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The Diesels Are Coming

By Carey Russ (c) 2004

In some parts of Europe, 40 percent of new cars sold are powered by diesel engines. In the United States, about 0.4 percent of cars are diesel-powered. Diesels have never been popular here, with relatively low-priced gasoline and different emissions regulations seeing to the triumph of the spark-ignition gasoline engine.

Diesels almost gained a toehold during the fuel crises of the 1970s, but the noise and soot from the injection systems of the day, and unreliability due to the hasty conversion by some manufacturers of gasoline engines to diesel killed any chance of their success at that time. A diesel can be up to 30 percent more efficient than a gasoline engine because of the greater potential energy in diesel fuel and the high compression used to ignite the fuel-air mix to extract that energy. But the stress on the engine components from that compression is much higher than the stresses in a gasoline engine, and the pistons, connecting rods, crankshaft, bearings, and engine block of a diesel must be stronger than in a gasoline engine of similar output. Convert a gas engine to diesel without proper strengthening, and you'll be guaranteed to have serious problems.

Diesels emit far less carbon dioxide and carbon monoxide than gasoline engines, but more nitrogen oxides and highly-noticeable soot and particulates. Anti-pollution techniques first used for gasoline engines are making their way to diesels, with devices similar to catalytic converters used to scrub out toxins and soot. Particulate traps can reduce soot in the exhaust by up to 90 percent; oxidation catalysts reduce nitrogen oxides in the exhaust and increase the lifespan of the particulate trap. And, as the makeup of gasoline has changed to reduce pollutants, look for diesel to change as well. The future belongs to low-sulfur diesel, which is required to make the best use of the newest and most efficient particulate traps and catalysts, much like unleaded gasoline is necessary for use of catalytic converters.

Diesels have used fuel injection since Rudolf Diesel invented the engine over 100 years ago, but until recently injection systems were mechanically-controlled. This meant that unless tolerances and construction were akin to an expensive mechanical watch mixtures could be imprecise. And, as with a gasoline engine, imprecise mixtures lead to pollutants.

Electronics to the rescue. As in gasoline engine fuel-injection systems, the newest diesels are using sophisticated electronic fuel injection. Electronic injection systems, besides being less expensive than mechanical ones, are more precise than all but the highest-quality mechanical systems, and injection timing can be changed dynamically for the best results. This metering flexibility and precision results in cleaner-running and more powerful engines. And they are also quieter.

Currently, most diesel-powered vehicles available here are trucks. Ford, Chrysler, and General Motors pickups are all available with diesels, as are the DaimlerChrysler Sprinter commercial van and Ford Excursion and Hummer H1 SUVs. Diesel passenger cars are in the minority, with versions of the Volkswagen New Beetle, Golf, and Jetta the only current offerings. But that is about to change.

Two new diesel-powered sedans are coming Stateside soon, the 2005 Mercedes-Benz E320 CDI and the 2004 Volkswagen Passat TDI. Both German manufacturers have a long history of diesel production, and their diesel products have a cult-like following in the U.S. This following could easily increase, especially with rising gasoline costs.

The Passat will have a 2.0-liter turbocharged engine with direct fuel injection, hence the (T)urbo (D)irect (I)njection moniker. With 134 horsepower at 4,000 rpm and 247 lb-ft of torque at 1,900 rpm, performance should not be a problem. Torque is what gets a vehicle moving, and diesels excel at torque production. They also excel at fuel economy, and the Passat TDI is rated at 27 mpg city / 38 mpg highway. This in a comfortable, spacious mid-sized sedan, not a tiny ``econobox.'' I had the opportunity to drive a European-spec Passat TDI recently at the ``Challenge Bibendum'' alternative-fuels event held at Northern California's Infineon (formerly Sears Point) Raceway. Although not a racetrack car, the TDI acquitted itself very well on the hilly, twisty track. It was not underpowered or slow, and made the steep climb from Turn 1 to Turn 2 with ease. It was also emphatically not noisy or sooty; it was very hard to tell that the car was not a regular Passat 1.8T. An American-spec Passat TDI is expected soon.

A bit further up the socieo-economic scale is the Mercedes-Benz E320 CDI, also soon to be available in the U.S. Mercedes has been making diesel cars since 1936, and about 40 percent of its car sales worldwide are diesel-powered. Mercedes diesels have a long-standing and near-fanatic following, and an excellent reputation for reliability and longevity. The last diesel offering here was the E300D in 1999, but 73 percent of U.S. sales were diesel in the early 1980s. Cheap gasoline and tightening emissions legislation are behind those changes, not any deficiency in power, refinement, or drivability. I have fond memories of the E300D - a luxury sedan with enough power to squeal its tires on hard acceleration and get over 30 mpg is not something to forget. The E320 CDI promises to be even better, with an EPA fuel economy rating of 27 city / 37 highway and a 0-60 time of 6.8 seconds - 0.3 seconds quicker than a gasoline-powered E320.

If these two cars are successful, expect to see more diesels. And if fuel prices continue to skyrocket, expect more people to buy diesel. Oh, yes - there is absolutely no reason that a small diesel can't be used in a hybrid vehicle, for even more impressive fuel economy. The next ten years are going to be an exciting and interesting time in the automobile industry.