DEF, How does it works


Emissions regulations have been on the minds of diesel pickup owners, prospective owners, and professional over-the-road drivers for some time now. It began with the implementation of exhaust gas recirculation (EGR) systems, then progressed to the diesel particulate filter (DPF), and now the buzz is around selective catalytic reduction (SCR). Selective catalytic reduction systems use a consumable diesel exhaust fluid (DEF) in conjunction with a catalyst to reduce nitrous oxide (NOx) emissions. Because the fluid is consumed during the system’s normal operation, it requires the vehicles owner to not only monitor the fluids level but also refill it when it’s been used up.

What is Selective Catalytic Reduction (SCR)?

SCR is a technology that uses a urea based diesel exhaust fluid (DEF) and a catalytic converter to significantly reduce oxides of nitrogen (NOx) emissions. SCR is the leading technology being used to meet 2010 emission regulations.

How does an SCR system work?

The purpose of the SCR system is to reduce levels of NOx (oxides of nitrogen emitted from engines) that are harmful to our health and the environment. SCR is the aftertreatment technology that treats exhaust gas downstream of the engine. Small quantities of diesel exhaust fluid (DEF) are injected into the exhaust upstream of a catalyst, where it vaporizes and decomposes to form ammonia and carbon dioxide. The ammonia (NH3) is the desired product which in conjunction to the SCR catalyst, converts the NOx to harmless nitrogen (N2) and water (H2O).


What is Diesel Exhaust Fluid (DEF)?

DEF is the reactant necessary for the functionality of the SCR system. It is a carefully blended aqueous urea solution of 32.5% high purity urea and 67.5% deionized water. It is standardised as AUS 32 (aqueous urea solution) in ISO 22241. DEF is used as a consumable in selective catalytic reduction (SCR) in order to lower NOx concentration in the diesel exhaust emissions from diesel engines.

What is urea?

Urea is a compound of nitrogen that turns to ammonia when heated. It is used in a variety of
industries, including as a fertilizer in agriculture.



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