Diesel Fuel Lubricity Comparisons with HFRR and Scuffing Load Ball-on-Cylinder Lubricity Evaluator Methods, part II 2015-24-2498
The sulphur level of diesel fuels began to be limited in Europe at the end the 20th century. Quite soon after that it was noticed that the processes for removing sulphur also removed other polar compounds and the natural lubricity of the diesel fuel was lost. Lubricity additives were introduced to restore lubricity properties. Also, a rapid laboratory method was developed to measure lubricity i.e. High Frequency Reciprocating Rig (HFRR). The method (HFRR) ISO 12156-1 was introduced in 1997 and included in EN 590.
In recent years purely paraffinic diesel fuels, such as GTL (Gas To Liquid) and renewable HVO (Hydrotreated Vegetable Oil), have been introduced to the market. Unlike traditional biodiesel (FAME, Fatty Acid Methyl Ester), paraffinic diesel fuels require the use of lubricity additives to reach a sufficiently high level of lubricity.
In this study two methods were applied in testing lubricity: HFRR and SLBOCLE (Scuffing Load Ball-On-Cylinder Lubricity Evaluator) on diesel fuels with aromatic levels between 0 and 14.5 wt.-%. Two types of lubricity additives (with different dosing rates) were included.
The aim of this study was to investigate how the current lubricity additives perform in diesel fuels with varying aromatic content and to compare the reliability of the two test methods HFRR and SLBOCLE
The results from the HFRR values were logical; the HFRR values got better with an increasing additive dosing level rate in all aromatic levels while in contrast the SLBOCLE results were inconsistent. SLBOCLE values did not for all samples improve with an increase in lubricity additive. These observed SLBOCLE results thus supported the previously published work that repeatability and reproducibility of this method needs to be substantially improved.
In addition, according to the results from this study, there is no evidence that low or zero aromatic content diesel fuel is more critical for lubricity than higher aromatic containing diesel fuels. Adequate lubricity can be achieved with conventional lubricity additives regardless of aromatic level of diesel.