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VW's Clean Diesel (No, That's Not an Oxymoron)

The 2009 Jetta TDI is clean enough to be sold in all 50 states as it meets the demanding Tier 2, Bin 5 emissions requirements.

According to Allen Schaeffer, executive director, Diesel Technology Forum (www.dieselforum.org) an educational trade organization with membership including OEMs, engine manufacturers, component suppliers, emission control device manufacturers, and petroleum refiners-the 2009 Jetta TDI is a significant vehicle for a fairly simple reason.

According to Allen Schaeffer, executive director, Diesel Technology Forum (www.dieselforum.org) an educational trade organization with membership including OEMs, engine manufacturers, component suppliers, emission control device manufacturers, and petroleum refiners-the 2009 Jetta TDI is a significant vehicle for a fairly simple reason. For one thing, with the exception of Volkswagens, heretofore, diesel-powered cars were generally available from luxury marques, like Mercedes. They came with luxury price tags. And given the seemingly ever-increasing environmental regulations, the availability of diesel power in all 50 states has become a problem. But not with the new Jetta.

In the Volkswagen lineup, the Jetta, now on its fifth generation, is the volume leader in the North American market. In fact, because of its comparative popularity in the North American market, it is manufactured exclusively in Puebla, Mexico. ("German engineering" doesn't necessarily mean "German manufacturing." But the TDI diesel for the Jetta is produced in Chemnitz, Germany.) Through August, 2008 Jetta sales in the U.S. were 66,850 units. Coming in second was the Passat, at 23,976. Clearly, a lot of people who like VWs like the Jetta.

So by putting a "clean" 2.0-liter, 140-hp four-cylinder diesel engine under the hood of both the Jetta sedan and the SportWagen models, VW is putting a diesel powered vehicle within buying range of the mass market: The starting price for the sedan is $21,990 and the wagon $23,590. Which is about $2,000 more than the gasoline-powered vehicles.

But wait, says Norbert Krause of the VW of America's Environmental Engineering Office. There's more. He points out that there is additional content in the TDI models as compared with their gas-powered counterparts. In addition to which, there is a $1,300 Federal Advanced Lean Burn Technology consumer tax credit available for the car. Which brings the delta to about $100 between gasoline-power and diesel power. And given that the EPA mileage numbers for the Jetta TDI are 29 city, 40 highway with a six-speed double-clutch gearbox (DSG) and 30/41 for the six-speed manual, presumably there aren't a whole lot of visits to the service station before that $100 is more than made up for. (By comparison, the standard engine for the Jetta is a 2.5-liter, five-cylinder model that is rated at 21 mpg city/29 mpg highway.)

One of the drivers of diesel fuel economy is high combustion temperatures. That, however, contributes to the production of nitrogen oxides (NOx). So this is addressed in the Jetta turbodiesel by a number of ways, including the configuration of the common rail fuel system, high-pressure piezo injectors, and combustion chamber design. In addition to which, there is an exhaust system that handles the problem of NOx. There is a diesel particulate filter (DPF) that is connected to a NOx storage catalyst. When the differential pressure sensor determines the DPF is sufficiently loaded, it initiates a regeneration process that oxidizes the hydrocarbons and carbon monoxide so that they become carbon dioxide and water. The DPF also collects and filters the particulates in the exhaust. The NOx storage catalyst is described by Krause as "the magic part." It stores the NOx gases and then catalyzes them such that the output consists of nitrogen and water. There is no urea system-known in the diesel powertrain community as an SCR, or selective catalytic reduction, catalytic converter-involved. Krause explains that the AdBlue fluid isn't required because the engine is sufficiently small; for larger engines, the urea system is required. Even though the system uses ultra-low sulfur diesel fuel-which can have no more than 15 ppm of sulfur-sulfur is rather aromatic-think: rotten eggs. So even though there is far less sulfur in this fuel than there had been prior to October 2006-97% less-there is the potential that some whiff could be expelled. So there is an H2S slip catalyst that traps any odor before the end of the tailpipe.

A bottom line to this is that the 2009 Jetta TDI meets Tier 2, Bin 5 emissions requirements-the most demanding emissions standard in the world. Which makes the vehicle 50-state compliant-a first for diesel passenger cars.

While this is the first diesel of this type in the VW lineup-even though the 2.0-liter diesel engine is produced and used in VW vehicles built in Germany, the extensive exhaust system is not employed-the company has long sold diesel vehicles in the U.S.: 32 years. During this period, it has sold some 850,000 diesel-powered cars in the U.S. And it intends to sell a lot more.