SCR System Description

SCR System Description






The SCR (Selective Catalytic Reduction) system has been adopted on the exhaust gas after treatment device in order to comply with 2010 Exhaust Emission Regulations (US10). The SCR system eliminates NOx contained in the exhaust gas from the diesel engine by converting it into harmless Nitrogen by means of reductive reaction. The Diesel Exhaust Fluid (DEF) is used to induce the reductive reaction, and the reaction is facilitated through the SCR catalyst.

The Diesel Exhaust Fluid (DEF) control module calculates the target DEF injection amount based on the information from the engine control module (ECM), NOx sensors, etc., and injects the DEF that has been pressurized by the DEF supply module, from the DEF injector installed on the exhaust pipe. The DEF injected into the exhaust pipe is hydrolyzed by the heat from the exhaust gas, generating ammonia, and the generated ammonia induces reductive reaction with NOx, which decomposes NOx into water and nitrogen, as the result, emission of NOx is reduced.

NOx Reduction Mechanism

The DEF ((NH2)2CO+H2O) injected from the DEF injector is hydrolyzed by the heat from the exhaust gas, generating ammonia (NH3). The generated ammonia (NH3) induces reduction of nitrogen oxide (NOx) and decomposes NOx into nitrogen (N2) and water (H2O).






(1) The DEF ((NH2)2CO+H2O) is hydrolyzed by the heat from the exhaust gas, generating ammonia (NH3).
(2) The generated ammonia (NH3) induces reduction of nitrogen oxide (NOx) through the SCR catalyst and decomposes NOx into nitrogen (N2) and water (H2O).