AFTER years in the automotive wilderness, largely exiled to the smoky borders of truck stops, diesel is coming home. Americans may not recognize its freshly scrubbed face.

A 19th-century invention by Rudolf Diesel, the diesel engine has always been known for outstanding fuel efficiency, with better mileage (by 25 percent to 40 percent) than gasoline. But the kerosenelike fuel and the engines that burn it were dirty, noisy, dawdling and even deadly, linked to increased risk of cancer and respiratory disease.

That has all changed, in part because of cleaner-burning fuel  its 2006 rollout had been mandated in 2000 by the Clinton administration  that has 97 percent less of the sulfur responsible for diesel engines’ sooty particulates.

The low-sulfur fuel, hailed by the Environmental Protection Agency as a historic advance, has opened the door to sophisticated emissions controls that let diesel engines meet the strict pollution standards of California. Those rules, the world’s most stringent by far, require 2009-model diesels to be as green as gasoline or even hybrid models.