Time to Step on the Diesel

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By Warren Brown
Sunday, October 22, 2006

We were averaging 31 miles per gallon, which would not have been spectacular in a four-cylinder economy car. But this was a 2007 Mercedes-Benz ML320 CDI -- a luxury midsize, all-wheel-drive, V-6 diesel sport-utility vehicle capable of pulling a trailer weighing 5,000 pounds and carrying 1,400 pounds of cargo.

The "CDI" in its name stands for "common rail direct injection," an advanced diesel technology used for nearly a decade in many European countries.

The technology is becoming more popular in Japan. And thanks to newly implemented federal rules requiring the sale of cleaner diesel fuel, CDI diesel vehicles and their equivalents soon will be traveling highways in the United States.

This is a good thing for energy conservation, clean air, the automobile industry and consumer choice.

CDI diesels require low-sulfur diesel fuel, the kind that began flowing to fuel stations in most parts of America on Oct. 15, the day the new federal regulations took effect.

According to the Diesel Technology Forum, an information clearinghouse for the nation's diesel industry, low-sulfur diesel is 97 percent cleaner than the predecessor formulations of diesel fuel that, when burned in traditional compression-ignition diesel engines, produced the smoky, particulate pollution blamed for causing lung cancer, asthma and other respiratory illnesses.

Low-sulfur diesel reduces those risks. And low-sulfur diesel burned in modern common rail direct injection engines helps to reduce those risks even more.

The diesel engine, developed by German engineer Rudolf Diesel in 1892, compresses the air-fuel mixture in combustion chambers until it becomes super-heated and ignites, thus producing the power to move drive shafts and wheels.

Diesel engines use no outside ignition device, such as a spark plug.

In traditional diesel engines, a piston pushes air to the top of the combustion chamber, compressing and heating it to the point where it can then receive and ignite an injection of diesel fuel.

Common rail direct injection diesels constitute a major development in compression-ignition technology. A high-pressure pump stores a reservoir of fuel in a tube -- the "common rail" -- that branches off into computer-controlled injection valves. The fuel is precisely metered, meaning that it is delivered at the optimum combustion point for a cleaner, more complete, more powerful burn.

High-sulfur diesel fuel undermines the performance of exhaust-control devices on diesel engines "the way lead once impeded the effectiveness of catalytic converters in gasoline cars," according to the Diesel Technology Forum. "Removing the sulfur from diesel will usher in a new generation of clean diesel technology applications across all vehicle types," the forum predicts.

There is reason to believe.

Sales of diesel-powered passenger vehicles in Western Europe, where there are heavy taxes on gasoline, account for nearly 50 percent of all new cars and trucks sold in that region. It is policy with a purpose.

The European reasoning is that diesel-powered vehicles are from 20 to 40 percent more fuel-efficient than their gasoline-powered counterparts. Placing onerous taxes on gasoline to shift consumer buying habits to diesel is seen in Europe as an effective energy conservation policy, especially now that low-sulfur diesel and common rail direct injection engines have rendered diesel a less onerous environmental burden.

But skepticism remains in the United States, where diesel models account for only 3.2 percent of the market and where vehicles such as the Mercedes-Benz ML320 CDI remain barred from sale in California, Maine, Massachusetts, New York and Vermont -- states that have imposed stringent emissions-control regulations.

But even more advanced diesel engines are on the way from foreign and domestic car companies. Technology will team with political clout, the latter wielded by powerful automobile dealer groups in those states that now bar diesel sales, to make passenger diesel cars and trucks available everywhere in America. It's just a matter of time; and time, in this case, is on diesel's side.


© 2006 The Washington Post Company

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