Long -term storage of b0-b20 blends - A chemical and a microbiological study

The Latest Standard EN 590 stipulates inclusion of up to 7% of Fatty Methyl Esters (FAME) in automotive diesel fuel. FAME may consist of unsaturated fatty acids, which are prone to auto and microbial oxidation by exposure to air and water. Both can influence the quality of the blends during long term storage. A chemical study was intended to assess whether FAME-diesel blends (B0, B5 and B20) remain stable during long-term storage, with and without additives. Three different additives were assessed: a package of biocide with a stabilizer additive, meeting the requirements of MIL-S-53021 (A), a FAME-specific antioxidant (B) and a mixture of A+B. Sets of blends and additives were stored in sealed standard drums. The storage stability of the mixtures was assessed by EN 15751 tests. The results suggest that B5 and B20 remain stable for more than 42 months, when treated with a mixture of additives A+B. In a separate microbial study, the same blends and additives were stored for one year, under conditions favoring the proliferation of hydrocarbon utilizing microorganisms. The results suggest that FAME-diesel blends do not support excess microbial growth, as compared to neat diesel fuel under the experimental conditions. It was found that these blends may be stored for one year without additives. Contrary to that, the acidity of B-20 blend with additive (B), increased significantly, as measured following one year of storage. This increase was accompanied by excess fungal growth.