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Audi has been teasing us for a couple of years now with the possibility of a diesel version of its Q7 sport-utility vehicle , but so far the model has been missing its roll call. Alas, it finally will come to the U.S. by early calendar-year 2009, as a 2009 model, with an emissions system that’s 50-state legal.
In order to get the engine to meet the strictest U.S. standards, the Q7 TDI now includes a number of technologies that weren’t all used together in diesels until very recently. They include cylinder pressure sensors, NOx sensors, a second catalyst and, most importantly, a urea-injection system, which sprays the liquid directly into hot exhaust gases just ahead of the second catalyst, reducing NOx emissions and producing nitrogen and water instead from the tailpipe, without the use of precious metals or a cumbersome nature and maintenance needs of a NOx trap.
The urea solution, called AdBlue, will be stored in a 6.2-gallon tank, and lasts at least 10,000 miles — more than enough to get you to the next oil change — though, according to Audi engineers, that’s a worst-case-scenario. And the AdBlue is injected into the exhaust at a rate that isn’t directly proportional to mileage or fuel use, according to engineers, but depending on driving style, trip length, and other conditions such as outside air temperature.
We recently had the chance to drive the clean-running Q7 3.0 TDI in Ontario and were, as with a number of other diesel vehicles we’ve driven over the past several years, very impressed with its drivability, tremendous torque, and refinement.
The third-generation direct-injection system is the chief reason for the engine’s smooth idle, refinement, and good throttle response, along with its complete lack of sooty exhaust no matter how hard you drive it. Injection pressure is now maintained at about 29,000 psi, and high-precision piezo injectors help smooth out the combustion process. At low engine speeds, a pilot injection helps further smooth out the combustion process in addition to the five injections are made every engine cycle. Its glow plugs enable a cold start in the coldest outside temperatures after only two seconds.