Radiocarbon and Hydrocarbon Analysis of PM Sources During WHTC Tests on a Biodiesel-Fueled Engine

PM in diesel exhaust has been given much attention due to its adverse effect on both climate and health. As the PM emission levels are tightened, the portion of particles originating from the lubrication oil is likely to increase. In this study, exhausts from a biodiesel-fueled Euro 5 engine were examined to determine how much of the carbonaceous particles that originated from the fuel and the lubrication oil, respectively. A combination of three methods was used to determine the PM origin: chain length analysis of the hydrocarbons, determination of organic and elemental carbon (OC and EC), and the concentration of ¹⁴C found in the exhausts. It was found that the standard method for measuring hydrocarbons in PM on a filter (chain length analysis) only accounted for 63 % of the OC, meaning that it did not account for all non-soot carbon in the exhausts. Comparing the chain length method to the ¹⁴C-based method showed that the non-extractable organic carbon originated both from the oil and fuel. Elemental carbon (EC), also known as soot, was found to originate mainly from the fuel. However, excessive amounts of oil in the engine cylinders increased the relative contribution from the oil as well as the absolute emissions of EC. This could either be due to the surplus oil forming soot, or to the soot particles being coated by oil and thereby less efficiently oxidized during the late cycle. The results demonstrate the importance of carefully regulating the amount of lubrication oil reaching the cylinder.