What kind of chemistry do you have with your car? Love it? Loathe it? Let us know and you could win a £300 John Lewis voucher | No thanks

VW 'Twin Dosing' of AdBlue Reduces NOx Emissions by 80%

Published 02 September 2019

SCR 'Twin-Dosing' introduced in the VW Passat 2.0TDI Evo 110kW has reduced NOx emissions by 80%.

Adblue is injected selectively upstream of two SCR catalytic converters which are arranged in series. The system is used in the new Passat 2.0 TDI Evo with 110 kW (150 PS), which already meets the technical requirements of the future Euro 6d emission standard as a result. Current RDE1 (real driving emissions) measurements confirm Volkswagen's type approval.

Volkswagen will now gradually introduce the new technology to all models with 2.0 TDI Evo engines. The new 2020 Golf VIII will features twin-dosing in all TDI variants.

Twin dosing requires a second SCR catalytic converter located under the car. Since the distance to the engine is greater, the exhaust temperature upstream of the second catalytic converter can be as much as 100°C lower. This expands the window for aftertreatment of exhaust gases, so even at exhaust gas temperatures close to the engine of +500°C, the system is still able to achieve very high conversion rates. In addition, a blocking catalytic converter downstream of the SCR system prevents excess ammonia slip.

VW provides a very clear explanation of the problem with diesel engines and the solution. 

This twin dosing process compensates for a fundamental disadvantage of diesel engines. Modern diesel engines emit less CO2 than petrol engines because diesel fuel has a higher energy density and the combustion process is more efficient. Diesel engines are also subject to special emissions requirements, however, since fuel combustion takes place with excess air. The main constituent of air is nitrogen and this reacts with oxygen during combustion, thereby forming nitrogen oxides.

Ammonia is needed to reduce these nitrogen oxides. It is injected as an aqueous reducing agent (AdBlue) via a dosing module into the exhaust gas upstream of an SCR catalytic converter. Here, the solution evaporates; the reducing agent is split, combining with steam to form ammonia. In the SCR catalytic converter, the ammonia (NH3) then reacts on a special coating with the nitrogen oxides (NOx) to form water and harmless nitrogen (N2) – the main constituent of the air we breathe.

In existing exhaust gas treatment systems, a close-coupled SCR catalyst is located between the turbocharger, the diesel oxidation catalytic converter – which converts uncombusted hydrocarbons – and the flexible connecting piece to the silencer pipe. The SCR coating is applied to the honeycomb structure of the diesel particulate filter, thereby enabling a single component to perform several functions. The close-coupled arrangement means that the exhaust gas temperatures required for high conversion rates can be achieved quickly after a cold start – the ideal range for conversion rates of more than 90 percent is between +220°C and +350°C. These conditions are met in many operating situations.

Conversion rates do not drop above +350°C – thanks to twin dosing-system. Temperatures at this level occur for example when driving at high speeds on the motorway, at high engine speeds over prolonged periods of time and when driving uphill, especially if the vehicle is fully loaded or towing a trailer.

1) Passat Saloon 2.0 TDI Evo 110 kW / 150 PS (NEFZ) fuel consumption in l/100 km: urban 4,5 / extra-urban 3,5 / combined 3,9; CO2-emissions in g/km: 101; efficiency class: A+  Passat Estate 2.0 TDI Evo 110 kW / 150 PS (NEFZ) fuel consumption in l/100 km: urban 4,5 / extra-urban 3,6 / combined 4,0; CO2-emissions combined in  g/km: 104; efficiency class: A+ 

Comments

beatbox    on 2 September 2019

How about a TWIN DOSING of customer services?

And a real retrograde fix for the VW 1.5 tsi kangarooing engine.

And a six year warranty which they offer to American customers.

"Volks, then wagen. People, then car.

That’s our philosophy, and that means being there for our customers long after they drive off the lot. That’s why we offer America’s Best Car and SUV Bumper-to-Bumper Transferable Warranty on almost all of our 2019 models.

The Volkswagen 6 years/72,000 (whichever occurs first) Miles New Vehicle Limited Warranty.

It’s perfect for America’s best customers."

But, not perfect to Britain's best customers.

Edited by beatbox on 02/09/2019 at 11:01

Add a comment

 

Ask Honest John

Value my car