Influence of the fatty acid spectrum of vegetable oil methyl esters as pure fuel and blends on the emissions from diesel engines

Biodiesel (in Germany usually rapeseed oil methyl ester, RME) is used as a neat fuel as well as in blends with mineral diesel fuel (DF). Thus, in 2008 in Germany a total of about 2.7 million tons (about 3.1 billion litres) of biodiesel were sold, of which 41 percent was used as a neat fuel and 59 percent in blends. Since then, because of the tax regulations, the proportion of neat fuel in the total biodiesel sales fell to below 10%. Currently, a maximum of 7 percent biodiesel in diesel fuel is allowed (B7 Blend). The quality requirements for B7 are described in DIN 51628. Because of the limited availability of fossil resources, an increase of biogenic compounds in fuels is desired. To achieve this goal, next to rapeseed oil, other sustainably produced vegetable oils can be used as raw materials. These raw materials influence the fuel properties as well as the emissions. For blends, the emissions are not necessarily a reflection of the percentage emissions of the underlying pure fuels. To investigate the environmental impact of the exhaust gas, it is necessary to determinate next to the regulated exhaust gas components (nitrogen oxides, particulate matter, carbon monoxide and hydrocarbons) further non-regulated components. In detail, particle size distribution, emissions of polycyclic aromatic hydrocarbons, and mutagenicity in the Ames test are of special interest. These emissions can not be derived from the regulated components. In this paper emission measurements on a Euro III engine OM 906 of Mercedes-Benz are presented. As fuel vegetable oil methyl esters from various sources (rapeseed oil, soybean oil, palm oil, coconut oil and linseed oil) and reference diesel fuel were used as well as blends of the vegetable oil methyl esters with diesel fuel.