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Diesel is saved? Volkswagen found a way to reduce NOx emissions by 80%

Posted September 3, 2019

People don’t really like diesel cars that much, even though at one point they were considered to be the future. Diesel fuel is more energy-dense than petrol and, therefore, diesel engines are more efficient. The problem is NOx emissions, which are associated with cancer and other health problems. But now Volkswagen found a solution, which will cut NOx emissions by 80 %.

Twin dosing is essentially a double SCR with two catalytic converters and two AdBlue injection points. Image credit: Volkswagen

Diesel cars use less fuel and emit less CO2. They also produce more low-end torque, which allows for smoother acceleration off the line and lends itself to making pretty interesting sports cars. However, diesel fuel combustion takes place with excess air. Since air is mostly nitrogen, nitrogen oxides (NOx) form and are released into the atmosphere. Scientists have identified NOx to be cancerogenic and that is why diesel cars are not welcome in many major cities in Europe.

Volkswagen invented a SCR (selective catalytic reduction) technology and has been using it for a year. Basically, an aqueous reducing agent (AdBlue) is injected upstream of SCR catalytic converter. It forms ammonia NH3, which then meets NOx in the converter. The result – N2 and H20 emissions, which are both harmless. However, this system does not work always. The best conversion ratios (around 90 %) are reached when the temperature of the gases is 220-350°C. This means that when the car is pulling uphill, accelerating aggressively or when it is cold, NOx emissions are greater. But now Volkswagen has a solution – next generation of SCR will feature a twin dosing system.

Volkswagen Passat 2.0 TDI Evo is likely to be the first to get twin dosing SCR, but other TDI engines will follow suit. Image credit: Volkswagen

Essentially, twin dosing SCR will have two catalytic converters and two AdBlue injection points in front of them. The second converter will be further downstream from the engine, which means that colder gases are going to reach it. This will open up the window of efficient conversion.

For example, 450°C gases may pass uncleaned through the first converter, but when they will reach the second one, they will be cooled down enough for the efficient conversion to occur. Volkswagen says that even at exhaust gas temperatures close to the engine of +500°C, the system is still able to achieve very high conversion rates. The result – NOx emissions can be reduced by around 80 %.

2.0 TDI Evo engine is the first one to get twin dosing SCR – Passant and the new Golf are going to have them. Soon after other TDI engines should get the twin dosing too. Of course, drivers will have to remember to fill up their AdBlue tanks, but these cars will meet Euro 6d emission standards.

Will this help diesel to make a comeback? It is difficult to say. People are looking to electric future more and more. But it will definitely help extending its lifespan for sure. 


Source: Volkswagen

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