EPA Driving for More Diesels

DETROIT – Speaking at the recent Society of Automotive Engineers World Congress here, Margo Oge, director of the Environmental Protection Agency’s Office of Transportation and Air Quality, insists the agency is solidly behind efforts to advance the use of diesels for U.S. passenger vehicles.

Mercedes E320 CDI is one of few passenger-vehicle diesels available in U.S.

Oge says diesels maximize energy efficiency. Her position at one time may have appeared counter to the clean-air agency’s mandate, but the EPA’s backing of diesel technology demonstrates the agency is convinced new-age diesels are not the “dirty” engine technology of the past.

Oge makes it equally clear the EPA sees no reason to retreat from the tight federal Tier II diesel emissions standards (notably for oxides of nitrogen) that this year began phase-in and will be fully implemented in 2007. The engineering community appears divided regarding whether – and how – light-duty diesels can comply with the “bin 5” emissions subdivision of the Tier II regulations that is considered vital to volume implementation of diesels for passenger vehicles. (See related story: GM Cautious About U.S. Diesels)

Oge says there is sufficient evidence that Tier II, bin 5 levels can be achieved with emerging diesel technology without the need for NOx aftertreatment.

Asked how the EPA believes light-duty diesels can meet bin 5 without some type of NOx aftertreatment, an industry source tells Ward’s the strategy is to increase fuel injection pressure higher than current common-rail levels of about 26,000 psi (1,800 bar); employ large volumes of exhaust-gas recirculation (EGR) and increase turbocharger boost pressure.

Ward’s is told these measures will reduce diesel combustion temperatures to the levels needed to comply with Tier II NOx mandates – but engine-out particulate (PM) emissions, conversely, will be increased by more than a factor of 10.
These increased PM levels presumably would be controlled by higher-capacity regenerative filters already in use for some light-duty diesels. Sources say this approach is more cost-effective than employing both NOx aftertreatment and particulate filters. (See related story: Rhodia Improves Eolys System, Hopes to Spur Diesel Market)

The cost and fuel-efficiency values for these alternatives are not available, however. One aspect is a new, lower-cost cordierite monolithic diesel particulate filter made by Owens Corning. The new filter design is said to be effective if combined with other advanced control strategies.

Information about the status of current diesel vehicles contained in an SAE paper delivered by EPA engineer Joseph McDonald suggests that five light-duty vehicles “have demonstrated significant progress in NOx and PM emissions control.”
McDonald reports, “The most significant demonstration of progress is the improved durability of catalytic NOx control applied to a small station wagon powered by a 2.8L turbodiesel.”

The test vehicle, McDonald says, is fitted with: high-pressure common-rail fuel injection, a NOx adsorption catalyst, a PM trap, an oxidation catalyst and cooled EGR.

Diesel fuel used for the test vehicle, McDonald’s paper reports, had a 50.8 cetane rating. Diesel fuel with this high a cetane rating – the measure of its propensity to combust – rarely is commercially available in the U.S.

The test vehicle’s emissions barely comply with Tier II, bin 5 standards – but are not adequately lower to allow for manufacturing variations and performance deterioration.

Another difficulty faced by developers of diesels for the U.S. market is cited by Robert Last, vice president-operations and communications for FEV Engine Technology Inc.

“We are in need of a number of experienced diesel engineers to carry out our diesel development work for clients,” Last says, but adds the company is limited on the number of engineers it can bring to the U.S. due to recent visa restrictions.

In effect, he suggests that while there is great public outcry about U.S jobs being outsourced, limits are placed on companies’ importation of employees with critical skills.