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Diesel Fuel Lubricity Comparisons with HFRR and Scuffing Load Ball-on-Cylinder Lubricity Evaluator Methods
Abstract:
Diesel fuel requires sufficient lubricity to prevent excessive wear in fuel injection equipment. The processes for removing sulfur from diesel fuel also eliminate compounds that are responsible for its lubricating properties. This phenomenon is counterbalanced by employing lubricity additives to restore fuel lubricity to an acceptable level.
The aim of this study was to compare the two different laboratory methods for testing lubricity. The two methods were the EN 590 standard method high frequency reciprocating rig (HFRR) and a less utilized method scuffing load ball-on-cylinder lubricity evaluator (SLBOCLE). Two different commercial lubricity additives were used. In addition, rapeseed methyl ester (RME) was used for lubricity purposes in the same way as the additives. To study the possible effect of the base fuel, the tests were performed with fossil diesel fuel, paraffinic diesel (Hydrotreated vegetable oil, HVO), and a blend of these.
The best HFRR - SLBOCLE correlation was found with RME used as a lubricity additive, but the results were still conflicting concerning the approval limits. With the commercial lubricity additives, the best correlation was achieved with paraffinic diesel base fuel and acidic type of lubricity additive. Ester based lubricity additives gave seemingly random SLBOCLE results while the acid based lubricity additive produced slightly more coherent results. The correlation was poor with all different additives when the base fuel was 100 % fossil.
The results indicate that the correlation between HFRR and SLBOCLE is generally poor. While HFRR showed improved lubricity trend by increasing dosing level of the additive, SLBOCLE did not. The reason for this may be that the methods are measuring two different types of phenomena - wear and seizure. SLBOCLE also seems to rule out fuels which have shown good behavior in the market, if the suggested limit is applied. The writers feel that the repeatability and reproducibility of SLBOCLE method would need substantial improvement.
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