings potential.

However, to fully exploit the greenhouse gas reduction potential of electrolysis-based eFuels, 100 percent of the electricity must be generated from renewable sources. The CO₂ required for synthesis can be captured from the air or come from waste gas streams from, for example, biogas and sewage treatment plants or even cement plants. For the technology to become established, it must be possible to operate the PtX plants with a sufficiently high number of full-load hours.

reFuels are produced at KIT

At KIT, various fuel blends were initially produced from regeneratively synthesized fuel components (reFuels) and fossil fuels by means of different processes. These fuel mixtures comply with existing standards. The EN 590 standard applies to diesel fuels, and EN 228 to gasoline. These fuel blends are drop-in-capable, which means they can be used in existing combustion engines. »But we are not satisfied with that yet,« Dahmen emphasizes. »The goal of development must be stand-alone fuels entirely without fossil components.«

KIT has two synthesis plants for the production of reFuels: in the bioliq plant on KIT's North Campus, for example, straw is processed to produce synthetic gasoline from second-generation biomass, so-called advanced biofuels. Unlike first-generation biofuels, the synthesis of these advanced fuels from biomass does not compete with the cultivation of food and feed on agricultural land.

»We need to avoid the plate-or-tank discussion. That's why we are focusing on feedstocks that are not in this conflict,« says project coordinator, Dr. Olaf Toedter. In the neighboring Energy Lab 2.0 of KIT, eFuels are produced from the electrolysis of water with the help of regeneratively generated electricity and CO2. The main target is kerosene, but diesel and gasoline fractions are also produced. The CO2 produced during the combustion of eFuels is offset by using CO2 from the ambient air or from biogenic sources for their production.

The »refuels – Rethinking Fuels« project

The project has been taking a holistic view of the production and use of renewable fuels since January 2019. Such fuels can power existing combustion engines in the future - in passenger cars, commercial and rail vehicles, and aircraft. Six KIT institutes are working together with numerous partners from the energy industry, mineral oil, automotive, and supplier industries under the umbrella of the Automotive Industry Strategy Dialog of the state of Baden-Württemberg on the provision and introduction of reFuels. Two pilot and further pilot plants of KIT supplied regenerative fuels, which were prepared, characterized, and tested in experimental engines. Thus, synthesis processes for reFuels could be optimized to reduce crude emissions.

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