What Is DEF?
Diesel Exhaust Fluid (DEF) is a water-urea solution (32.5% high-purity urea and 67.5% deionized water). It is non-toxic, nonflammable, non-hazardous and non-explosive.
The purpose of DEF is to reduce nitrogen oxide (NOx) concentration in the exhaust emissions produced by diesel engines. The process by which NOx emissions are reduced is called Selective Catalytic Reduction (SCR).
DEF is generally carried in a separate storage tank in diesel-powered vehicles equipped with SCR technology. DEF is injected into the hot exhaust stream of an engine and absorbed onto a catalyst. In this way it helps break down the NOx gases in the exhaust into nitrogen gas and water vapor, both harmless to the environment.