The EPA 2010 rule pertaining to Air Quality Regulations for nitrogen oxides (NOx) and particulate matter (PM) emissions from diesel engines has forced manufacturers to radically redesign their engine and emission control systems. Almost unanimously, manufacturers have chosen Selective Catalytic Reduction (SCR) technology, a post-combustion emission reduction technology that relies on a product called Diesel Exhaust Fluid. DEF is a non-toxic, colorless liquid that acts as a reducing agent in the SCR system.
DEF is a high purity solution of urea in water. It is used in Selective Catalytic Reduction (SCR) equipped diesel vehicles to chemically reduce Nox emissions. DEF is contained in a separate tank and sprayed into the exhaust gases.
For medium and heavy duty vehicles, Diesel Exhaust Fluid consumption will be approximately 3% of your diesel fuel consumption (for every 200 gallons of diesel consumed you would need 1 gallons of DEF).
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.
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%.