Selective Catalytic Reduction (SCR) is a post-combustion technology treatment for diesel vehicles. This process requires a diesel exhaust fluid, namely AdBlue, to be injected into the exhaust pipe after the engine (post combustion) to help convert the poisonous NOx (Nitrogen Oxide) found in the vehicles emissions, into harmless water and nitrogen. AdBlue contains deionised water and 32.5% automotive grade urea, a compound of nitrogen.
AdBlue is a colourless, non-toxic, non-polluting and non-flammable solution. When the fluid gets hot (in the exhaust), the water evaporates and the urea converts to ammonia. The ammonia reacts with a special catalyst in the SCR muffler and converts the NOx to harmless nitrogen and water. Special sensors in the tailpipe monitor the amount of NOx being released and adjust the injection of AdBlue to control the NOx output to required levels.
AdBlue, combined with SCR technology, is an efficient solution to reduce emissions of NOx from diesel engines. Compared to competing solutions like EGR technology, SCR catalyst technology allows much greater NOx conversion efficiency without creating a need for greater cooling capacity, coupled with power reductions, oil degradation issues, reductions in engine durability and fuel efficiency.