Since the enactment of lowered NOx standards by the EPA on January 1, 2010, all of the leading heavy-duty diesel engine manufacturers have been installing the Selective Catalytic Reduction (SCR) systems on the vast majority of their engines. With this modification, a routine addition of the Diesel Exhaust Fluid (DEF) is required to keep the engine running. 

What is DEF?

Diesel Exhaust Fluid (DEF) is a urea-based fluid specifically engineered for diesel engines as the reducing agent in Selective Catalytic Reduction (SCR) systems, which is a new vehicle technology platform for reducing NOx emissions through exhaust aftertreatment. DEF is a solution made up of purified water and 32.5 percent urea that is used as a carrying agent for the ammonia needed to reduce nitrogen oxide (NOx) emissions from diesel engines into nitrogen, water and carbon dioxide (CO2).

What is SCR?

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 emission to near-zero levels while also delivering a 3-5% fuel saving distinguishes SCR as one of the only emissions control technologies that is as good for business as it is for the environment.

SCR technology is designed to permit nitrogen oxide (NOx) reduction reactions to take place in an oxidizing atmosphere. 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 along can achieve NOx reductions in excess of 90%.