July 9, 2001

B-Net

Filter-Equipped Diesels As Good Or Better Than Gasoline, Propane, Cng Or Pm Emissions:
More Proof In Studies Jack Peckham

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Studies by Swedish National Road Administration and the UK Department of the Environment, Transport & Regions (DETR) once again confirm that diesel vehicles and engines equipped with high-efficiency particulate matter (PM) filters can meet or beat the PM emissions of gasoline cars and propane or compressed natural gas (CNG) engines.

These studies once again contradict claims by certain "greens" that greater dieselization automatically represents a worse health risk, or that CNG mandates are preferable to green-diesel technology with particulate matter (PM) filters.

Highlights of the two studies:

* The Swedish study of 45 different light-duty cars, vans and pickups covered both turbocharged and naturally-aspirated spark-ignition (gasoline) cars, gasoline direct injection (GDI) cars, direct-injection diesels and the PSA/Peugeot 607 car equipped with the world's first PM filter-equipped diesel production engine (pioneered with cerium additive/PM filter combo proponent, Rhodia).

The tests on chassis dynamometers used Swedish Class 1 ultra-low-sulfur diesel fuel (ULSD), similar to the 10 ppm ULSD that is phasing-in throughout Europe from 2005 and the 15 ppm ULSD mandated in mid-2006 in North America. ULSD aids PM trap regeneration and reduces sulfate PM emission.

"The diesel plus filter vehicle [PSA 607] emits between 100 and 10,000 times less ultrafine particles per gram of fuel used than the diesel engines without filters, and emits considerably fewer particles than most of the spark-ignited [gasolinej engines," according to the recent Swedish National Road Administration report. (See: www.vv.se/publ_blank/bokhyllalmiljo/emi/intro/htm, or DieselNet.com).

This follows similar findings by Germany's UBA (similar to U.S. EPA) that PM trap-equipped cars have nearly identical "total relative carcinogenic potential" as gasoline cars with three-way catalysts (see Diesel Fuel News 8/23/99, p9).

It also follows on studies from United Kingdom showing that gasoline car PM is even smaller (and thus potentially carries greater health threats) than diesel car PM (see Diesel Fuel News 8/20/98, p9).

"Vehicles with petrol [gasoline] engines tend to produce more smaller particles compared to those produced from vehicles with diesel engines," the study found, confirming the earlier UK studies.

"The results show that the French particle filter [PSA/Rhodia system] very efficiently removes ultrafine particles from the exhaust," the Swedish study shows. "In many conditions the number of particles emitted from the Peugeot 607 Hdi is lower than the numbers emitted from the cars with turbo SI [gasoline] engines."

* GDI 'Even Worse'

This confirmation of clean-diesel environmental performance is vindication for PM filter proponents. "I am not at all surprised by [the report's] content," explains Rhodia's Jacques Lemaire, a leading proponent of PM trap technology for emissions control. "It is obvious that gasoline cars produce some PM, therefore their emissions are more than ambient air, and this would be even worse with GDI."

By contrast, the filter-equipped Peugeot captured all sizes of PM and even produced lower PM emissions than ambient air in several tests.

What's more, the filter-equipped diesel PM emissions "were lower than all of the SI DI [GDI cars], most of the turbo SI and some SI NA [naturally-aspirated] vehicles under moderate driving conditions," the Swedish study found. "If fitting particle filters to diesel vehicles becomes widespread practice, [then] petrol [gasoline] vehicles could become the major source of ultrafine particles."

* The UK DETR study (www.ricardo.com/downloads/SummaryReport.pdf), in cooperation with UK automakers (SMMT) and the European oil industry environmental research division (CONCAWE) once again shows the beneficial effect of ultra-low-sulfur diesel (ULSD) combined with PM filters.

In tests on both light- and heavy-duty vehicles and engines, diesel engines with PM filters matched or outperformed all the other gasoline, propane and CNG technologies on particle emissions. Extra benefit comes from the [less than]10 ppm sulfur Swedish Class 1 ULSD as compared to the [less than]50 ppm UK ULSD. That's because the even lower sulfur level in Swedish diesel produces fewer volatile sulfate emissions than the sulfate emission from UK ULSD.

Sulfate accounts for most of the "volatile" particles, the study shows, along with certain low-volatility hydrocarbons and water vapor. These volatiles slip by PM filters at high-load conditions. Gasoline, LP-gas and diesel PM emissions (from PM filter-equipped engines) are similar in both PM mass and composition, the study shows.

The PM filter-equipped diesels outperform the gasoline or LP-gas engines on PM number emissions at lower speeds, while gasoline and LP-gas produced lower PM emissions at higher speeds.

Filter-equipped diesel engine PM mass emissions over Europe's R49 and Euro Steady Cycle (ESC) from the PM filter-equipped diesel "were less than those from the CNG engine over the ETC [Euro Transient Cycle]," the report found.

The report recommends further studies on PM filter efficiency durability, along with comparisons of emerging aftertreatment devices such as plasma-catalysts and electrochemical devices. New research should also look into emissions effects with fuels and lubricants "where sulfur level has been reduced as close to zero as possible."