Mercedes-Benz car group plans to launch several diesel-powered vehicles in all 50 states as early as 2008, perhaps signaling a broader move to diesels by the industry.
At least two Chrysler group vehicles, the Chrysler 300 and Jeep Grand Cherokee, also could get diesel options.
Four Mercedes models - the E-class sedan, M-class and G-class SUVs, and new R-class sport wagon - are expected to be offered with diesel power.
Just five diesel-powered car models, including Mercedes' E320 CDI and two small diesel SUVs, now are available in North America. But as gasoline prices soar, automakers are taking a close look at diesels, which deliver about 30 percent greater fuel economy than a similar-sized gasoline engine.
Mercedes plans to meet tough new emissions standards that require diesels to run as cleanly as gasoline engines with an injection system that shoots urea - an ammonialike acid - into the exhaust system.
The urea changes oxides of nitrogen (NOx), the precursor of smog, into harmless nitrogen and water. Mercedes calls the system SCR, short for Selective Catalytic Reduction.
"We are working really hard to have the solution ready for the new regulations that will come in 2007-2008," says Eva Lenhardt, head of technology communications for Mercedes Car Group in Stuttgart.
Those new regulations call for light-duty trucks and cars to meet the Tier 2 emissions standard of 0.07 grams of NOx per mile.
Diesels account for fewer than 1 percent of U.S. passenger-vehicle sales, but several automakers are weighing their diesel options.
Conditions are ripe for diesels. Improved technology has boosted performance and reduced noise and smoke.
The introduction of low-sulfur fuel next year will help companies meet tough emission standards. And sustained higher fuel prices have caused carmakers to seek fuel-saving technologies.
Diesels have an advantage over gasoline-electric hybrid powertrains because they are less expensive and less complex to build. And they deliver about the same fuel economy gains as a hybrid.
Mercedes aims to regain its place as the top importer of diesels in the United States, a position it held from the 1960s to the mid-1980s. Mercedes sold about 4,000 diesels in the United States last year, compared with 25,000 for Volkswagen.
Mercedes expects to sell 4,500 diesel-powered E320 CDI sedans in the United States this year. The E-class diesel went on sale here in May 2004. It is the first Mercedes diesel sold in the United States since 1999.
DaimlerChrysler showed how Mercedes plans to integrate the SCR system into cars with the Boxfish bionic concept car it exhibited in Washington.
The SCR system will enable Mercedes to sell its diesels nationwide, Lenhardt says.
This is a critical time for automakers planning to offer diesels. They must choose an emissions strategy soon to give engineers enough time to test the technology.
By 2009, tougher Tier 2 emissions standards will require diesels to run as cleanly as gasoline engines.
The low-sulfur fuel coming next year will allow automakers to fit diesel-powered cars with particulate trap filters.
Mercedes has been developing the SCR system for years and introduced it first on large trucks in Europe in 2002.
The Boxfish bionic concept car DaimlerChrysler showed on June 7 in Washington gave the first clues about how Mercedes plans to integrate the system into cars.
The small coupe has a urea tank mounted in the spare tire well. The tank contains enough urea to enable the vehicle to run cleanly between scheduled service intervals of about 9,200 to 12,500 miles. The tank would be refilled by the dealer at each oil change.
Lenhardt says Mercedes engineers have wrestled with where and how to store urea on cars.
She said the spare tire area has plenty of unused space. "It's not sure yet, but we think it is a good idea to put the system there," she says.
SCR technology enables diesels to meet tough emissions standards, but problems remain:
"We don't have the right solution for passenger cars yet," says Lenhardt. "But if we would install such a system, there would be a warning like the warning you see when you have to take the car for maintenance."
The car also could be programmed to shut down after a specified number of miles if the driver does not have the urea tank refilled, Lenhardt says.
The EPA has not been enthusiastic about urea.
Regulators don't like the system because of the potential for drivers to let vehicles run out of urea. But the EPA won't stand in the way of the technology.
Karl Simon, the EPA's acting assistant office director for the office of Transportation and Air Quality, said the agency would approve a diesel with a urea system.
"It's our responsibility to review (technology) and make sure it meets the requirements," Simon said. "Generally, if the technology meets the requirements of the regulations, it would be certified for sale."
You may e-mail Richard Truett at [email protected]