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Ricardo testing finds DPF regeneration spikes particulate emissions, resulting in exceedance of Euro limits

Testing of two popular Euro 6d-temp diesels by Ricardo, commissioned by the environmental NGO Transport & Environment (T&E), has found that the periodic regeneration of diesel particulate filters (DPFs) in the light-duty vehicles can generate spikes of particulate emissions of more than 1,000 times the normal rate.

This results in exceeding the particle number emissions limit by between 32-115% on all tests in which a full DPF regeneration occurred. However, current Euro regulations do not apply the legal limit to regeneration tests.

Ricardo tested a Nissan Qashqai and an Opel/Vauxhall Astra. The Nissan was the second-best-selling car in the class C SUV segment, and the Opel/Vauxhall was the fourth-best-selling in the C segment in Europe in 2018/19.

The laboratory tests simulated real-world driving and measured a range of pollutants including those which are currently unregulated and difficult to measure on the road, such as ultrafine particles, volatile and semi-volatile particles and ammonia. The results were compared to official type-approval data where available.

The main findings are:

  • The cars would have exceeded the legal limits for the number of particles emitted if these emissions were not ignored by the EU emissions standard. All tests during which a regeneration occurred witnessed a steep increase in the number of regulated particles compared to tests in which a regeneration did not occur. The particle number emissions limit of 6x1011/km for solid particles larger than 23nm was exceeded by between 32-115% on all tests in which regeneration occurred.

  • Both models respected legal limits for gaseous pollutants and particulate matter (nitrogen oxides, carbon monoxide, total hydrocarbons, total hydrocarbons and nitrogen oxides, particulate matter). However, during regeneration, emissions of all of these pollutants increased significantly.

  • The regeneration blind spot in regulations mean that between 60-99% of emissions of all regulated particles is ignored for the two test cars.

  • A large proportion of particles are not even measured today but constitute a serious health risk. Currently only solid particles which are larger than 23nm in diameter are regulated. However, when solid particles as small as 10nm were measured the total PN emissions increased by between 11-184% compared to when only regulatory particles were measured. This means that large amounts of particle pollution are completely neglected from a regulatory point of view, despite potentially being the most harmful to human health.

  • Regeneration events for the Astra occurred almost twice as often as during type- approval. The distance between two DPF regenerations was 419 km for the Astra; this is almost half of the distance determined at type-approval. A similar distance of 423 km was determined for the Qashqai.

T&E estimates that there are approximately 45 million diesel cars fitted with a DPF in the EU21. Given that the average EU diesel mileage is estimated to be between 13,600 to 23,200 km, a DPF regeneration is estimated to occur, on average, every other week for most diesel cars—or 1.3 billion times each year in the EU.

These results suggest that DPFs are not the definitive solution to the diesel particle problem many had suggested, and instead can cause substantial peaks of air pollution during real-world driving conditions, T&E asserted.

For public health, what matters is the actual emissions from the vehicle, not only whether an emissions limit measured using a specific test is met. The results of this test programme suggest that the newest Euro 6d-temp diesel cars respect legal limits within the boundary conditions of regulatory tests but that there are still serious gaps in the new regulatory tests that fail to capture all driving conditions and spikes in particle number emissions. There are also a number of harmful pollutants that are entirely unregulated.

—“New Diesels, New Problems”

T&E said lawmakers must accept that diesels are still highly-polluting and should make emissions limits and testing more stringent.

T&E said the new European Commission should also use its new powers to require type approval authorities to check cars on the road, after they have been sold—as the US Environmental Protection Agency does.



According to the linked T&E report - "...Combining the per km impact of regeneration on regulatory PN emissions with regulatory PN results on non-regenerating tests did not result in an exceedance of the 6 x10^11/km PN limit. This is also the case when the same calculation is performed for particles larger than 10 and 4nm...." (Page 28)

In fact, both vehicles tested easily met the 6X10^11/km standard (<2X10^11/km), even accounting for the more frequent active regenerations claimed in the report and using the smaller particle sizes.

There's nothing in the regulation stating that the 6X10^11/km standard is a "not-to-exceed" one.

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