Are biofuels thermodynamically sensible?

16.12.2020 14:08

Biofuel E10 affects car filter systems in the long term

Sandro Abbate Office for press, communication and marketing
University of Siegen

Research group of the University of Siegen and Fraunhofer UMSICHT examined the effects of biofuels on filter systems in gasoline engines in long-term tests.

For almost ten years now, drivers have been able to refuel their vehicles with E10 fuel, provided they have a gasoline engine. But how does biofuel get along with the filter system of vehicles? Investigations by TÜV Nord and the Swedish TÜV have already shown that after long-term use of fuel vapor retention systems (KDRS) with biofuels, more failures can occur. In a four-year long-term test, researchers from the University of Siegen and the Fraunhofer Institute UMSICHT examined the effects of fuel on filter systems. Their results confirm that KDRS are not suitable for long-term use in vehicles permanently fueled with E10 under the test conditions under consideration.

As part of the research project, scientists led by Prof. Dr.-Ing. Thomas Seeger (Institute for Fluid Dynamics and Thermodynamics at the University of Siegen) KDRS scientifically investigated under realistic conditions. To put it simply, a KDRS is a plastic container filled with activated carbon in which gasoline vapors and volatile hydrocarbons (VOC) are adsorbed when the engine is at a standstill or when the engine is idling. When the engine is running, the KDRS system is switched over depending on the operating point. The carbon is flushed in the filter with moist ambient air, as this desorbs the gasoline vapors from the carbon. The purge air enriched with VOCs is then sucked in by the engine and burned there.

Using a modern optical measurement method (RAMAN scattering) developed by Prof. Seeger, the researchers gained the necessary knowledge about the exact composition of the gas phase (purge air and VOCs). They then examined the adsorption behavior of the activated carbon samples in several long-term tests. The test system was used to automatically measure an activated carbon, which is often used in KDRS, over several hundred loading and unloading cycles. It is assumed that around 350 defined test cycles (adsorption and desorption = 1 cycle) correspond to the service life of a car or a distance of at least 200,000 km. For each cycle, the investigation methods used recorded the ongoing ad and desorption process of the coal container in detail. "Since real gasoline is a complex mixture with over 200 different hydrocarbon components that cannot be analyzed at the same time, we needed a simple fuel for the investigation to replace this mixture," explains Prof. Seeger. "For this we use n-pentane as a gasoline substitute fuel, to which E10 has been added corresponding to ten percent ethanol."

Several long-term experiments were carried out in different combinations. Particularly clear results were obtained in the experiments with pure n-pentane (E00) and dry purge air as well as with substitute biofuel (E10) and 70% relatively moist purge air. While the activated carbon filters remained suitable for a long time when using pure pentane and dry purging air, it was possible to determine with E10 with moist purging air that the filters no longer have sufficient adsorption capacity after several hundred test cycles. Accordingly, they cannot be used for the entire life cycle of a vehicle if these activated carbon canisters of the KDR systems are operated under similar test conditions. It would therefore make sense to check the KDR systems regularly - as part of the usual general inspection - for their functionality while the vehicle is in operation. So far, the KDR systems have only been examined once before they are installed.

The research project was carried out jointly by Fraunhofer UMSICHT and the University of Siegen with the support of a project-accompanying committee made up of automobile, activated carbon, activated carbon filter manufacturers, bioethanol manufacturers and analysis laboratories. The project was funded by the Federal Ministry of Food and Agriculture (BMEL), represented by the Agency for Renewable Resources (FNR), under the funding numbers 22403015 and 22403115.

Scientific contact:

Prof. Dr.-Ing. Thomas Seeger
Phone: 0271 / 740-3124
Email: [email protected]

Features of this press release:
Electrical engineering, mechanical engineering
Research results, research projects