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Twin Dosing – Volkswagen’s Exemplary Process Of Reducing Harmful Emissions

Jul 14, 2020 | Motopedia


In February, the Geneva Motor Show was cancelled due to Coronavirus or COVID-19. Following that, in March 2020 Volkswagen unveiled its hot hatch in a bold new avatar, the 2021 VW Golf GTD. With this, the manufacturer also announced that this car will be powered by a newly designed diesel engine that will not only be cleaner but also a great performer.

2021 volkswagen golf gtd

The 2021 Volkswagen Golf TDI was launched with a brand new diesel engine with Twin Dosing technology.

As mentioned by the Volkswagen in their press release, the new Golf GTD will be powered by a brand new diesel engine that not only gets bumped-up performance but is also economical and environment friendly. As mentioned in the press release:

“The Performance TDI’s efficiency has been significantly optimised and CO2 emissions have been cut even further, all while simultaneously improving responsiveness.”

To make this possible, Volkswagen revisited its basics and from the ground-up, it designed a brand new diesel engine. It also appointed a brand new technology which it calls “Twin Dosing SCR”. But what is it? Let’s find out.


What is Twin Dosing?

According to Volkswagen, Twin Dosing is a process which helps in reducing the nitrogen oxides in the exhaust gas from diesel engines. According to the German marquee, this process significantly drops the NOX values by around 80%. That’s an impressive feat by Volkswagen. But still, we don’t know how it works, so let’s dive deeper into it.

Twin Dosing, as the name suggests is a process in which the exhaust gases are treated not just once, but twice – before getting released in the air. As we know that the exhaust gas is a mixture of various components, including some harmful components like the NOx. To filter these and reduce the harmful effect, catalytic converters and particulate filters are used. Unlike the previous diesel engines with just one catalytic converter, this new engine uses two of those and this helps greatly in reducing the NOX values.

vw golf gtd twin dosing

Twin Dosing is a pretty neat technique used by Volkswagen to make its new diesel engines cleaner, economical & sporty.

In the case of Twin Dosing, Volkswagen redesigned its TDI engine and used 2 SCR or Selective Catalytic Reduction systems. VW renamed this new TDI engine to ‘EA288 evo’. This engine comprises of not just one catalytic converter but 3. One fitted directly to the engine.

The first SCR catalytic converter houses inside a component with a diesel particulate filter behind it. The second SCR catalytic converter sits at a distance from the engine, in the underbody of the vehicle.

Now we know about the placement of the SCR filters, let’s move ahead to the working of this process.


How does Twin Dosing work?

Twin Dosing is an innovative method of reducing nitrogen oxides. This process also incorporates a double injection of AdBlue into the exhaust. AdBlue is a term given to the reducing solution or agent that is selectively injected upstream of two SCR catalytic converters in an aqueous form to reduce the nitrogen oxides. We’ll talk more about this later in the article.

Mentioned below is the whole process in a step-wise manner:

2021 Golf GTD engine

A view of the combustion chamber inside the diesel engine of the new 2021 Volkswagen Golf TDI.

In the combustion chamber, the exhaust gases are formed and they contain harmful components. The gases first go into the oxidation catalytic converter where uncombusted fuel and carbon monoxide is removed.

The gases move from the combustion chamber into the Oxidation Catalytic Converter where unburnt fuel and Carbon monoxide are removed.

The gases move to the diesel particulate filter where the soot particles are filtered out. This step is significant as the diesel particulate filter act as the first SCR catalytic converter in conjunction with the AdBlue reducing agent. In this step, the first dose of AdBlue is injected in the exhaust, thereby reducing the NOX. NOX catalytic converters achieve their ideal working conditions at specific temperatures.

VW golf tdi twin dosing

Diesel Particulate Filter removes soot particles from the exhaust.

As the first filter is placed close to the engine, it heats up faster and thus works efficiently, especially during cold weathers or during slow city driving, and if necessary, the engine can accelerate the heating process. So this makes these filters not just helpful but intelligent too.

Twin dosing in vw golf 2021

This is the first stage where AdBlue is injected to reduce NOx or nitrogen oxide levels from the exhaust. This is the first SCR Catalytic Converter.

Coming to the second SCR filter that is situated in the car’s underbody. There also, the AdBlue is added to further reduce the nitrogen oxides in the gases. The temperature at which the gases enter the second stage is around 100°C. All these conditions ensure almost complete elimination of the nitrogen oxides. This makes the second filter as important as the first as this can work in any driving situation.

Vw 2021 golf tdi adblue

This is the second stage where AdBlue is injected to further reduce NOx or nitrogen oxide levels from the exhaust. This is the second SCR Catalytic Converter placed below the car’s floor.

Both the catalytic converters work simultaneously and ensure maximum removal of the harmful nitrogen oxides in the residual gases.


What is AdBlue and How It Works with Twin Dosing?

AdBlue is a special term given by the engineers at Volkswagen to an ammonia-based aqueous solution which is injected twice into the exhaust to significantly reduce the presence of nitrogen oxides in the exhaust gases. It is a reducing agent and though it sounds technical, its working process is very simple to understand.

2021 VW golf gtd twin dosing

Both the Catalytic Converters work together to bring the NOx levels significantly down by around 80%.

The SCR coating is a special coating done on the honeycomb structure of the filter which enables a single component to perform multiple tasks. When the AdBlue solution is injected into the exhaust, it evaporates and splits to combine with the steam to form ammonia. As the gaseous mix enters the SCR converter, the ammonia reacts with the nitrogen oxides NOX in the presence of the special coating. Due to this reaction, the harmful nitrogen oxides get converted into water and harmless nitrogen (N2) gas that is the main constituent of the air we breathe in.


How Twin Dosing Performs In The Real World?

Volkswagen had its equipment tested by two individual institutes who shared positive feedback about its performance. Not just in experimental conditions, the rig, when tested for real driving emissions or RDE, the outcomes confirmed that the Twin Dosing does reduce the NOX emissions by around 80% when compared to previous generation diesel engines.

2021 VW golf gtd

As per the experiments in various real-world scenarios, findings confirmed the reduction in NOx levels by around 80%.

VW first used Twin Dosing in the 2019 Passat 2.0 TDI and has got positive results. In 2020, VW introduced this technology in the 2020 Golf GTD. VW also plans to introduce this technology to all of its TDI models in the future.


Does Twin Dosing Have Any Impact On The Driving Experience?

Diesel engines are known for their smoothness, extended range and powerful torque. Volkswagen claims that Twin Dosing doesn’t affect the driving experience in any way. It maintains the smoothness of the drive while maintaining long-range and torque, thereby giving the best possible driving experience. Along with these, it also enhances the above-mentioned qualities and reduces fuel consumption and emissions.

2021 golf tdi

Volkswagen confirms that Twin Dosing doesn’t have any negative impacts on the driving experience but rather enhances it.

As Volkswagen mentioned in their press release

“The RDE measurements are considered to be particularly conclusive because they are taken while the vehicle is actually moving and not on a rolling road test bed with reproducible results as is usually the case.”

Markus Köhne, Head of Diesel Engine Development at Volkswagen, quotes:

“Our diesel engines are therefore not only extremely efficient, powerful and generate a high torque – they also contribute to a cleaner environment. We are extremely proud of this.”

So today, we learnt a new and an ingenious way that Volkswagen took to make its diesel engines cleaner and efficient while maintaining their power. With the new Twin Dosing technique, Volkswagen has boldly stated that diesel engines still have a long way to go.



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