The SCR system (Selective Catalytic Reduction) is an emissions control technology incorporated into cars in order to minimize nitrogen oxide (NOx) emissionss Main functions of the SCR system are to break down NOx emissions into harmless nitrogen and water vapour This is achieved through a chemical reaction catalyzed by a catalyst and the injection of a liquid reductant agent, typically diesel exhaust fluid (DEF). Characteristics of the SCR system include precise DEF injection systems and advanced sensing technology and an SCR catalyst. These components work together to control exhaust gas conditions accurately, in order to attain peak emissions reduction. SCR technology is widely used in various types of diesel vehicles, from passenger cars to heavy-duty trucks The power of mid-class engines is poised for deployment in the marine sector and beyond as a result marine emissions can be reduced to almost nil by using exaust aftertreatment. All diesel engines on trucks made since 2009 use SCR technology.