Thomas Bunton didn’t start out as an advocate for diesel. It happened by accident.

Bunton, 34, went to a BMW dealership in March after being intrigued by the miles per gallon that the diesel BMW 335d allegedly delivered. After a weekend with the car, Thomas and his wife Lisa, who live in West Lafayette, Indiana, were hooked.

“The ability of that thing to run at high speeds -- at 1,600 RPMs -- while just sipping fuel was amazing,” he said, adding that his new car has doubled his miles per gallon. Lisa Bunton also switched shortly afterward to a diesel Volkswagen Toureag.

Many people assume diesels are still dirty and noisy, but he said not a single person has guessed his BMW is a diesel. “They’re just amazed,” said Bunton, adding that the shock value is exponentially higher because his car is gleaming white.

The Buntons are not alone. U.S. sales of diesel cars doubled in 2010, according to a report from The Diesel Driver. These cars aren’t your grandmother’s diesel Mercedes, either. The options on the road today are cleaner and offer more power than models of the past, and the MPG blows a gasoline car out of the water. For drivers that are looking for economic gas mileage but not ready to make the leap to plug-in hybrids or electric vehicles, diesel is growing in popularity.

J.D. Power and Associates estimates that diesel cars will triple their market share to make up about 10 percent of the market by 2015, meaning that diesel is here to stay in the U.S. (Burton’s car had to be special-ordered from the BMW manufacturing plant in Germany and delivered to the Spartanburg, S.C. plant because area BMW dealers were loathe to sell their one or two showroom models.)

“Seven years ago, diesel was a no-go in the U.S,” Peter Schwarzenbauer, a member of Audi's board, told Greentech Media last year. “But now there seems to be a trend that American consumers will embrace" diesel.

Diesel has long been a favorite in Europe, where high gas prices have created a demand for more fuel-efficient cars. Approximately 40 percent of the European car fleet is diesel, compared to just 3 percent in the U.S. But fuel economy is the number-one consideration for drivers in the U.S. these days, according to Consumer Reports, making diesels more appealing. Most diesels command a 30 percent improvement in real-world fuel economy against their non-diesel counterparts.

Just as important, these new diesels drastically cut down on the SOx and NOx emissions that were the bane of the stinkmobiles of yesteryear.

Unsurprisingly, European carmakers are leading the invasion, with BMW, Audi/Volkswagen and Mercedes Benz making up the bulk of sales. In the fourth quarter of 2010, nearly half of the Audi sales were diesel; for BMW, the figure was about a third. But American carmakers still relegate diesel to mostly trucks, although companies such as Ford have diesel cars that sell well in Europe, so they could bring them over anytime they think the market is ripe.

For the forward-thinking environmentalists, like Max Hamalainen, 24, who drives a 2005 diesel Volkswagen Jetta TDI that he purchased used in 2008, the great fuel economy and potential of biodiesel is also part of the appeal. “There could be a bright future in biofuels,” said Hamalainen. “Unlike pure electric cars or hydrogen fuel cells, biofuels seem like a more realistic alternative for future cars."

Although there are concerns over the competition between biofuels and food stock, companies like Solazyme, Joule Unlimited, and Sapphire Energy are working on producing biofuel from algae. Amyris converts plant-sourced sugars into renewable diesel fuel and renewable chemicals. A recent study found that algal fuel could replace 17 percent of U.S. fuel imports by 2020, although challenges remain to scale the technology.

Some diesel enthusiasts are finding homegrown solutions while waiting for the technological breakthrough in mass-produced biofuels. Most diesel cars can also only run on a portion of biofuels, although many do-it-yourselfers say it’s easy to convert an engine to take all biodiesel that you can source yourself. Fish Restaurant in Sausalito runs all of its trucks and vans on used oil from the restaurant’s fryer.

Some startups are also getting into diesel by looking at ways to make the engines even more efficient. Achates Power says its two-stroke opposed piston diesel engine can increase fuel efficiency by another 10 percent to 15 percent. Ecomotors also has an opposed piston engine that it claims can increase efficiency. However, there is no word yet that any major carmakers are using this technology.

For all of the love for diesels, only about half of the gas stations in the U.S. carry diesel, according to Johan de Nysschen, president of Audi America. However, many diesel cars can go more than 600 miles on a single tank, so most diesel drivers say that it’s not a constraint in the same way that the all-too-real range anxiety of driving an all-electric car may be. Bunton said that he made the initial drive from the BMW factory to downtown Washington, D.C. on less than one tank. Filling up was a problem once they got there, but only because most gas stations were closed anyway, and they easily refueled once back on the highway.

Making fewer trips to the pump isn’t just convenient for diesel drivers; it also helps to wean the U.S. off of foreign oil. If diesel penetration could reach 20 percent in the U.S., that would cut the need for about 700,000 barrels a day, according to Audi’s Schwarzenbauer -- about half of what the U.S. imports from Saudi Arabia.

Although the new model cars burn diesel cleanly, Bunton noted the pumps themselves can still be dirty. Some diesel drivers go so far as to wear gloves when they fuel up. But it’s a small price to pay for the driving experience. Although his car doesn’t coast the same way a gasoline model does, the torque at low RPMs is addictive. “I can’t see myself going back at this point,” said Bunton.

For now, American drivers that have converted are finding themselves to be diesel evangelists, even if they didn’t start out with that intention. Bunton, whose last car was a Chrysler 300C, noted that he wasn’t looking to purchase a flashy European car, but he found that American carmakers didn’t offer diesel options like they do in Europe. “It’s a great conversation piece with people,” he said. “You walk in with one idea [about diesel], and walk out saying ‘Wow, this has really changed.’”