HERNDON, VA - Diesel engines have long gotten a bad rap in the U.S., but that's a tired story. We all know it, some of us even believe it, but so far not much of the U.S. populace has been exposed to a proper modern diesel engine in a passenger car. That's no fault of Audi's, though, as they've been at it for 20 years now, and they're one of the few carmakers in the U.S. offering diesels in a luxury vehicle--and luxury cars are arguably the platform best suited to changing hearts and minds. It's also worth wondering where it's all going over the next 20 years as diesel ramps back up in the U.S.

Mercedes-Benz offered diesels for a long time, and has recently returned to the field in the U.S. with the ML350, R350 and GL350 BlueTec vehicles. An E250 BlueTec E-Class sedan is also expected next year. That puts them in the lead among luxury carmakers in the U.S. Even BMW has a plan to bring four-cylinder diesels to complement its 335d and X5 xDrive35d models currently on sale.

Audi is close behind, however, with the A3 TDI and Q7 TDI already on the market. Despite their short-lived patch of recent history in the U.S., Audi has 20 years of experience building turbodiesels around the world, starting in 1989 with the Audi 100 2.5 TDI, the first Audi with a turbocharged, direct-injection diesel engine.

Since that first car, over 5 million Audis have been born as TDIs, the powerplant evolving through several iterations along the way. First was a five-cylinder 120-horsepower/195-pound-feet 2.4-liter engine, later upgraded to 140 horsepower and 214 pound-feet of torque. The Audi 80's little 1.9-liter diesel was rated at just 90 horsepower but 134 pound-feet of torque, upgraded in 1995 to 110 horsepower thanks to a new turbo with Variable Turbine Geometry (VTG) to help improve low-speed boost.