Emission Reduction Fluid and Emission Reduction Fluid Handling: Chemistry

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Diesel engines run at over stoichiometric air-to-fuel ratio to ensure the combustion of soot and prevent unburned fuel from being emitted. The excess of oxygen necessarily leads to generation of nitrogen oxides (NOx), which are harmful pollutants, from the nitrogen in the air.
Selective catalytic reduction is used to reduce the amount of NOx released into the air using exhaust emission reduction fluid. Exhaust emission reduction fluid (from the exhaust emission reduction fluid tank located in large trucks) is injected in front of the SCR catalyst where it vaporizes and decomposes to form ammonia and carbon dioxide. With the SCR catalyst, the NOx are catalytically reduced by the ammonia (NH3) into water (H2O) and nitrogen (N2), which are both harmless and are released through the exhaust.