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. However, flash point problems occur, in case the alcohols have too low boiling points. Some alcohols could be identified to reach the demands of the specification. Additionally, tests regarding the compatibility of materials and engine tests to monitor regulated and non-regulated emissions were carried out.
In the result, some blends from biodiesel, diesel fuel and alcohols tend to be appropriate to suppress chemical reactions in the fuel and probably in the engine oil. Further research is necessary to explain the chemical interactions that are responsible for the formation of oligomers and their reaction products. Not only chemical but physical bonds can play important roles and are in the focus of current research.