Effects of fuel properties on particulate emissions of diesel cars equipped with diesel particulate filters

Abstract

The current study investigates the effect of diesel fuel density, cetane number (CN), polycyclic aromatic hydrocarbons (PAH) and fatty acid methyl ester (FAME) content on the mass, size distribution, and chemical composition of particulate matter emissions from modern light-duty vehicles. Thirteen test fuels were evaluated against a reference one on chassis dynamometer tests of a (non-DPF) Euro 4 and two DPF-equipped Euro 5 and 6 vehicles. Statistically significant differences in particulate mass (PM) and particle number (PN) emissions were observed between all vehicles, including the two DPF-equipped ones. Fuel properties significantly affected particulate emissions and size distribution in almost all cases of the Euro 4 car, while few statistically significant trends were observed for the Euro 5 and 6 vehicles. High fuel density decreased PN emissions of DPF cars over a cold-start test, while a PN increase was observed for the Euro 6 over the same cycle with increasing FAME content. These effects can be attributed to the impact of density and FAME on engine-out emissions and the subsequent rate of DPF filtration efficiency built-up, following regeneration. Those trends were not observed in hot-start testing after sufficient soot had accumulated in the DPF. Finally, PM chemical composition was found to be insensitive to fuel properties in all vehicles. These results imply that DPFs have to a large extent masked the role of diesel fuel properties on particulate emissions, but there is still room for optimization, especially in PN emissions of vehicles with frequent regenerations.