Audi Mileage Marathon runs on diesel

  • 24-Nov-2008 09:16 EST
complete V6 TDI with intercooler.jpg
A new 3.0-L V6 TDI with intercooler will be available on the new Audi Q7.

Clean-diesel engine technology powered 23 Audi vehicles from New York to California as journalists participated in a performance and fuel economy-focused marathon covering more than 4800 mi (7700 km).

"The message we take out of this event is how the cars are driven in the U.S.," Heinz Hollerweger, General Manager for Total Vehicle Development for Audi AG, said of the cross-country trek involving four Audi models (Q7, Q5, A4, and A3). The low-to-high average mpg tallies varied for the 23 vehicles fitted with Michelin Green X energy-saving tires. For instance, among the event's seven Q7 vehicles, the lowest average mpg number from Denver, CO, to Las Vegas, NV, was 25.5, while the highest for that same stretch was 29.5. The mpg difference depended "on how the car was driven," Hollerweger said.

Each vehicle's speed, distance traveled, and fuel consumption were recorded via an onboard computer. Officials from the International Motor Sports Association (the organization that overseas the American Le Mans Series) supervised and sanctioned the event. IMSA representatives were in charge of refueling all 23 vehicles at designed Shell stations along the route. To prevent unauthorized fuel stops, each vehicle's fuel tank door was sealed shut with a signed decal.

Spanning two weeks in October, the Audi Mileage Marathon served as the U.S. introduction event for the TDI (Turbo Direct Injection) engine with an ultra-low-emissions system. The Q7 will be the first Audi vehicle in the U.S. to offer the clean diesel 3.0-L V6 TDI.

"To meet the emissions standards for model year 2009, new technology was required," said Guenter Schiele, Manager of Diesel Engineering at the Engineering and Environmental Office for the Volkswagen Group of America in Auburn Hills, MI. The 3.0-L V6 TDI meets EPA Tier 2 Bin 5 and California's ULEV II emissions standards. And the clean diesel engine—which uses a Bosch-supplied 2000-bar (29.0-ksi) piezo injection system and an exhaust gas recirculation system supplied by Pierburg and Cooper—exceeds the Euro 6 emissions standards outlined for 2014.

According to Schiele, "absolutely new technology" is employed on the engine's second and fifth cylinders. "Cylinder pressure sensors are used to detect a poor fuel quality and adjust the injection strategy to eliminate possible surging, noise, and associated driveability problems," said Schiele.

Vehicle performance is enhanced by a special variable-vane turbocharger supplied by Garrett. The exhaust gases coming from the engine spins the turbine wheel up to 200,000 rpm, according to Schiele. "The vanes control the speed of the turbocharger by directing the exhaust flow," said Schiele. "The speed of the turbocharger is directly related to the boost pressure supplied to the engine to a maximum of 1.6 bar."

The V6 TDI uses a special bypass-flap that is located between the intercoolers and the intake manifold. "Under certain conditions, this flap bypasses the intercoolers and delivers compressed air directly from the turbocharger to the engine. When this bypass-flap is activated, it helps the engine come up to operation temperature faster, which also has a positive effect on emissions," said Schiele.

A new exhaust system features a diesel oxidation catalytic converter to eliminate hydrocarbons and carbon monoxide, a diesel particulate filter to reduce soot, and a de-NOx converter. "AdBlue is injected in small amounts upstream of the de-NOx converter. The exhaust gases break the AdBlue down to create ammonia, which converts the NOx into nitrogen and water," said Schiele. The AdBlue tank capacity is 6 gal (23 L). "Refill of the AdBlue is done during recommended maintenance intervals," said Schiele.

In early 2009, the Q7 becomes the first Audi TDI with the ultra-low-emissions system in the U.S. The A3 is very likely to be offered with a 2.0-L four-cylinder TDI, and it is possible that other Audi models with clean-diesel technology will be offered in the U.S. At present, a 2.0-L four-cylinder TDI Jetta is sold in the U.S., and Volkswagen also will introduce a clean diesel in its Touareg early in 2009.

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