Forget about electric vehicles, hybrids and fuel cells for the moment. The diesel is the best alternative we have on the horizon. And that's different than I thought a month ago.

Thanks to an in-depth discussion on diesel engines recently sponsored by the Society of Automotive Engineers, I've become convinced the old clatterbox has a new lease on life in the American market.

Diesels are selling like crazy in Europe, thanks to their torquey power, fuel efficiency and low carbon dioxide (CO2) emissions. But over here we've been led to believe they could never meet our stringent emissions standards. Yet the very people who said it couldn't be done have changed their tune.

“We used to say the diesel emission standards were unachievable and would ruin engines,” says John Horne, the chairman of Navistar International. “But everything we said we couldn't do, we did. And the engines didn't get worse, they got better.”

Modern diesel engines sold in Europe are clean and quiet. Unfortunately, the technology needed to make them like that gets clogged up with the high-sulfur diesel fuel sold in the U.S.

But new regulations, starting in 2006, will force refiners to reduce the sulfur content from today's average of about 500 parts per million to 15 ppm. And it's stricter than it sounds.

To account for contamination in pipelines and tankers, it will have to leave the refineries at 8 ppm, and arrive at the pump at 10 ppm. Starting in 2006, the U.S. likely will have the cleanest diesel fuel in the world.

Thanks to this low-sulfur fuel, as well as new lubricants and a concerted effort at systems engineering, diesel manufacturers say big improvements are coming.

“We have V-6 and V-8 engines in the lab today that can meet the Tier II, Bin 5 regulations,” John Wall, chief technology officer at Cummins Engine Co., says about meeting the Environmental Protection Agency's toughest standards. “We are getting them ready for production.”

These standards will force light trucks (including large SUVs) to meet the same oxides of nitrogen (NOx) level as gasoline-powered cars and will slash particulates by 90%.

That's important because a recent study from Stanford University suggests that particulates are a major cause of global warming. The upcoming standards virtually eliminate that problem, says the EPA.

“They will be as clean as the cleanest gasoline and alternate-fueled engines,” promises Margo Oge, director of the EPA's Office of Transportation and Air Quality.

You read right, that means cleaner than engines running on natural gas. She goes on to predict that in the 2010-2020 timeframe, diesels will hit the same market share they now enjoy in Europe.

That would cut U.S. oil consumption by 1.5 million barrels a day, which is twice as much as we currently import from Iraq. And it would boost diesel production by 5.5 million engines a year.

Diesels offer a 25% to 30% improvement in fuel economy, a similar reduction in CO2, and good torque and power. That's why Nick Scheele, president of Ford Motor Co., has said: “The diesel's time has come.”

I still see a marketing challenge with people getting smelly diesel fuel on their hands. But keep an eye on the diesel engine, folks, the bandwagon is starting to roll.

John McElroy is editorial director of Blue Sky Productions and producer of “Autoline Detroit” for WTVS-Channel 56, Detroit.