Diesel Exhaust Fluid

EPA’s 2010 diesel engine emission standards will require engine manufacturers to further reduce the amount of nitrogen oxides (NOx) emitted.  To reach these NOx emissions levels, several engine manufacturers will employ selective catalytic reduction (SCR) as an aftertreatment technology that when combined with exhaust gas recirculation (EGR), will reduce NOx emissions to the level prescribed by EPA’s 2010 standards.  SCR is a proven technology that is currently being used in mobile applications in Europe & stationary applications here in the US.  The combined SCR/EGR NOx reduction system needed to meet EPA’s 2010 standard is new.

To reduce NOx, a small amount of urea-based solution called diesel exhaust fluid (DEF) is injected directly into the exhaust upstream of a catalyst.  The DEF vaporizes and decomposes to form ammonia (NH3), which in conjunction with the SCR catalyst, reacts with NOx to convert the pollutant into nitrogen (N2) and water (H2O).  This means that trucks will have to carry a sufficient quantity of DEF on-board.