Diesel Exhaust Fluid (DEF)
After legislation was passed to decrease hazardous diesel engine emissions throughout the U.S. and Europe, it was decided among most major manufacturers to incorporate the diesel system technology, known as Selective Catalytic Reductions (SCR), to be used in conjunction with a liquid-reductant agent, known as Diesel Exhaust Fluid (DEF-North America) or AdBlue (Europe), to further meet the new standards.
The SCR system works concurrently with the liquid-reductant agent (DEF or AdBlue). The reductant agent is released into the exhaust stream, the heat from the exhaust gas vaporizes the reductant agent (DEF or AdBlue), turning it into ammonia and carbon dioxide. The nitrogen and nitrogen oxide in the exhaust gas reacts with the ammonia once they come into contact with the catalyst, forming harmless nitrogen and water vapor. The vapor is then expelled back into the atmosphere through the tailpipe without causing substantial losses in efficiency and torque.