Diesel. Strangely enough, it means clean.

General Motors today formally announced it will come out with a version of the gas-sipping Chevy Cruze with a diesel engine in 2013. Modern diesels can get 20 percent to 40 percent better gas mileage than their gas counterparts. The current "eco" version of the Cruze gets 28 miles per gallon on the street and 42 mpg on the freeway, while the more standard version clocks in at 26/36 mpg. At the high end of things, this would give a diesel Cruze a mileage of 50 to 58 mpg on the highway and 35 mpg in the city.

Such a car would best the Toyota Prius (50 mpg) in mileage, although it would not top the coming plug-in Prius. But, unlike a hybrid, a diesel car would likely have pretty tremendous acceleration. Diesels can also go 600 miles on a single tank, much farther than plug-in hybrids or electrics. (That's a generic shot of the Cruze above.)

Who knows? The Cruze could even encourage Ford to bring the touted, high-mileage diesel Focus made for the European market to the U.S. Volvo also has a hybrid diesel on the way.

Diesel is enjoying a second life in the U.S. Although a mainstay in trucking and trains, diesel cars faded out in the U.S. because of emissions issues. Although they get better mileage, diesel engines in general emit more particulate matter -- NOx and SOx -- than gas cars. Improvements in the technology and a proliferation of diesel pumps, however, has helped boost their popularity.

Volkswagen sold out of Audi and Volks diesels in 2009 and saw a similar surge in 2010.

“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.

JD Power and Associates estimates that diesel cars will triple their market share, surging to about 10 percent of the market by 2015.

Several companies such as Solazyme also hope to increase the flow of biodiesel to fuel pumps, further cleaning diesels.

Further out, expect to see trucks and/or cars powered by opposed piston diesel engines from the likes of Achates Power and EcoMotors. Achates Power says its two-stroke opposed piston diesel engine can increase fuel efficiency by another 10 percent to 15 percent.