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Selective Catalytic Reduction (SCR) with NH3 or urea is one of the most effective methods for removal of NOx in exhaust from HD diesel engines with potential for achieving more than 90% NOx-reduction measured in the European transient or a US HD FTP test cycle. The present paper describes the following two systems; One OEM UREA-SCR SILENCER, comprising a silencer with built-in catalyst. The system was tested on a Scania DC1205 320 kW diesel engine, which was calibrated for the Euro II emission standard. The test results showed that it is possible to reduce more than 85% of the NOx emission with an insignificant NH3 slip in the ETC transient test cycle. The pressure-drop of the system was measured at 80% of that of the engine's original silencer and the silencing performance was improved for low frequencies below 125 Hz. One RETROFIT UREA-SCR SYSTEM for HD engines, comprising a silencer with built-in catalyst, an electronic urea injection control system, urea injection and a urea tank.

This paper discusses the choice of catalyst types to reduce the NOx emissions down to the Euro V level. A novel Urea injection system is also presented, which is based on a mass produced digital dosing pump that is combined with an electronic control unit specially developed for controlling the Urea-SCR process onboard vehicles. It is shown that it is possible to have a NOx conversion above 80% with ammonia slip below 10 ppm using 30 liters of 130 cpsi catalysts for a 12 diesel engine. By increasing the cell density to 300 cpsi it is possible to reduce the catalyst volume by 2/3 down to 20 liters for the same engine.