Hello, Clean Diesel; Good-bye Soot

These days gasoline-electric hybrids get the applause, while older technologies get no respect. But in the United States a quiet revolution in fuel technology has been occurring, largely unnoticed. It is the mid-October shift to low-sulfur diesel fuel, a shift that will make the epitome of "clean diesel" technology available to American car buyers, including, with luck, those who reside in the "green" states that follow the lead of the California Air Resources Board.

The promise of excellent fuel economy from diesel engines is one of the great, if largely unreported, facts demonstrated by ongoing government and automaker research. When one looks at the nation's fuel economy champs as identified by the Environmental Protection Agency, several hybrids lead the pack but closely bunched right behind are diesel-powered models.

The Diesel Technology Forum claims diesels can reduce fuel consumption by 30 to 60 percent in some automotive models, obviously a giant reduction that has to be examined yet again in this age of onerous fuel prices. Further, those kinds of reductions can be accomplished with environmentally clean engines fitted with advanced exhaust emissions controls and after-treatment technology. That point of view was recently reinforced by a study done by the National Academy of Sciences.

The new low-sulfur diesel fuel is designed to facilitate the new pollution-abating technology. It contains just three percent of the pollution-generating and particulate filter-clogging sulfur that was in the previous blend sold in the United States. (Europe has been running on low-sulfur diesel for some years now.) The fuel mixture has two key benefits. It severely limits the amount of sulfur expelled into the air from diesel engines, and that alone is a huge advantage because high concentrations of sulfur are nasty. But even more important, it will open the way to a spread of clean diesel technology in America's cars and trucks, progress that was previously blocked by the previous fuel's sulfur content.

While the combustion within a diesel engine might never be as quite as clean as that in an internal combustion engine burning compressed natural gas or even gasoline, catalysts and filters can make the exhaust emissions virtually as pure. The keys to clean diesel's low emissions are in both the combustion process itself, which can be made more precise and complete using computerized controls and sensors, and in the treatment and capture of exhaust emissions after the combustion process.

In the wake of the introduction of low-sulfur diesel fuel, the difference in U.S. air quality and reliance on foreign fuels should be substantial. If the buying public is willing to give this new round of diesels a try, that is. Diesels of the past were not pretty. In 1995, gasoline-powered cars outnumbered diesel-powered trucks and buses by 28 to one, yet diesel vehicles emitted 43 percent of the smog-forming nitrogen oxides and more than two-thirds of the soot particles that went into our air. Largely because of that, Americans have never embraced diesel-powered cars and light trucks with the exception of some diesel pickup truck loyalists. While the move to low-sulfur diesel fuel will have its most immediate effects by helping clean up the pollution emitted by big trucks and buses, it is also expected to result in a substantial increase in high-fuel-mileage diesel cars and SUVs.

Driving Today Contributing Editor Tom Ripley studies the auto industry and the human condition from his home in Villeperce, France.