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The interactions of new biofuels and standard engine components are being investigated at the Institute for Fluid Power Drives and Controls (IFAS) at RWTH Aachen University as part of the research of the cluster of excellence "Tailor-Made Fuels from Biomass". Since modern common rail fuel pumps are fuel lubricated special interest lays on the lubricity of new fuels. At IFAS a High Frequency Reciprocating Test Rig (HFRR) is used to screen possible biofuel candidates with regard to this property. Most of these substances show lubricating abilities similar to those of modern diesel fuels. Nevertheless with 2-Methyltetrahydrofuran a remarkable outlier can be found among the favoured fuel candidates. To unravel the influences of certain molecule structures additional substances were included into the experimental research. By comparing the wear scars of linear alkanes, alkenes and alcohols produced in the HFRR the influence of the molecules chain length and functional group is analysed. This paper gives an introduction to the HFRR test set up and presents the experimental results of the recently screened biofuel candidates.

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In the scope of the cluster of excellence “Tailor-made Fuels from Biomass” new biofuels are developed within an interdisciplinary research approach at RWTH Aachen University. To ensure a safe and reliable functioning of the new fuels in combination with state of the art fuel injection equipment, every fuel has to fulfil requirements regarding its tribological performance, which depends on characteristics like dynamic viscosity and fuel lubricity. Hence, one focus of the cluster lies on the tribological characteristics of the fuel candidates. Biofuel candidates which have been investigated so far and which are suitable for the use in self-ignition engines as surrogates for fossil diesel fuel tend to have lower viscosities and show varying lubrication behaviour, compared to diesel. As a standard test method for diesel fuel lubricity the HFRR test is well established. Nevertheless, relying on the established diesel-pass/fail criterion, which is defined in several norms, is disputable, since the investigated biofuels differ strongly from modern diesel fuels. To identify the relevant fuel properties and to gain a more detailed understanding of the wear and friction processes within the critical contacts, results of different tribological test methods, including the HFRR test and a disc-on-disc tribometer, are presented, compared and discussed in this paper. In order to estimate the validity of the established HFRR pass/fail criterion for low viscosity biofuels the experimental results are compared to simulation outcomes of elasto-hydrodynamic simulations of the main tribological contacts in a standard common rail injection pump.