|“Clean TDI” Tier 2 Bin 5 VW.|
Volkswagen is testing a Tier 2 Bin 5 compliant “Clean TDI” diesel powertrain—a new 2.0-liter diesel and a lean NOx trap—in a Jetta. Volkswagen says its “Clean TDI” vehicles will go into production in the US in 2008.
Volkswagen, which is a member of the BLUETEC initiative announced in November 2006, has also announced a concept “Clean TDI” Tiguan SUV. (Earlier post.)
|VW plans to use two types of emissions control systems. Click to enlarge.|
Volkswagen has developed two new systems connected to the oxidation catalytic converter and the particle filter in the exhaust system to meet the stringent NOx reduction requirements of the Tier 2 Bin 5 / CA LEV II standard (the threshold for sales in all 50 states of the US).
For car models of the Passat class and smaller, Volkswagen is testing its new lean NOx trap catalytic converter (discontinuous). At λ of greater than 1, NOx is captured and stored; at λ less than 1, NOx is released and reduced. Ultra low-sulfur fuel is a necessity, and fuel consumption will increase as a result of catalytic converter regeneration.
Larger and heavier models feature urea Selective Catalytic Reduction (SCR) catalytic converter (continuous) with the use of an aqueous solution such as AdBlue, transported in an additional tank made from stainless steel or plastic.
Urea comprises 32.5% of this solution, which is continuously injected into the exhaust system in front of the SCR catalytic converter using a metering valve. The dosage is made according to the gas emission stream.
The urea solution is finely atomized by a grille and is converted in hot exhaust gas into ammonia before it reaches the catalytic converter. The ammonia then reacts with the nitrogen oxide in the catalytic converter and separates it into nitrogen and water.
Volkswagen intends to install the additional tank so that the car can be driven without maintenance between services. For the US, the complete system must be fully functional for at least 150,000 miles.
BLUETEC is a joint project between Volkswagen, Audi and DaimlerChrysler, and is intended to establish the diesel engine further in the American car market. The manufacturers are promoting the diesel engine as a low-consumption alternative for future car use. Each of the manufacturers involved in the BLUETEC joint project is working on individual technical solutions for stringent exhaust gas emission standards and plans to market these independently.
Volkswagen has sold more than 800,000 diesel cars in the US to date.
LNT or Urea SCR Technology: Which is the Right Technology for Tier 2 Bin 5 Passenger Vehicles? (Volkswagen, DEER 2006)