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One easy way to reduce both carbon-dioxide emissions and oil imports is to switch to diesel engines in cars and trucks, since they’re inherently more efficient than gasoline engines. In fact, diesel engines are almost as efficient as gas-electric hybrids, without the need for hybrid technology.

But to date, consumer diesel vehicles have not been widespread in the United States, where tight emissions controls made them more expensive to develop than in diesel-loving Europe. What’s more, U.S. drivers’ historical indifference to fuel economy–along with their perception that diesel engines are smelly and dirty–convinced automakers that Americans wouldn’t buy them anyway.

Starting on October 15, however, ultra-low-sulfur diesel will be available throughout the United States at the pump, as a result of EPA regulations originally devised by the Clinton administration.

By itself, the new diesel fuel will cut soot emissions by 10 percent–but it also opens the way for affordable technologies that can reduce emissions by 90 to 95 percent. The reason sulfur is so significant is that it forms organic sulfates, which create soot, clog emissions filters, and render ineffective catalysts that help convert the soot to harmless materials.

The new U.S. fuel standards slash sulfur levels in diesel from 500 parts per million to 15, making practical the kinds of emissions controls already used in Europe, as well as better treatments for nitrogen oxides, which are key components in smog. This improvement should make meeting toughening emissions standards far easier–and could pave the way for a new diesel era in the United States.

“The cleaner diesel fuel opens the door to diesel cars that can be as clean as gasoline cars, yet offer 20 to 40 percent better fuel economy,” says Richard Kassel, senior attorney at the National Resources Defense Council. Such efficiency gains approach those of gasoline-electric hybrid vehicles and, as with hybrids, the clean diesel vehicles would also cut carbon-dioxide emissions by reducing the total fuel consumed.

While a few diesel cars have been available in the United States, more automakers are poised to enter the market. Allen Schaeffer, executive director of Diesel Technology Forum, a not-for-profit educational group representing diesel equipment manufacturers, says Honda will have a diesel vehicle (probably an Accord) for the United States in three years. GM has announced a light-truck engine for 2010, as has Cummins. Meanwhile, Daimler-Chrysler is introducing a Mercedes diesel vehicle into the United States next week, and a new Jeep Grand Cherokee next year. Volkswagen also has several diesel vehicles on the market, he says.

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