Volkswagen has introduced its cleanest ever TDI engine. Initial test drives conducted by VW has already showed promising results when the TDI engine was able to reduce nitrogen oxide. For Volkswagen's Jetta a new 2.0 liter commo9n rail diesel engine with nitrogen oxide reservoir catalytic converter was employed which conforms to the Californian emission standard 'Tier 2/Bin 5'-considered to be the most strict in the world. The first production of the TDI with nitrogen post treatment system will be made in 2008 in the US.

The main objective of the TDI engine is to reduce nitrogen oxide emission. Volkswagen's team of engineers in Wolfsburg is working on the development of the engine and the use of new emission post-treatment technology. They have already achieved 90% less nitrogen oxide emissions.

The said drastic reduction was needed in order to comply with the Tier 2/Bin 5 standard which applies to California and four other states in the north-east of America namely: Massachusetts, New York, Vermont and Maine. ---This norm limits Nox emissions to 70mg per mile. And in order to comply with this standard VW has decided to develop a completely new emission treatment technology.

Volkswagen was able to develop two new systems connected to the oxidation catalytic converter and the particle filter in the exhaust system. The new Nox reservoir catalytic converter technology is currently tested for car models below the Passat class. Nitrogen oxide is absorbed like sponge which leads to a high level of efficiency. And in terms of the particle filter, the system is regularly cleaned without the driver noticing it. How? The engine management system changes operation modes for a few seconds.

For Volkswagen's larger and heavier models, they will feature the Selective Catalytic Reduction (SCR) catalytic converter. The central component of the SCR is an aqueous solution such as AdBlue which is transported in an additional tank made from stainless steel or plastic. The aqueous solution is also made up of 32.5% Urea which is continuously injected into the exhaust system in front of the SCR catalytic converter using a metering valve. The quantity of the aqueous solution is made according to the gas emission stream.

The urea solution that is mixed with the aqueous 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 in into water and nitrogen.

The ammonia produce is not like the ordinary ammonia in the sense that it is non-toxic, odorless and biodegradable. Volkswagen also intends to install the additional tank so that the car may be driven without the need for maintenance between services. According to US regulations the complete system should be functional for at least 150,000 miles.