Volkswagen's Turbocharged Direct Injection (TDI) is said to be the leader in diesel revolution. TDI engine makes use of the Pumpe Düse system which makes it incredibly efficient. Pumpe Düse which means 'pump injector' have solved the problem of lost pressure through fuel pipes. The injector and pump are integrated in a single Pumpe Düse unit. Each of the cylinders has its own Pumpe Düse unit placed on the cylinder head and operated by the camshaft, injecting fuel directly into the combustion chamber at pressures ranging up to 30,000psi.

The high pressures produce is perfect for efficiently blending of the fuel/air mix, controlling fuel quantities and injection timings. Such clever technology enables TDI to offer the benefits it's famous for such as: good fuel economy, reduced exhaust emissions, and increased performance with more torque than the traditional injection systems.

Volkswagen didn't stop with the TDI technology; it has continuously developed and improved it until it has finally come up with the cleanest ever TDI engine. Initial test drives of the high potential Volkswagen technologies demonstrate a remarkable reduction in the emission of nitrogen oxide.

VW's Jetta with a new 2.0 Liter common rail diesel engine with a nitrogen oxide reservoir catalytic converter which complies to the Californian emission standard 'Tier 2/Bin 5' was used during the test. The Tier2/Bin 5 are considered to have the strictest requirements worldwide. The first production run of the 'Clean TDI' with nitrogen oxide post treatment will be made by 2008 in the US.

The main objective of the entire 'Clean TDI' concept is to reduce nitrogen oxide. Volkswagen's engineers in Wolfsburg reached this goal through the internal development of the engine and the use of new emission post-treatment technology giving them a result of up to 90% less nitrogen oxide emissions (NOx).

This result was necessary to comply with the Tier 2/Bin 5 norm which applies to California and four other states in the north-east of America namely Massachusetts, New York, Vermont and Maine. The average Nox emissions allowed is 70 mg per mile and in order to comply with the said standard Volkswagen has developed an entirely new emission treatment technology.

Volkswagen has developed two new systems connected to the oxidation catalytic converter and the particle filter in the exhaust system. At present new NOx reservoir catalytic converter technology is being tested for models below the Passat class. Nitrogen oxide is effectively absorbed like sponge which leads to a high level of efficiency. In terms of the particle filter, the system has a self-cleaning system. How? The engine management system changes operation modes for a few seconds.

For larger and heavier vehicles a Selective Catalytic Reduction (SCR) catalytic converter is employed. The central element of the SCR is an aqueous solution such as the AdBlue which is transported in an additional tank made from stainless steel or plastic. The solution contains 32.5% urea which is continuously injected into the exhaust system in front of the SCR catalytic converter using a metering valve.

AdBlue solution is a non-toxic, odorless and biodegradable. Volkswagen intends to install the additional tank so that the car can be driven without needing maintenance between services. VW is the diesel pioneer in the US and approximately more than 800,000 diesel cars from Volkswagen have already been sold.