Technical Committee Automotive Fuels
Biofuels - Properties and Experiences with their Use - Update
This Research Report is a continuation of DGMK Research Report 611 "Biofuels - Properties and Experiences with their Use" published in 2002.
Since that time the plans of the European commission to promote the use of biofuels have been put in concrete terms. Directive 2003/30/EC sets targets for the period 2005 to 2010, to which extent biofuels have to be marketed. In the case of diesel fuels this will be accomplished mainly by the blending of up to 5% fatty acid methyl esters and not by their use as a pure compound. Ethanol and ethyl tertiary butyl ester (ETBE) are available as blending components for petrol. For both diesel fuel and petrol the existing standards limit the addition of the oxygen containing compounds.
Because of their poorer storage and oxidation stability there is an interest in laboratory tests, which permit to forecast whether biodiesel and diesel fuels containing biodiesel will have a stability that is sufficient for their actual use. Method ASTM D 4625 with storage at 43°C is generally regarded as the most suitable test procedure for the determination of the storage stability of middle distillates. For fatty acid methyl esters and their blends, however, it is less well suited. Amongst the many tested methods for the determination of the storage stability the Rancimat method has got the broadest acceptance. There are, though, results that let it appear questionable, whether a general relationship exists between the Rancimat results and the storage stability.
There are a few diesel fuels, which appear to be poorly suitable for blending of even the small quantity of 5% biodiesel. For such diesel fuels an especially small Rancimat induction period seems to be characteristic.
Not all proven antioxidants for hydrocarbons are also equally effective in blends with biodiesel.
According to previous experiences there are no problems with the use of fuels containing biodiesel in cars, if the biodiesel content does not exceed 5%, water is absent and the storage time does not exceed 6 months. The biodiesel must meet the requirements of standard EN 14214. Unnecessary contact with air by e.g. agitation has to be absolutely avoided.
No difficulties will arise in the practical operation, if ethanol or ETBE are added to conventional petrol within the limits specified in the standards. Attention must be paid, however, to the absence of water in the system. In the case of an uncontrolled mixture of an ethanol containing fuel and an ethanol free fuel it is possible that the vapour pressure specification will be exceeded.