Dr. Rudolph Diesel's invention of the oil-burning diesel engine was a major advance in mechanical technology, but the motor never has had widespread acceptance on the American automobile market.

Volkswagen AG, however, is so convinced of the diesel's merits that it continues to press on with its development. In pursuing the technology of using compression instead of a spark plug to ignite the fuel, Volkswagen has created its newest masterpiece, the 1.6-liter ECOdiesel.

As a diesel engine to end all diesels, this motor takes a quantum leap forward in minimizing the diesel's effect on the environment. Exhaust pollutants, noise and soot, and unpleasant exhaust odor are reduced.

The engine has been installed in a new VW offering, the 1991 Jetta GL ECOdiesel that takes the place of the Jetta GL Diesel.

"We've only had the car for two weeks," said Rick Shewmake, general sales manager for Speedway Volkswagen, "so our diesel customers are just beginning to come in and look at it. To date at least, their reactions have been pretty favorable.

It's no particular secret that earlier versions of the oil burner offered by both import and domestic car manufacturers were not greeted with open arms. It was noisy. It smelled. And for a motoring public accustomed to stepping on the gas and zooming away, the diesel wouldn't get out of its own tracks.

Fuel mileage exceptional

On the plus side, the fuel mileage was phenomenal, and it ran forever if given manufacturer's recommended service. There is a contingent of owners who don't want anything but a diesel.

"Diesels have been kind of a steady sister," said Clint Kuhn, vice president and general manager of Giganti Volkswagen. "It's not the largest market, but there are people out there who are very attached to the diesel. And those seem to be mostly in the rural areas."

The new Jetta ECOdiesel has been designed to rectify past deficiencies, and to retain the advantages of mileage and longevity. Documenting the longevity factor remains in the future, but the mileage already has been rated.

VW says it's new ECOdiesel is good for 37 miles per gallon in the city cycle and 40 mpg on the highway. Mileage such as this is the province of gasoline-powered minicars, rather than an automobile the size of the Jetta.

In creating the ECOdiesel, Volkswagen worked with its proven four-cylinder diesel engine. VW engineers fitted a specially adapted low-boost (low-intake manifold pressure) turbocharger and an oxidation catalyst to the engine. They then turned the turbo away from its traditional function of simply producing more power.

Turbo acts like air pump

The turbo operates more like an air pump to improve combustion efficiency, pumping 40 percent more air into the engine's cylinders. This enables the diesel to run at full load with exceptionally low levels of carbon particulates.

The oxidation catalyst eliminates more than half of the aromatic hydrocarbons that are responsible for the char acteristic diesel smell. The catalyst reduces carbon monoxide emissions by more than 30 percent from a normally aspirated (non-turbocharged) diesel engine. Hydrocarbon compounds are reduced by more than 20 percent.

"I think there always has been some discomfort with the noise level," Kuhn said. "And there are those people who are not overly fond of the odor that comes out. But with the noise and odor being reduced, and the turbo improving performance, I think it can be a very viable alternative to a gas engine."

While emissions, noise and smell have been reduced, there has been a 13 percent increase in power.

Power increased

"They've upped the power to 59 horsepower," Shewmake said. "The old diesel was 52 horsepower. So it's going to help the performance without affecting the durability. Two hundred thousand to 250,000 miles is not uncommon with these diesels."

Fifty-nine horsepower, of course, is not going to bring home any drag race trophies, with Volksw agen rating the ECOdiesel's time for 0-60 miles per hour at 15.5 seconds. The top speed is 92 mph.

A fully equipped Jetta GL ECOdiesel carries a suggested manufacturer's base price of $11,230, and that makes it the least expensive diesel model available in the United States.

The local market for diesel-powered VWs is expected to be between 5 percent and 10 percent of a dealership's sales. However, if proposed congressional legislation imposing higher taxes on gasoline and requiring dramatic increases in fuel mileage is implemented, it virtually is certain that diesel power is going to get another look.

"I would think it would," Kuhn said. "I don't know what the percentage of sales are in Europe where gas is more expensive. But I'd think a rise in (fuel) costs would increase interest in a diesel."