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The lubricating efficiency is an important property of diesel fuel since several diesel engine parts, such as pumps and injectors, are lubricated by the fuel itself only. The evolution of oxidation products during oxidative deterioration may as well affect the lubricating properties of the biodiesel fuel blends and thus the proper functioning of a diesel engine. In this study Fatty Acid Methyl Esters were produced from various types of feedstock that significantly differentiate in their fatty acid profile. Each methyl ester was blended with an Ultra Low Sulphur Automotive Diesel (ULSD) at a concentration of 7% v/v which is currently the maximum acceptable FAME content according to the European Standard EN590. The B7 biodiesel blends were evaluated regarding fundamental physicochemical properties as well as their lubricating efficiency. Oxidation stability was examined on a Rancimat apparatus according to EN 15751 standard.

FAME is the most common renewable component of conventional automotive diesel. Despite the advantages, biodiesel is more susceptible to oxidative deterioration and due to its chemical composition as well as its higher affinity to water, is considered to be a favorable substrate for microorganisms. On the other hand, apart from biodiesel, alcohols are considered to be promising substitutes to conventional diesel fuel because they can offer higher oxygen concentration leading to better combustion characteristics and lower exhaust emissions. More specifically, n-butanol is a renewable alcohol demonstrating better blending capabilities and properties when it is added to diesel fuel, as its composition is closer to conventional fuel, when compared ethanol to for example. Taking into consideration the alleged disinfectant properties of alcohols, it would be interesting to examine also the microbial stability of blends containing n-butanol in various concentrations.

For many years Rancimat was the only standardized method for measuring the oxidation stability of FAME and FAME/diesel blends. However this method is not applicable to pure conventional petroleum products and so the effect of FAME on diesel fuel stability could not be evaluated directly. Recently a Rapid Small Scale Oxidation Test (RSSOT) that covers the determination of the stability of biofuels and petroleum products was developed and standardized. In this study the oxidation stability of seven different types of FAMEs was assessed, either neat or blended with three types of ULSD fuel, by employing both the Rancimat and the RSSOT accelerated oxidation methods. The determinations from either test were analyzed and a comparative assessment of these two method was carried out.

This study describes the effect of different types of biodiesel (fatty acid methyl esters, FAME) on the oxidative stability of low and ultra low sulfur automotive diesel fuels. Eight different samples of FAME were employed to create blends of 2, 3, 4, 5, 7, and 10% v/v with four different types of diesel fuels. The samples were analyzed using the modified Rancimat method (EN 15751). The aim of this paper was to evaluate the impact of biodiesel source material and biodiesel concentration in diesel fuel, on the oxidation stability of the final blend. Moreover, the effect of sulfur content and the presence of cracked stocks in the base diesel fuel, on the oxidation stability of the final blends were also investigated.