Contribution of unburned lubricating oil and diesel fuel to particulate emission from passenger cars

In this study we determined particle-bound paraffins in the exhaust of six light-duty diesel vehicles on a chassis dynamometer for different driving cycles and ambient temperatures. The filters containing particulate matter were extracted with dichloromethane in a Soxhlet apparatus, and the paraffin analysis was performed using two-dimensional normal phase high-pressure liquid chromatography (HPLC) coupled on-line to gas chromatography-flame ionization detection (GC–FID). The different molecular mass of lubricant and diesel paraffins facilitated the distinction between diesel and lubricant contribution to the emission. Although all vehicles were certified according to the same emission class, there were considerable variations between vehicles. The study showed that under cold-start conditions the organic mass fraction ranged from 10% to 30% with respect to particle mass and the paraffins from 30% to 60% with respect to the organic mass. With cold engine, falling ambient temperature increased the emission of unburned diesel fuel, whereas that from unburned lubricating oil was less affected. Under warm-start conditions, the ambient temperature had less impact on the emission of paraffins. The emissions were also affected by the operating conditions of the engine: driving cycles with higher mean load tend towards higher emissions of lubricant. The operating conditions also affected the distribution of paraffins: the emission of light paraffins seemed to be lower with higher load in the driving cycle. With an urban and a highway cycle, roughly 40% and 80% w/w, respectively, of unburned paraffins were contributed by the lubricant. Measurements of polycyclic aromatic hydrocarbons (PAH) in lubricating oil showed lubricant to be a sink for PAHs. As lubricant significantly contributes to the organic emission, as shown in this study, it can be assumed that it is also a significant source of PAH emissions.