What Is SCR
Selective Catalytic Reduction

Selective Catalytic Reduction - (SCR) is one of the most cost-effective and fuel-efficient vehicle emissions control technologies available to reduce diesel engine emissions. For passenger cars and light duty trucks, the ability to meet strict emissions and fuel efficiency guidelines affordably without compromising driving power and performance is attractive. In commercial trucking, the ability to reduce emissions to near-zero levels while also delivering a 3-5% fuel savings distinguishes SCR as one of the only emissions control technologies that is as good for business as it is for the environment.

Did you know - According to an online study conducted in November 2008, 53% of truck buyers will likely consider the purchase of SCR to meet the 2010 EPA standards, compared to only 29% that will likely consider increased EGR.

How SCR Works

SCR technology is designed to permit nitrogen oxide (NOx) reduction reactions to take place in an oxidizing atmosphere. It is called "selective" because it reduces levels of NOx using ammonia as a reductant within a catalyst system. The reducing agent reacts with NOx to convert the pollutants into nitrogen, water and tiny amounts of carbon dioxide (CO2) - natural elements common to the air we breathe everyday. The reductant source is usually automotive-grade urea, otherwise known as Diesel Exhaust Fluid, which can be rapidly hydrolyzed to produce the oxidizing ammonia in the exhaust stream. SCR technology alone can achieve NOx reductions in excess of 90%.

Diagram 1: (A) Particulate matter trapped in aftertreatment device. NOx continues to flow downstream. (B) DEF injected into the exhaust stream. (C) DEF mixes with NOx. (D) NH3 and NOx react in the catalyst to form nitrogen and water. (E) Nitrogen and water vapor enter the environment.

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