The aim of this paper is the assessment of the possible impacts of eco-friendly fuels on injection systems by conducting tribological model tests. In this regard, lubricity (High-Frequency Reciprocating Rig, HFRR), scuffing load at different temperatures, and oxidation stability of different fuels B7, R33, pure HVO, and commercial-grade HVO diesel fuel have been deeply investigated.
As a result of our study, the HFRR wear scar diameter (WSD) shows no distinct temperature dependence for both fossil-based diesel fuels (B7 and R33). In contrast, vegetable-based ones (pure HVO and commercially available HVO-based fuel) reveal lower lubricity with a trend to higher HFRR value when the temperature is increased. The commercial HVO fuel shows, compared to the pure HVO, better HFRR values at all tested temperatures. Nevertheless, all HFRR values still stay within the limits set by the relevant fuel standards EN 590 and ASTM D975.
For all fuels, the scuffing load clearly depends on the temperature. B7 shows the highest and pure HVO the lowest scuffing load for all tested temperatures. At higher temperatures, commercially available HVO shows a similar, or even better, behavior compared to R33. The results indicate that there is no or only weak correlation between the HFRR and the scuffing load. This correlation obviously varies with fuel grades, additives, and other added substances.
HVO shows excellent oxidation stability due to its pure paraffinic character. Fossil fuels are less stable because aromatic hydrocarbons are much easier to crack than paraffins.
Combustion engines will continue to play an important role until the electrification of transportation is fully established. Our results show that alternative fuels like R33 and HVO represent good alternatives for fossil fuels in diesel engines.
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