Urea (DEF) Diesel exhaust fluid
Diesel exhaust fluid (DEF), commonly referred to as AdBlue in Europe, Australia, and New Zealand, and standardised as ISO 22241 is an aqueous urea solution made with 32.5% high-purity urea (AUS 32) and 67.5% deionized water. DEF is used as a consumable in selective catalytic reduction (SCR) in order to lower NOx concentration in the diesel exhaust emissions from diesel engines.
DEF is used in Daimler AG's BlueTec system that has been built into several diesel trucks and cars. The German Association of the Automotive Industry (VDA) controls the "AdBlue" trademark and uses it to ensure quality standards are maintained in accordance with DIN 70070 and ISO 22241 specifications.