Effect of biodiesel saturation on soot formation in diesel engines

To understand soot formation in a diesel engine fueled with different biodiesels, a numerical study was performed using the KIVA-3V code, combined with a multi-step phenomenological soot model. The simulations were used to predict differences in soot formation for three various biodiesel feedstock types. Good agreements on soot emissions were achieved in comparisons of engine experiments and simulations at various engine operating conditions. The experimental data and simulated results showed that the degree of saturation and the oxygen content of biodiesel fuels are the major factors responsible for biodiesel soot production. The reduction of soot mass concentration for biodiesel is achieved due to the suppressed soot formation process and improved oxidation rate compared with diesel. It is observed that the acetylene generated in the pyrolysis of biodiesel is proportional to the content of unsaturated fatty acid methyl ester (the number of CC double bonds). Among the three different biodiesel fuels, the lowest soot tendency was found for the Jatropha Methyl Ester because of its lowest amount of unsaturated alkyl esters through both numerical modeling and diesel engine experiments.