SCR is very simple. There are four major components to the SCR system: a Diesel Exhaust Fluid (DEF) tank, a DEF doser, the SCR catalyst, and an ammonia (NH3) catalyst. These components are all integrated into the exhaust system. Small amounts of DEF are injected into the catalyst where it is mixed and reacts with the NOx found in the exhaust to produce nitrogen gas and water vapor, both of which are harmlessly released into the atmosphere through the vehicle’s tailpipe.

 Benefits of SCR

Simply stated, SCR improves engine fuel economy and increases engine reliability. Compared to 2007 emissions technology, engines using SCR aftertreatment do notrequire significant increases in EGR flow rates to meet EPA 2010 NOx limits.Because the pollutants are reduced to near-zero levels within the exhaust stream,an engine with SCR aftertreatment will operate cooler, cleaner and more efficientthan engines with higher EGR levels. PACCAR engines with SCR technology willprovide up to 5% fuel economy improvement compared to today’s engines, and even greater when compared to a 2010 non-SCR engine. Also, a cooler engine provides greater reliability.