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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



I use Shell V Power Diesel in my Euro6, as it has a blend of GTL synthetic diesel and supposedly more cleaning additives. It's more expensive, but in the belief that less soot will load the DPF. I haven't noticed any active regeneration side owning it over the last 6,000 miles. MPG has improved slightly over that time with a cleaner engine.


Hope you decide to buy an EV for your next car. Diesels keep making news for the wrong reasons.


Well, while one can embrace the progress it should still be noted that PN emissions from diesel vehicles are already lower than from any other type with ICE vehicle and tailpipe PN concentrations are mostly lower than ambient levels in densely populated cities. Therefore, future focus on PN should be on other engines/fuels. Moreover, it would be easy to achieve similar incremental improvements simply by improving DPF technology, albeit that there is no driving force for such improvement at the moment.

Less soot might actually decrease DPF filtration efficiency, which could counterweight less frequent DPF regeneration. I am not saying that less soot production has to be negative but the interaction between engine-aftertreatment hardware and fuel is complex. As a side note, I could mention that filtration efficiency is far less for a GPF than a DPF. Thus, while the engine-out PN emissions for a GDI is lower than for a DI diesel, tailpipe PN emissions are higher for a GDI. GPFs tend to "self-generate" very frequently. A lower (average) soot loading decreases filtration efficiency substantially.

Much to your regret, I presume, recent news (i.e. for about the past year) on diesel emissions has been very positive.


Personally, I'm convinced that the stone age was not succeeded by the bronze age for lack of stones. The ICE will be succeeded by electric drives no matter how desperate fundamentalists cling to their "stone axes".
The simplicity and efficiency of an electric motor (EM) with full torque from the first rotation is unsurpassed. The EM shatters anything (with two exceptions) that an ICE may offer; it doesn't stink and its silent.
The only sore point of current electric drives is the battery; range and charging time.
In 2020, three manufacturers are emerging on the market with different cell chemistries. However, two attributes are common to all three: high power charge and discharge and range over 600 miles and that at less mass and volume and reduced prices. I'm looking forward not backwards.


Another current problem with EV fleets is that most e-energy required is currently generated with (CPPs, NGPPs, etc). It is no where 100% clean.

Of course, near future clean REs will progressively replace most NPPs and NGPPs e-generation plants for EVs and will supply e-energy to produce clean H2 for FCEVs.

The transition from ICEVs (2+B) may take another 20-40 years, except in China and Norway, where the transition may be pushed much (up to 50%) faster. North America may require 60+ years.

Improved batteries, FCs and H2 containers will soon be available for small and large electrified vehicles, including trains, buses, trucks, small and large machines and planes.


There are ideas out there which manufacturers can use to clean up their emissions.

You can reduce hydrocarbon levels 23-33%, reducing CO2 emissions by 4.3 tons, CO emissions reduced 38-76% all while increasing mileage by up to 36%.

This is all done by reducing friction and it's done with a single application.


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