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AdBlue and Clean Diesels

Another Way to Clean up Diesel Emissions

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2009 Mercedes-Benz BlueTEC GL

The Mercedes-Benz GL 320 BlueTEC diesel uses AdBlue injection

© Mercedes-Benz

What is AdBlue?

AdBlue is the German brand name for a clear, non-toxic—though slightly corrosive to some metals—aqueous urea solution used to treat exhaust on modern clean diesel engines. The generic name for a chemically equivalent solution used in the non-European market (predominantly North America) is Diesel Emissions Fluid (DEF).

What Does AdBlue Do?

Used in conjunction with a Selective Catalytic Reduction (SCR) converter, AdBlue has a profound effect on otherwise difficult to control oxides of nitrogen (NOx) diesel emissions. On average, NOx emissions are reduced on the order of approximately 80 percent. The AdBlue solution is comprised of 32.5 percent high purity urea diluted in distilled water and carried onboard the diesel vehicle in a special independent tank. Under the direction of the onboard computer and an NOx sensor, the fluid is pumped into the exhaust stream at the rate of 2 to 4 ounces to a gallon of ultra low sulfur diesel fuel (ULSD) consumed. And it is here, in the hot exhaust stack, where the urea solution is converted into ammonia (NH3) which reacts with NOx in the exhaust. The resulting chemical break down and re-bonding of the constituent elements of each reactant produces plain nitrogen and water vapor.

How and Where is AdBlue Replenished

Refilling the AdBlue tank is not a DIY task. Though it is possible to purchase the solution at the retail level, it is generally available only through a dealership or service shop. The systems are designed with a capacity of several gallons (seven to ten) which translates into several thousands of miles. Under normal vehicle operating conditions, the AdBlue tank needs to be refilled only during regularly scheduled maintenance.

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