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Audi's TDI Offensive

Its new 3.0-liter V6 diesel meets the toughest emission standards and is the first of what could be many diesel offerings to come from the German automaker.
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Giovanni Pamio is a powertrain development engineer at Audi. He is also one of the founding fathers of common-rail diesel design, having worked at Fiat on its JTD (uniJet Turbo Diesel) engine. "That project started in 1983 with a single-cylinder motor that had an injection pressure of 1,200 bar (17,400 psi)," he says. Today common-rail engines use 2,000-bar (29,000 psi) piezo injectors to give five injections per cycle to reduce noise, particulate emissions, and improve efficiency, but still build on the technology first seen in 1983. "Common-rail technology has made it possible to create diesels much cleaner than anyone would ever have thought possible only a few years ago," he says. In combination with turbocharging-"an absolute necessity to get the greatest power and efficiency from a diesel motor," says Pamio-urea injection, particulate filters, DeNOx converters, and low-sulfur fuel, Audi's common rail 3.0-liter V6 TDI engine meets 50-state LEV II Bin 5 emission standards. This, Audi claims, makes it the world's cleanest diesel engine.

"Between 1990 and 2007," says Pamio, "specific output of our TDI engines has risen more than 100%, torque output has risen more than 70%, particulates have declined by 98%, and HC and NOx have fallen 95%." Still, to reach the emission levels outlined in the EPA's LEV II Bin 5 regulations-the toughest diesel regulations in the world-more had to be done. In particular, it required the combination of a diesel oxidation catalyst, diesel particulate filter, and the addition of a urea metering unit upstream of the DeNOx converter. The 32.5% urea solution reduces NOx emissions by as much as 90% by breaking down into ammonia in the hot exhaust and splitting the nitrous oxide into nitrogen and hydrogen. Though the urea filler is located under the fuel door, Audi says customers won't have to worry about refilling the tank as even the most aggressive driver won't empty the tank between dealer service appointments.

The 3.0-liter V6 uses four valves per cylinder, has a 90? bank angle, 90-mm between bore centers, and has a block made from vermicular graphite cast iron, which is 15% lighter than conventional cast iron, giving the 17.3-in. long engine a dressed weight of 498.2 lb. Camshafts and ancillaries are driven via chains located on the back of the engine, a design similar to Audi's 4.2-liter V8 on which this engine is based, and one that allows for a lower hoodline without reducing the space needed to meet Europe's tough pedestrian crash standards. "The glowplugs don't require the driver to wait before he starts the car," says Pamio. Unlike past design, these new plugs can reach more than 1,800?F within two seconds. In addition, the engine is fitted with pressure sensors that help the engine compensate for the regional difference in cetane ratings found in U.S. diesel fuel. "The average cetane rating in Europe is between 51 and 54," says Pamio, "while the regional differences in the U.S. are such that this number varies anywhere from 39 to 54." However, the technology guarantees that the engine produces its full 221 hp and 406 lb-ft of torque no matter where it is refueled.

The 3.0 TDI diesel will launch late this year in the 2009 Q7 SUV and A4, but Audi is watching how the market reacts before deciding to expand its diesel offerings. Says Pamio: "There's nothing-technically speaking-that prevents us from bringing our other diesels into the U.S. when demand reaches a level that will support their introduction." 

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