SCR stands for selective catalytic reduction. It is the primary method used today in both Europe and the Unites States for the reduction of Nitrogen Oxide (NOx) which is the primary pollutant produced by diesel engines. Trucks running a SCR system contain a small tank used to store diesel exhaust fluid (DEF) which is mixture of water and urea. Through a complex process of sorcery, DEF is passed over a catalyst which transforms NOx into nitrogen gas and water vapor. As I mentioned before every truck manufacturer uses SCR except one. Why is that? The opponents of SCR highlight the complexity of the system citing the tanks for DEF, complex wiring, pipes and computers controls. Drivers must be trained to check and fill the DEF tanks which contain urea, this point is OFTEN highlighted. They really want you to make the connection between urea and urine. It maybe childish but that is marketing. DEF also begins to “slushify” around 12F. And finally attempting to to run a SCR engine without DEF will result in reduced performance, basically just enough engine power to limp along the shoulder.
What about ECR, AKA, exhaust gas recirculation. This is the method used by International in all their trucks and engine platforms. Instead of using fluid to transform or trap NOx, cooled diesel exhaust is recirculated through the engine which results in the complete destruction of the desired particulates. Opponents of ECR point to lower fuel economy and questionable pollution control results. Others claim the engines simply do not work and spend more time in the shop than on the road.
Just like anything in life there a pros and cons to each system. From the outside EGR offers the least amount of change for owners and drivers alike while SCR is a proven technology (as far as Europe is concerned) and appears to be the golden boy of the EPA and other regulatory bodies. Even though the EPA set standards for 2010 I don’t believe this issue has come to conclusion yet as truck buyers raced to stockpile premission trucks a few years back while truck builders continue to use engine credits and other loopholes to make “dirty” engines. Check out some of the videos below for all the details and some fancy truck related graphics. Knowledge is power!
Reasons for ECR
Reasons for SCR