Audi announced a 4,800-mile American driving tour, known as the Audi Mileage Marathon, yesterday in an effort to promote the arrival of the carmaker’s TDI (turbocharged direct injection) clean-diesel technology in the US. This advanced powertrain, which will be in direct competition with Mercedes Benz’s Bluetec system, will be introduced early next year in the 2009 Audi Q7 3.0 TDI. The purpose of the cross-country journey is to showcase Audi’s ability to combine superior performance, vehicle dynamics, and high fuel efficiency.

With the cost of diesel fuel running $0.40 to $0.50 higher than regular gasoline, it’s uncertain if American consumers will adopt clean diesel technology—even if diesel’s stigma as dirty and loud can be shed.

The Audi event, from October 5 to October 20, will involve 184 international journalists in 23 TDI-equipped automobiles driving from New York To Los Angeles. The tour is designed to take these vehicles through a broad range of driving conditions, from interstates to two-lane roads, suburban traffic to city streets. “Think of it as the ultimate efficiency test,” said Marcel Barro, an automotive journalist and Marathon participant. He told Hybridcars.com, “It’s the most balanced measure of mileage I’ve ever heard of.” The Marathon will pass through a number of major cities, including Chicago, Dallas and Las Vegas, as well as famous points of interest, including the Badlands National Park, the Grand Canyon and Death Valley, Calif.

Aside from the US-bound Q7 TDI, the Marathon will involve three other Euro-spec TDI vehicles including the A4 sedan, the Q5 crossover, and the A3 three-door hatchback.

The new TDI powertrain, to be launched in the US and Europe in 2009, is an ultra low emission system that reduces oxides of nitrogen by up to 90 percent. This is possible because the system uses a fuel injector that sprays atomized fuel directly into the main combustion chamber of each cylinder, rather than the pre-combustion chamber found in older diesels. Audi’s TDIs will be compliant with California’s Tier 2, Bin 5 emission standard. It also already exceeds the requirements of the stringent Euro 6 standards that have been set for 2014.

Audi is obviously intending to promote its new lineup of diesel vehicles—however, the mileage event is likely to raise awareness of all players in the clean diesel market, most notably Mercedes and Volkswagen.