Home » What is DEF

What is DEF

What is Diesel Exhaust Fluid

Diesel Exhaust Fluid (DEF) Definition:  A specific composition of urea for application in transportation to reduce the amount of nitrogen oxides (NOx) emitted into the air by diesel engines.  DEF is a high purity chemical, comprised of 32.5% urea and 67.5% de-ionized water.


Diesel Exhaust Fluid is produced to an international standard (ISO 22241).  In order to meet the 2010 EPA Diesel Emission Standards to reduce the amount of NOx emitted by diesel engines, several engine manufactures employed Selective Catalytic Reduction (SCR) as an after-treatment technology combined with Exhaust Gas Recirculation (EGR).


As explained by the American Trucking Association (ATA), “To reduce NOx, a small amount of DEF is injected directly into the exhaust upstream of a catalyst.  The DEF vaporizes and decomposes to form ammonia (NH3), which in conjunction with the SCR catalyst, reacts with NOx to convert the pollutant into nitrogen (N2) and water (H2O).” 



The Truth About SCR Medium

Medium Duty Truck Owners

The Truth About SCR Heavy

Heavy Duty Truck Owners


For questions about Diesel Exhaust Fluid, please contact your DEF area sales representative.


Print page