WASHINGTON - Pieces of the diesel puzzle are falling into place.
The latest: A federal decision to reduce drastically the sulfur in fuel paves the way for more diesel engines to be installed in U.S. cars and light trucks.
Now the question of whether compression-ignition engines can win a European-like share of the U.S. market hinges more on public attitudes than regulatory barriers. To complete the picture, automakers hope to develop diesels that will make Americans forget past objections about the engines' noise and smell.
'I'm a fan of diesels. I hope we can find a way to make them work in American cars,' said Ron Zarrella, president of General Motors North America.
Zarrella was just one of the industry leaders who applauded the EPA's Dec. 21 announcement that diesel refiners must cut the amount of sulfur, a fuel contaminant, to 15 parts per million in most of the country by 2006.
Automakers wanted even cleaner diesel fuel but supported the EPA's position. The petroleum industry favored a less stringent standard of 50 parts per million. The current average is 500 parts per million.
The regulation on sulfur is part of a much larger set of rules that will cut exhaust pollution from large diesel-powered trucks and buses beginning in 2007. The rules cover vehicles with gross vehicle weights (fully loaded) of at least 8,500 pounds.
Each large diesel truck or bus likely will need a catalytic converter and other control equipment adding as much as $1,900 to its cost, the EPA said. Improved fuel is necessary because sulfur would damage the control equipment, the agency added.
But the EPA also understood the likely benefits of the rules for automakers.
'We believe that in the next six or seven years we are going see a big penetration of diesel cars and SUVs, because of CAFE (fuel economy standards) and other reasons,' said Margo Oge, director of the EPA's Office of Transportation and Air Quality.
If she is right, the rules will be a boon not only to makers of catalytic converters and other emissions controls for large vehicles, but also to suppliers of components for diesel engines of all sizes. Already the diesel suppliers are enjoying a boom in Europe, where diesels power one-third of light vehicles. In the United States, diesels account for about 3 percent.
In the United States, automakers are considering using more of the engines, either by themselves or in hybrid combinations with electric motors. All the concept vehicles developed by the Big 3 as part of the federally supported Partnership for a New Generation of Vehicles feature small, efficient diesel engines in hybrid configurations.
This is the second time in two years that automakers found themselves on the same side of a contentious issue as the EPA and environmental groups.
But the latest rules, likely spurring greater diesel use in cars and light trucks, were something of a trade-off for environmentalists. They like diesel fuel economy because it means fewer emissions that may contribute to global warming. But even clean diesels may produce more air pollutants, such as soot and smog-causing gases, than comparable gasoline engines.
Frank O'Donnell, executive director of the environmental group Clean Air Trust, sees the rules as an opportunity:
'You're not going to be able to build a diesel vehicle at all without the clean fuel. If you have the clean fuel, I think the potential is still unknown how clean you can make the diesel.'
The rules are final and will take effect unless Washington politics intervene. The petroleum industry is expected to try to get the new Bush administration to ease the sulfur standard or to get Congress to block the rules.
O'Donnell said the effort would be a good first test of President-elect Bush on the environment. And if the issue is taken up by lawmakers, he said: 'Bring it on. We'll have that fight in Congress. And we'll win.'