The demand for higher blending rates of biogenic fuels in the international market takes them into focus more and more. Currently, the biogenic components in diesel fuel are covered mainly by fatty acid methyl ester (FAME). When using these biofuels various problems have been observed, which are mainly caused by the lower oxidation stability of FAMEs. Through strong fuel aging effects, the function of a fuel supply system in the car - from the tank to the injectors - are severely affected or at worst a failure of the internal combustion engine occurs.
For this reason, the Institute for Powertrains and Automotive Technology of the Vienna University of Technology evaluated the problem areas in this field systematically in the project " High FAME " together with its partner BMW engines Steyr GmbH.
In a first step, a heated and aerated tank system has been designed and constructed to explore the aging of fuels under defined conditions.
The thus aged fuels were then subjected to an examination at the test bench.
With the developed tank system larger amounts of fuel were aged in drastically shortened time. The resulting behavior of the fuel showed a good similarity regarding the parallel aging processes in vehicles at BMW. The developed fuel aging system thus is an innovative tool designed specifically for the study of biogenic fuels.
On the one hand, it was found that increasing FAME content in the fuel has a higher impact on fuel aging effects. On the other hand, it was also proofed that the starting product for FAME (for example, SME or RME) has an equally significant impact on the aging and thus the engine behavior. In addition, the torque at the full load decreases slightly due to the lower heating value. Finally, it was found that only from a certain age (induction time of measured value) problems at the motor can be expected: Lower aging values than this limit showed no noticeable differences in behavior. Within long testing phases over a period of 200 hours with strong aged FAME blends the influences of polymerization of the aged FAME fuel to the effects of sedimentation were demonstrated at various engine systems. Within this context, the fuel injectors were found to be particularly vulnerable components.