Long storage stability of biodiesel made from rapeseed and used frying oil

The degree of physical and chemical deterioration of biodiesel produced fro m rapeseed and used frying oil was studied under different storage conditio ns. These produced drastic effects when the fuel was exposed to daylight an d air. However, there were no significant differences between undistilled b iodiesel made from fresh rapeseed oil and used frying oil. The viscosity an d neutralization numbers rose during storage owing to the formation of dime rs and polymers and to hydrolytic cleavage of methyl esters into fatty acid s. However, even for samples studied under different storage conditions for over 150 d the specified limits for viscosity and neutralization numbers h ad not been reached. In European biodiesel specifications there will be a m andatory limit for oxidative stability, because it may be a crucial paramet er for injection pump performance. The value for the induction period of th e distilled product was very low. The induction period values for the undis tilled samples decreased very rapidly during storage, especially with expos ure to light and air.