Selective Catalytic Reduction Technology – What is it?

After stringent legislation was passed to decrease hazardous diesel engine emissions throughout the U.S. and the European Union (EU) it was decided upon by most major manufacturers to incorporate the diesel system technology known as Selective Catalytic Reduction (SCR) to be used in conjunction with a liquid-reductant agent Diesel Exhaust Fluid (DEF - North American) or AdBlue (Europe) to further meet the new standards.    

The system which has been used for decades for cargo vessels, ferries and tugboats has finally made its way into diesel engines for over the road vehicles.  The EU directives were put into place starting in the early 1990’s but beginning in 2004 the European automobile industry started incorporating SCR technology in their Heavy Duty trucks, while the U.S. automotive industry began the transition a little later in 2010. 

How it Works

The SCR technology 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 turning it into ammonia and carbon dioxide (CO).  The nitrogen (NO) and nitrogen oxide (NO₂) in the exhaust gas reacts with the ammonia once they come into contact with the catalyst and in turn forms harmless nitrogen and water vapor that is expelled back into the atmosphere through the tailpipe without causing substantial losses in efficiency and torque.

SCR Technology

Into the Future

Currently all manufacturers have decided upon the SCR technology for their engines.  Demand is only expected to increase with other industries transitioning in the near future over to the SCR technology to meet the new standards set by governing bodies around the world.  

For more information on all things DEF, please see the following pages:




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