Diesel Exhaust Fluid (DEF), also known as automotive-grade urea, chemically reduces nitrogen oxide emissions produced by diesel engines. It’s the key ingredient in the Selective Catalytic Reduction (SCR) process, which is one of the most effective means to reduce emissions to meet the new standards. During the SCR process, DEF is injected as a fine mist into the hot exhaust gases. The heat creates a reaction that turns the DEF into ammonia that when combined with a special catalytic converter breaks down nitrogen oxide into nitrogen gas and water vapor, two natural  components of the air we breathe. SCR-equipped trucks require a separate tank to hold DEF prior to mixing it with exhaust gases, and drivers must maintain DEF levels in their tanks.

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