Engine controls the production of particulate matter (PM), thus limiting it within the permissible value, while SCR is an exhaust after treatment device to reduce NOx. SCR spreads aqueous urea solution (AUS 32) into the exhaust stream. Ammonia from AUS32 combines with NOx in presence of catalyst to form harmless by-products like nitrogen and water vapor. Thus emitting clean gases. SCR technology is better positioned for heavy duty cycles (e.g. long haul heavy trucks & tractors, intercity bus etc.)
What is a SCR System?