Audi's 40+ MPG Clean Diesel Sports Cars

A while back, Alfa Romeo announced it would offer diesel engines in its Spider roadsters. Now, Audi will offer TDI diesel engines in its new Audi TT 2.0 TDI Coupe quattro and Audi TT Roadster 2.0 TDI quattro. As might be expected, fuel economy is impressive at 44 mpg for the coupe and 42 mpg for the roadster. Impressive, too, is that these 3000+ pound high performing sports cars have a 140 mph top speed and 0 to 60 mph times of around 7.5 seconds.

The new four-cylinder TDI (turbo direct injection) engine is the latest version of the most-produced diesel engine in the world. The 1988 cc produces 170 horsepower at 4250 rpm and 258 lbs-ft of torque over 1750 to 2500 rpm. Both versions are fitted with a manual six-speed transmission and Audi's quattro permanent all-wheel drive.

Improvements include new common rail injection with eight-hole injection nozzles that can perform up to five distinct injection sequences per cycle. This fine degree of modulation creates a modest pressure increase in the combustion chambers, resulting in a significantly reduced noise. A pressure of 26,500 psi allows fuel to form a fine dispersion for precise, highly efficient combustion.

A new adjustable vane turbocharger allows rapid torque buildup to eliminate turbo lag. The positions of swirl flaps on the intake manifold are controlled by electric motors so they adapt the flow of air to the current load and engine speed. Piston geometry has been modified and camshaft drive belt acoustics have been refined.

The engine has a 5000 rpm redline, high for a diesel. Improved combustion chamber thermodynamics means the engine can run on up to 60 percent recycled exhaust that has been thoroughly cooled by the radiator to reduce untreated NOx emissions. The 2.0 TDI already meets Euro 5 emissions requirements.