Aging processes of biodiesel and biodiesel/diesel fuel blends

There has been increasing interest in recent years in the use of biodiesel as a substitute for petroleum-based diesel fuel. Fatty acids methyl esters (FAME) in a pure form are applied as a biodiesel B100 or as blends with diesel fuels named as the B10 biodiesel, the B20 biodiesel etc. FAME is susceptible to oxidation and to changes of other essential parameters during aging processes, which have an essential influence the NOx emission. Change of biodiesel parameters results in deterioration of fuel working properties and in increase of the NOx emission level. The increased NOx emission level is accompanied with high viscosity. Experiments with the PDPA laser-equipment showed that high content of biodiesel in a fuel increases the Sauter Mean Diameter (D32) of a fuel spray. The Sauter Mean Diameter increases with time of the aging process of biodiesel, what additionally can unfavourably influence the level of emission of exhaust gases. The research results of samples of aging processes of Rapeseed Methyl Ester (RME) accomplishing requirements of the EN 14214 European Biodiesel Standard, diesel fuel accomplishing requirements of the EN 590 (for based diesel fuel and blends of based diesel fuel and RME containing 1%, 5%, and 20% RME) are presented in the paper. Determination of influence of the fuel properties and the aging process on the acid number, kinematic viscosity, cloud point, cold filter plugging point, and pour point of fuel samples was an aim of performed research, as well the aging RME effect on elastomers comparatively with fresh RME. The process of fuel samples aging was enforced by the daylight (sun) effect, air, the elevated temperature and water. Fuel samples were aged in laboratory conditions during 15 and 60 weeks. Then the changes of fuels properties with relation to the same properties in initial conditions were determined. The water presence intensifles the process of the RME aging, especially in longer contact. An essential novel aspect of the paper is a relation determined between changes of biodiesel properties during aging and the NOx emission level that is connected mostly with increased viscosity. Rise of viscosity increases size of droplets of spray ed fuel, which results in increased emission level. Prevention of viscosity changes is an efficient way of the NOx emission decrease.