Influence of different vegetable oils on diesel exhaust emissions

In last years raw vegetable oil, next to biodiesel, seemed to be an alternative to fossil diesel fuel with high substitution potential. It has positive effect to the environment in the field of climate protection and the prevention of water pollution. Due to economic incentive the marketing was 400 000 tin 2008. Meanwhile the tax increased, the price for fossil diesel fuel is relative low, and therefore vegetable oil has a marketing crisis. Nevertheless, the technical base was developed to use vegetable oil and companies offer conversion kits and tractors. The regulated emissions of engines using vegetable oil are well known, but there are only few and contradictory results concerning non-regulated emissions as polycyclic aromatic hydrocarbons (PAH), particle size distribution and mutagenic effects. In this paper, measurements of regulated and non-regulated emissions of an Euro III engine OM 906, Mercedes-Benz, are presented. Next to diesel fuel rapeseed oil, soy bean oil, palm oil, linseed oil, and coconut oil were used. The vegetable oil was preheated before use. Regarding the regulated emissions, the nitrogen oxide emissions increased and the carbon monoxide emissions decreased using vegetable oil. The emissions of particulate matter and hydrocarbons increased (rapeseed oil, soy bean oil, linseed oil) or stayed unchanged (coconut oil, palm oil) in comparison to diesel fuel. PAH emissions and the mutagenic effect increased by factor 30 using vegetable oil instead of diesel fuel. This increase was predominantly due to transient phases during the test run. If steady state modes were tested only a comparatively moderate increase of PAH emissions and mutagenic effects was observed. Comparing the vegetable oils among each other in the majority of cases coconut oil and palm oil showed the lowest and linseed oil the highest emissions. These findings correspond to the iodine numbers of the fuels.