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Despite all the hype behind hybrids and fuel cells the last few years, the answer to the riddle of how to get cleaner air and import less oil may come most immediately from a familiar technology: diesel vehicles.

Stricter new U.S. fuel economy regulations were officially passed into law in December - they are expected to be aligned with new Canadian ones in 2011 - and auto makers the world over are looking at diesel vehicles as the quickest and often least expensive way to meet new mileage and emissions rules.

So while there continue to be examples of hybrids, fuel cells and vehicles running on electricity and ethanol at various recent major North American auto shows, the emphatic return of diesel production cars and trucks to this continent for 2008 to 2010 has been one of the big stories coming out of these shows this year.

Diesel vehicles account for about half of all new vehicle sales in Western Europe, where fuel prices average the equivalent of more than $6 a U.S. gallon.

Diesel's 25-per-cent increase in fuel economy over regular gasoline helped keep it in ubiquitous use by North American truckers, which in turn helped maintain its availability on this continent - even when car buyers dismissed diesels as smelly, smoky and clattering underperformers in the 1980s and 1990s.

Yet this perception, as evidenced by more sales, is set to change.

There are a number of reasons behind the renewed push of diesel cars and trucks, including quickly rising fuel prices, cleaner (and less smelly) diesel fuel and impressive performance at the pump and the stop light for new-generation diesels, auto industry analysts say.

The cheaper manufacturing cost of diesels as opposed to hybrids will mean more diesels than hybrids are sold by 2012 in North America, even though hybrids are currently the more popular of the two in the U.S., says a joint study released last year by Ricardo and UBS, a global engineering and financial services firm, respectively.

The report estimates that 15 per cent of the new vehicle market in 2012 will be diesel or hybrid vehicles, with European manufacturers especially benefiting from this trend.

"Diesel has a clear cost advantage over hybrid, even when fitted with the type of complex exhaust after-treatment technologies necessary to meet future, more stringent emissions regulations," the Ricardo/UBS report said.

The percentage of North American drivers expected to be driving an oil burner in the next 10 years is predicted to hit 17 per cent, more than a five-fold increase over the 3 per cent driving diesels in 2007, according to J.D. Power and Associates' annual global diesel light-vehicle forecast released in January.

"In response to strict tailpipe emissions limits, high fuel prices and a growing awareness of greenhouse gas issues among both consumers and policy makers, rising demand for both diesel cars and light trucks is forecast for the North America market," the report said.

Mercedes-Benz's big unveiling in Detroit was a compact SUV powered by a relatively small four-cylinder diesel engine, the GLK Vision concept, which Benz said was a close preview of the upcoming production GLK.

Benz had also previously announced its intention to sell diesel versions of the M-, GL- and R-Class trucks by this fall, helped by new rules mandating low-sulphur diesel fuel that came into effect in 2006 and allowed the company to introduce its BlueTec line of clean diesels to North America.

BMW of North America chairman Tom Purves noted that it's not only diesel's increased fuel economy and range that give it extra appeal. BMW is using the experience it has with diesel engines in Europe, where 67 per cent of the vehicles it sells are diesels, to introduce the award-winning twin-turbocharged, six-cylinder, clean-diesel engine to the 3-Series sedan and to the X5 SUV to North America by this fall.

That will give BMW's smallest sedan 420 lb-ft of torque in the 335d, or only three lb-ft less than the gargantuan 6.0-litre V-12 found in BMW's 760Li, its largest and priciest full-size luxury four-door.

Increased use of various clean diesel systems by auto makers, especially German luxury car manufacturers, is therefore already under way, and will no doubt help these companies achieve higher average fuel economy numbers, given that most companies predict an average 20- to 30-per-cent increase in mileage with these engines.

Detroit-based companies were less enthusiastic about diesel fuel prospects this year, with GM in particular criticizing both governments and fuel companies for not making E85 fuel more readily available to the general public. Still, Mark Maher, GM's executive director of powertrains, said at the Detroit show that a number of alternatives to gasoline are being developed simultaneously, including advanced direct injection and diesel technologies in the short term, with electric cars and fuel cells to follow.

"It's not an option to pick just one any more," Maher said. "We don't see a monolithic fuel like gasoline will continue."

The Chevrolet Volt plug-in electric car has generated much publicity for its promise of mostly gas-free driving, since GM promises 40 miles (64 km) of electric-only operation, with a gasoline backup engine that means it won't strand its driver. Yet, GM's vice-chairman and product chief Bob Lutz said the Volt and other E-Flex plug-in electric series hybrids are a long way off from high-volume production.

"Volt will be about 10,000 units the first year, just to make sure we're prepared for any issues that might come up, and then ramp up production from there," Lutz told a group of auto journalists, noting that there were still significant development issues to overcome before the technology could be optimized for mass market use. "So we're not going to see a wholesale move to electric vehicles right away."

Diesel's main advantage over other alternative fuels like ethanol is that the infrastructure is already in place, said Mike Lynskey, the technical liaison with Ford for BP Fuels. He works with Ford on gasoline, diesel and ethanol projects, usually for vehicles coming five or six years down the road, he said.

"Diesel has some advantages when you're talking the next five years," Lynskey said. "You can't distribute E85 through the regular pipelines because of its corrosiveness, so at the moment we have to truck it around."

Diesel also has more consumer appeal in general, even outside the luxury brands, according to Mike Jackson, chief executive for AutoNation, the largest dealership group in the U.S. that sells vehicles from companies based in Germany, Japan, Italy and South Korea, as well as domestic brands. His broad-based exposure to basically every manufacturer has made Jackson's opinions highly sought after in the industry, where he addressed an auto analyst conference during the Detroit show's preview days.

"I think the next popular technology will be diesel" since new-generation diesels are as smooth and quiet as gasoline cars, Jackson said.

"With cleaner diesel fuel, yes, there's a price penalty (for the emissions equipment and therefore cost of the vehicle), but there's also 30 per cent more range, which is key. A lack of range is what killed the first electric car."

Other upcoming diesel vehicles scheduled to become available in 2008 include the Audi Q7 TDI, the Acura TSX and the Volkswagen Jetta sedan, with other diesel models from Honda and Mitsubishi also planned respectively for 2009 and 2010.

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