There are even those who believe the diesel engine is finally ready to win the hearts of U.S. passenger car buyers, much the way it has in other countries. To do that, diesel advocates acknowledge that manufacturers need to woo customers and try to erase the memory of previous disasters, such as the General Motors sedans of the 1980s.Further clouding the future are issues such as availability of diesel fuel at urban and suburban gas stations, as well as the price of a gallon of diesel, which now routinely costs a few pennies more than regular grade gasoline.

Nonetheless, today's passenger car diesel is a strong product, offering unprecedented performance along with economy of as much as 49 miles per gallon, primarily due to two technologies introduced in the last 10 years: direct fuel injection and common rail fuel delivery. Electronic diesel injection controllers vary the pressure and amount of fuel spray during combustion. A three-stage sequence insures a cleaner burn. Common rail is a little simpler. The "rail" is a manifold in which extra pressure helps vaporize the fuel for a better burn. The intense pressure also makes more accurate timing possible.

These technologies are already found in the latest generation of domestic pickup trucks -- like the Ford Power Stroke and GM/Isuzu Duramax -- but the systems are more finely tuned for passenger car diesels.

This year the only passenger car new diesel you can drive is at Volkswagen, and it's called a TDI: Turbo Direct Injection. It's a turbocharged, 90-horsepower, 1.9-liter inline four-cylinder, and you can get it in the Golf two-door or four-door liftback, the Jetta four-door sedan or station wagon, or the retro-style New Beetle. You will have to drive a TDI to experience it. It is different. You will hear some diesel noise when you start it, but you won't have to wait for glow plugs to warm up. You won't smell diesel fuel, and there won't be any black smoke. The "knock" sound of the old diesel is virtually eliminated. Although a TDI will be noisier than a gasoline engine idling at an intersection, it gets quieter as it revs higher.

Most TDI's are sold with automatic transmissions, and the automatic is programmed to make the most of the torque rather than the speed of the engine. Pulling away, the sound drops to what you might expect from a gas engine at full throttle. In fact, the harder you urge it on, the more the TDI resembles a gasoline vehicle.

Let it loaf, and it shows its diesel side. And it likes to loaf. The other time this engine is subdued is when it reaches highway speeds, where the "gray noise" of wind and road hide the engine sound almost entirely. A diesel turns a lot slower at cruising speed than a gas engine. You can relax and enjoy the power and the mileage, just like the big rigs.

You may even decide the new diesel is more fun to drive. Diesel has its enthusiasts, many of whom have recently been won over to the new technologies. New diesels are already rolling out in Europe, where about 35 percent of the passenger vehicles are diesel. That's expected to increase to 50 percent by 2010.

Mercedes is not selling passenger diesels in the U.S. currently but in Europe offers a 200 and 220 four- cylinder, a 270 five-cylinder, a 320 six-cylinder and a 400 V8. All are labeled "CDI," denoting common rail with direct injection. The 413 pound-feet of torque in the Mercedes diesel V8 can push a 4,200-pound S400 sedan to over 60 mph in about 7 seconds. Government regulations will play a large role in the possibilities for development of diesel in the U.S. The U.S. Department of Energy favors diesel because it diversifies fuel use and because bio-diesel fuel can be easily synthesized from domestic agriculture.

One hurdle is proposed U.S. Environmental Protection Agency rules that would limit particulate emissions -- long a problem with diesels. The U.S. rules differ from European environmental regulations, which focus on greenhouse-gas reduction and promoting low-sulfur fuel. The higher efficiency technologies of the new generation of diesel engines can pay off in overall environmental cleanliness, but a quantum leap will have to be made to clear EPA particulate regulations planned for 2007.

What may ease the problem is unprecedented action by several oil companies to participate in diesel fuel environmental solutions. BP is among the refiners who support the proposed EPA regulations. BP also recently completed a three-year test that made low-sulfur diesel available in the U.S. for extensive fleet testing. Diamond Shamrock blended a new diesel fuel for Texas, one that they say would meet stricter California emissions standards.

Waiting in the wings are other new diesel technologies involving cleaner fuels going in and ways to scrub the exhaust coming out. There also are high-tech solutions for particulates -- new catalytic mufflers that trap and burn the particles to ash. The 30 percent better combustion efficiency of the compression ignition engine can't be denied. That basic engineering advantage supports investments by the multi-national automobile manufacturers. With the success of the technologies in Europe, it's only a matter of time before these products migrate to the United States.

And what about Asian manufacturers? Last year, Volkswagen was the only manufacturer to offer a passenger-car diesel in the U.S. But some of the more popular vehicles may soon have a diesel option. Isuzu, which makes the full-sized truck diesels for GM, has announced a program of smaller 3-liter four-cylinder diesels that will be built in Indiana for the Rodeo and Axiom sport-utility vehicles.

Says Chuck Letavick of BP: "The industry has to overcome the public perception of 'old diesel' as 'not-too-good'."

The current Volkswagen ad for the TDI doesn't even use the word "diesel" anywhere. Says Tony Fouladpour, VW public Relations Manager: "We have the traditional diesel enthusiasts. The strategy of the ad is to introduce the technology to new customers."