Study finds there is still room for optimization of particle emissions based on diesel fuel properties
Researchers in Europe have found that while diesel particulate filters (DPFs) have to a large extent masked the role of diesel fuel properties on particulate emissions, there is still room for optimization, especially in particle number (PN) emissions of vehicles with frequent regenerations. Their study is published in the journal Fuel.
Although a strong body of evidence has already been established on diesel fuel properties and particulate emissions, this has been based on older vehicle types, without diesel particle filters (DPF) in their large majority. The few cases on DPF-equipped vehicles mainly refer to Euro 5 cars/engines or experimental Euro 6-compliant engines and test set-ups, but no clear evidence οn market Euro 6 vehicles is available.
Compared to Euro 5, Euro 6 vehicles are equipped with more advanced aftertreatment systems, including deNOx control and optimized DPFs. In addition, diesel fuel effects on PN emissions have been barely investigated, after the establishment of relevant PN standards in the EU. Since latest fuel regulations (EN 590 and the FQD) were already established in 2009, it is currently not known whether further fuel refinement could be used in latest diesel vehicle technologies to further reduce PM and PN emissions.
The current study aims at evaluating the individual effects of main diesel fuel properties, including density, CN, PAH and FAME content on emissions of PM and PN from latest technology diesel passenger cars. Three cars were selected, complying with Euro 4, 5 and 6 emission standards, covering a wide range of different after-treatment technologies. The selected fuel properties were studied under laboratory conditions on a chassis dynamometer based on a fuel test matrix of 13 diesel blends and 1 reference fuel, which was used as market representative.—Kontses et al.
The study investigated 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.
The researchers found statistically significant differences in particulate mass (PM) and particle number (PN) emissions 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.
The researchers attributed these effects 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.
As a final note, they found that the PM chemical composition was insensitive to fuel properties in all vehicles.
These results reveal that tailpipe particulate emissions and their sensitivity to fuel quality may significantly vary among the different after-treatment systems of modern cars, even among the DPF-equipped ones. Thus, it can be concluded that a refinement of diesel fuel properties can potentially reduce PM and PN emissions of modern vehicles, but the diverse effect among the different after-treatment technologies as well as the secondary impact on regeneration frequency should both be taken into account. In addition, the observed trends should be further evaluated based on even more modern emission control technologies (e.g. Euro 6d-temp and Euro 6d compliant vehicles) in order to examine whether different trends would be observed.—Kontses et al.
A. Kontses, A. Dimaratos, C. Keramidas, R. Williams, H. Hamje, L. Ntziachristos, Z. Samaras (2019) “Effects of fuel properties on particulate emissions of diesel cars equipped with diesel particulate filters,” Fuel, Volume 255, doi: 10.1016/j.fuel.2019.115879