2009 Volkswagen Jetta TDI (© Volkswagen AG)Click to enlarge picture

Volkswagen will offer the Jetta TDI (shown here) and the Jetta SportWagen TDI with its new 50-state legal, 2.0-liter turbocharged diesel. Both models have an EPA combined mileage rating of 33 mpg — 43 percent better than the same vehicle powered by a 2.5-liter gasoline engine.

An old solution to high fuel prices is new again, as American drivers get ready to take a fresh look at diesel-powered automobiles. With the conversion of the diesel motor-fuel supply to a new, low-sulfur formula all but complete, auto builders are preparing to roll out the next generation of diesel-powered cars and SUVs that are 98 percent cleaner than diesels sold just two years ago. They also offer 23 to 43 percent better fuel economy than the same vehicle with a gasoline engine, efficiency that comes close to matching that of gas-electric hybrids. The final bonus is a $1,300 federal income-tax credit available to buyers of eligible diesel-powered vehicles to offset the higher price of the diesel engine.

Volkswagen and Mercedes-Benz started selling vehicles with the new 50-state-certified, low-emissions diesel technology in October. Audi, BMW, Cadillac and Honda have diesel-powered cars scheduled to debut in the next year, while Ford has plans to offer a low-emissions diesel F-150 pickup in 2009. Each of these vehicles meets new Environmental Protection Agency emissions standards for diesels, a feat made possible by the application of new technology and the introduction of ultra-low sulfur diesel fuel (ULSD). The new fuel has sulfur concentrations of no more than 15 parts per million, 97 percent less sulfur than was allowed in diesel fuel sold before 2006.

Like the switch to unleaded gasoline in the 1970s, ULSD enabled the development of exhaust-scrubbing technology that could not cope with previous high levels of sulfur. Though they vary in detail, most will utilize a three-stage system similar to that deployed by Mercedes to detox the exhaust: a catalyst that minimizes hydrocarbons and carbon monoxide; a self-cleaning filter that traps and stores soot; and a device that delivers a liquid urea solution, known as AdBlue, to the exhaust. Through a chemical reaction, the AdBlue converts nitrogen oxides (the culprit behind acid rain) into harmless nitrogen and water vapor. The AdBlue reservoir will be refilled at the time of an oil change, typically each 10,000 miles. The new Volkswagen TDI models are small and light enough not to require the AdBlue component. Honda, meanwhile, has developed a two-stage exhaust system for a forthcoming Acura model powered by its i-DTEC diesel that also will not require the AdBlue component.

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Diesel powers more than 50 percent of autos in Europe, where tax incentives keep prices for diesel fuel significantly lower than for gasoline. But drivers who were around for America's previous infatuation with "oil burners," which followed the twin oil-price spikes of the 1970s, might cringe as they recall the noisy, under-powered engines, sooty exhaust and cold-weather foibles that came with cars like the 50-mpg diesel-powered Volkswagen Rabbit, introduced in 1977 — not to mention haunting grubby truck stops for fuel. Today, low-sulfur diesel is widely available across the country at neighborhood filling stations, and the diesel engines debuting for 2009 display little diesel-engine clatter, are surprisingly powerful and emit none of the characteristic diesel smell associated with a city bus.

"We took a test drive in the new Volkswagen Jetta TDI, and when we got back to the dealership, the salesman wiped the tip of the exhaust pipe with the cuff of his white dress shirt," said Bob Mueller of Milwaukee, who encouraged his daughter to buy the new diesel-powered 2009 model. "It was absolutely clean."

Mueller, a 65-year-old retired machinist, averages about 40 mpg with his 2004 Jetta TDI.

"I just drove from Maryland to Wisconsin on a tank and a quarter of fuel," said Mueller. "The new Jetta is cleaner and quieter than my car and delivers great performance."