The U.S. Environmental Protection Agency (EPA) 2010 diesel emissions standards, which went into effect this month, are the world’s most stringent. To meet these standards, commercial truck and engine manufacturers have settled on two types of emissions control technologies: selective catalytic reduction (SCR) and exhaust gas recirculation (EGR).
SCR treats the engine exhaust downstream. EGR, also referred to as in-cylinder EGR and enhanced or advanced EGR, reduces emissions in the engine cylinder. Both SCR and EGR emissions systems control nitrogen oxide (NOx).