Abstract
Keywords: diesel engines, biofuels, FAME, fuel aging, emissions
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 are susceptible to oxidation and to changes of other essential parameters during aging processes, which have an essential influence the NOx emission. This feature lowers the quality of biodiesel parameters during storage, distribution and application in engines. 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. In spite of the presence of antioxidative additives, the RME was characterized by faster aging than the diesel fuel. Most of all compounds of acid and gum types are created during aging which results in an increased acid number. The highest rise in the acid number belongs to RME. The fastest RME aging is due to high temperature, and, in the second order, to the contact with air. The influence of those factors for diesel fuel is inverse one. In similar aging conditions, the increase of value of the acid number for RME containing additives is greater than for pure diesel fuel and diesel fuel with additives. The aging of the RME with antioxidative additives and its mixtures with diesel fuel cause only the viscosity increase and practically does not introduce any changes of other parameters at the low temperature. The water presence intensifies the process of the RME aging, especially in longer contact. The aged RME is more active with relation to elastomers than the fresh RME with standard parameters. 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 sprayed fuel, which results in increased emission level. Prevention of viscosity changes is an efficient way of the NOx emission decrease.