The diesel dilemma. (WIP).

"Light trucks and SUVs will probably be the vehicles that will start moving diesel into the mainstream with the American public," says Gary Hirschlieb, director, Diesel Fuel Systems Engineering, Robert Bosch Corp. Currently, diesels power just 3% of U.S. light passenger vehicles. "For the domestic automakers that segment has the greatest need and potential for fuel economy improvement given the continuing shift in the market toward these vehicles." And while this may be the segment most in need of diesel's efficiency benefits, VW's experience suggests there is a lifestyle component to diesel sales in North America. The Beetle, Jetta, and Golf-which share a common platform-offer an optional 1.9-liter turbo direct injection diesel [TDI] engine for which VW charges a premium of about $1,200. Golf buyers are most likely to choose the diesel, but an increasing number of Beetle buyers have opted for the oil burner, enough to help stem a sales slide for the model. Plus, says Stuart Johnson, manager, Engineering and Emissions Operations for VW of America, "Jetta buyers see it as something of a lifestyle choice. Its mileage advantage and low emission levels put them on the leading edge with their peers." Unfortunately, attaining the proper emissions performance will become more difficult in the coming years.

As currently written, U.S. clean air registration imposes tighter emission standards on diesel vehicles in 2004. What it doesn't require is that refiners significantly lower the sulfur in diesel fuel until 2006. This gap has the potential to stall large-scale adoption of diesel powerplants until the 2007 model year at the earliest.

Federal "Tier 2" standards require that gasoline and diesel engines meet the same 0.07 grams/mile NOx level, reduce non-methane hydrocarbon output From the current 0.31 grams/mile to 0.125, and cut particulate matter from 0.10 grams/mile to 0.08. California's 2007 standards, meanwhile, reduce these amounts even Further. The question is: Can automakers meet the regulatory challenge?

"Now is the time for the industry to take the next step in aftertreatment technology for the diesel," says Dick Baker of Ford's Advanced Technologies Group. We Face a situation that's very similar to what we Faced 30 years ago with the gasoline engine. So while we may be unsure of how we are going to meet the standards," he says, "we're confident that we will get there."

Working against this, says Pam Jones of the Diesel Technology Forum, is the U.S. government's unwillingness to negotiate a trade-off on diesel emissions. "The U.S. looks at individual pollutants, not aggregate levels," she says, "whereas the Europeans have been willing to balance a reduction in CO, [Co.sub.2], and hydrocarbons-the 'greenhouse gasses'-with a lesser reduction in NOx and particulates." This strict adherence on the part of the EPA has limited the appeal of diesels in the U.S. by ignoring any advantages that might be gained From a systems view of pollution control.

"Americans drive farther and in larger vehicles than any other civilization on the planet," says Jones. "Placing them in vehicles that are significantly more fuel efficient means fewer pollutants are ultimately released into the air. If also gives them the opportunity to choose the vehicles they want to drive, not what some regulation mandates they have to drive."