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The introduction of fatty acid methyl ester (FAME) into the diesel pool has led to an increase in the incidence of diesel fuel filter blocking. In contrast to conventional diesel, filter blocking events can occur above a fuel's Cloud Point (CP). It has been shown that this phenomenon is due to trace levels of impurities carried over from the original oil source into the final fuel. The two species identified as being the main cause of the filtration problems are saturated monoglycerides (sMG) and sterol glucosides (SG). Reported in this paper is an extensive study completed to understand the impact that these impurities have on the filterability of FAME and FAME containing fuels. This has been investigated using laboratory based filterability tests that incorporate a specific cold soak and the critical contaminant levels causing failure have been determined.

A joint program was undertaken to evaluate the use of Middle Distillate Flow Improvers (MDFIs) in diesel fuel to ambient temperatures as low as -40°C. The objectives of the program were to (i) study MDFI effectiveness at preventing fuel filter blockage due to excessive wax formation at temperatures below -30°C, and (ii) determine the effectiveness of Low Temperature Filterability Test (LTFT) laboratory procedure in protecting vehicles these extremely low temperatures. A total of seven fuels were blended (including 4 treated with MDFI additive) and subsequently tested in three heavy duty trucks in an all weather climate controlled chassis dynamometer facility. Overnight soak temperatures were as low as -40°C. Two of the trucks were equipped with an engine that was known to be critical for fuel filter plugging due to excessive wax formation. A total of 14 valid vehicle tests were run over a six-day period.