The Effect of Biodiesel Fuel Composition on Diesel Combustion and Emissions

Biodiesel, a fuel produced by transesterification of vegetable oils or animal fats, is receiving increasing attention as an alternative fuel for diesel engines. The properties of biodiesel can vary depending on its chemical composition. Biodiesel produced from vegetable oils is higher in esters of unsaturated fatty acids and biodiesel from animal fats is higher in esters of saturated fatty acids. This paper attempts to identify the mechanism for biodiesel's emissions reduction effect and discusses the effects of blending various pure esters with No. 2 diesel fuel on engine performance and emissions. This project concludes that biodiesel's particulate reducing effect can be attributed to two factors: its displacement of aromatic and shorter chain paraffin hydrocarbons and its oxygen content. The pure ester tests showed that while all esters demonstrated reductions in hydrocarbon and particulate emissions, methyl palmitate was the most effective ester in achieving these reductions. NOx emissions increased from 2-5% for the different esters while CO emissions generally decreased slightly or stayed the same. Thermal efficiency did not change for the esters.