Search Results

The European diesel fuel specification limits the biodiesel content to 7 %. It is, however, desirable to increase the amount of renewables in the transport sector; therefore blending with a higher biogenic fuel content is of interest. Blending of fuels can lead to chemical reactions between fuel components and may result in undesired products. In detail, aged biodiesel from unsaturated FAME and fossil diesel fuels can form oligomers and precipitations with a maximum in the range of B10 to B20. Precursors are oligomers that can be separated from the biodiesel or the blends in an amount of up to 20 %. These oligomers are soluble in the fuel, but they seem to have potency for chemical reactions with fuel components or the engine oil. To prevent tentative problems in the fuel filter, the injecting system and the combustion process itself, the formation of oligomers should be disabled in blends. Alcohols have been proven and tested to dissolve precipitations in the fuel.

Ecological aspects, the finiteness of fossil resources and the effort to maintain the agricultural structures motivate the use of renewable materials. Since the seventies, the German Federal Agricultural Research Centre (FAL) has been dealing with the technical use of rape seed oil as alternative fuel. It was easy to demonstrate that pure rape seed oil is not suitable for long-term use in conventional diesel engines, because of the severe engine troubles that occurred. Nevertheless, the use of rape seed oil is possible if either the engine concept or the fuel is changed. Via a different combustion concept or the transesterification of the rape seed oil - mostly to rape seed oil methylester (RME) - rape seed oil can successfully be used as fuel. RME resembles diesel fuel (DF) in its physical properties. Since 1982, an agricultural tractor with unmodified engine has been running in a long term experiment at the FAL. No problems caused by this fuel have occurred.

In Germany 100.000 tons of biodiesel (rape seed oil methylester, RME) were produced in 1998. 200.000 tons are expected in 2000. Therefore, it is necessary to judge the environmental and health effects deriving from the use of RME in combustion engines. The analysis of particle size and particle number distributions of diesel soot and the determination of its mutagenic effect were investigated. Additionally, emissions of ozone precursors were analyzed for both fuels. Finally, regulated and some important non-regulated emissions from different blends of RME and fossil diesel fuel were determined.