Effects of storage on the properties of rapeseed oil and alcohol blends

Kinematic viscosity and density are important fuel properties because they influence fuel atomisation during injection into the engine cylinder. The viscosity and density of neat vegetable oils usually are too high to allow optimal use of these oils in compression ignition engines. Blending vegetable oils with alcohols can improve these properties, but it is not known whether the blend properties remain stable during storage. This study measured kinematic viscosity (at 40 °C), density (at 15 °C) and surface tension of rapeseed oil-alcohol blends that had been stored in closed borosilicate glass bottles at room temperature in the dark for 49 weeks. The values were compared with those of the fresh blends. Further measurements of oxidation stability for the rapeseed oil and the blends were taken after 72 weeks of storage. The blends consisted of rapeseed oil with ethanol at 5 vol–%, and rapeseed oil with 1–butanol at 5 vol–%, 10 vol–%, 20 vol–% and 30 vol–%. All in all, the observed changes during storage were small. Density values deviated by less than 1%, surface tension by no more than 3% and kinematic viscosity differed from the fresh blends’ values by 1% to 8%. Surface tension had increased in some blends and decreased in others. Kinematic viscosity rose in all blends, with the smallest increase measured for the rapeseed oil–butanol 30 vol–% blend. This blend also showed the best oxidation stability, which was close to six hours.