By Michelle Krebs, 2/28/2002

In recent weeks, an official from the US Environmental Protection Agency claimed publicly that, despite arguments by automakers to the contrary, tougher emissions rules wouldn't be a barrier to modern diesel engines. DaimlerChrysler recently said it would soon decide whether to test-market a diesel-powered Jeep Liberty.

Automakers generally have been anxious to reintroduce diesels in the United States to boost fuel economy and reduce certain kinds of emissions. In light of strong sales of the Volkswagen Golf TDI and General Motors's new diesel-powered heavy-duty pickup trucks, at least some consumers appear to be ready for diesels.

The Golf TDI, the only diesel-powered car sold in the United States, has continually increasing sales. Since General Motors introduced its heavy-duty Chevrolet and GMC trucks with a Duramax diesel engine, waiting lists have been as long as six months. The automaker is adding factory capacity to increase production of diesel engines by 50 percent.

Though diesel engines have been around since the dawn of the automotive age, only 3 percent of vehicles sold in North America are powered by diesel engines. In Europe, 35 percent of vehicles are diesel powered, and industry specialists predict that percentage will rise to 50 percent, as it already has with some individual automakers. Those same specialists hesitantly estimate North American diesel sales might hit 10 percent by 2010, at best. The EPA official, more optimistic, predicted a rise to 20 percent of the US market by the end of the decade.

Indeed, diesel technology has come a long way in the past decade. The diesel-powered Liberty sold in Europe, the Golf TDI, and GM's diesel-powered pickups that I recently test-drove clearly demonstrated how far they'd come since the noisy, small Volkswagen Rabbit I drove in the 1980s. And anyone who has rented a diesel-powered BMW 7 Series, Audi A8, or a Mercedes-Benz S-Class in Europe likely could tell no difference until filling the fuel tank.

Diesel engines are attractive for their fuel economy. Today's diesels deliver up to 30 percent better fuel economy than do gasoline engines. Diesel fuel has a higher energy density than gasoline: One gallon of diesel fuel produces more energy than a gallon of gasoline. A diesel engine also uses higher compression ratios than does a gasoline engine, which burns the fuel more efficiently. Higher fuel economy results in reductions in some emissions.

In Europe, diesel engines have been popular not only for their high fuel economy in an area where gasoline prices are sky high, but also because they have lower greenhouse emissions, particularly carbon dioxide, that is believed to contribute to global warming. In addition to fuel economy and emissions advantages, the new diesels are enjoyable to drive. They are no longer noisy, smelly, and slow.

The newest diesel engines have benefited from technologies such as turbochargers and multiple valves that were developed for gasoline engines. New ways to inject fuel into the combustion chamber of diesel engines are improving fuel economy and emissions as well.

Major breakthroughs have also advanced today's diesel engines. The most significant breakthrough is Common Rail fuel systems, which store fuel under high pressure to improve fuel economy and reduce noise and emissions. Automotive experts call the shift to common rail for diesels as important as the shift from carburetors to electronic fuel injection in gasoline-powered vehicles.

In the United States diesel engines still face challenges in meeting emissions regulations. While they emit lower levels of carbon dioxide, they spew higher levels of oxides of nitrogen emissions - believed by some experts to be carcinogenic - and particulates or soot, which creates smog. Automotive specialists say today's diesel engines cannot meet upcoming US and California emissions regulations. Recent suggestions by government officials, however, suggest there may be room for negotiating some flexibility so that automakers can sell diesels. And automakers and their suppliers are continuing to work on diesels to try to meet the new laws.

Beyond the technical challenges, the business case for diesel-powered vehicles is a stumbling block for Americans. Diesel fuel is not readily available at all service stations, and it is more expensive than gasoline, giving Americans little incentive to purchase a diesel vehicle.

The business and political challenge is bigger than the technical challenge, say automotive diesel engine specialists who are feverishly working on the technical challenges.

This story ran on page G7 of the Boston Globe on 2/28/2002.
© Copyright 2002 Globe Newspaper Company.