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Audi's parent company Volkswagen already produces some of the cleanest-burning, most fuel-miserly diesel engines in the world. The Jetta TDI was recently released in the U.S. and has been making waves for its hybrid-like efficiency. So it's natural that Audi would want to show off its green credentials with a new diesel sedan of its own, and it has done so with the A4 TDI concept e, introduced at the Paris Motor Show. Based on the brand-new A4 platform, the new concept gets a 2.0L four-cylinder common-rail direct-inject turbodiesel derived from the unit powering the Jetta TDI. That mill sees tweaks to its valvetrain and cooling systems, lowering its power output a bit to 120-horsepower and 214 lb-ft of torque, but increasing its fuel efficiency a great deal.

Added to the powertrain is a start/stop system that keeps the engine from idling when not needed and regenerative braking, which charges a secondary battery that keeps all your goodies running while the engine's off. The engine has also had its efficiency-robbing power steering pump removed and the rear brakes are now electrically actuated as well. All of this, plus many other small details, adds up to a remarkable 59 miles per U.S. gallon in EU combined testing! Its 10.5 second run to 60 won't win any drag races, but considering the cost of fuel and pending eco-legislation in the world's largest markets, we'd imagine that the technologies on this car will go from concept to production in short order.

[Source: Audi]