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To reach the very strict Euro VI regulations of PM and NOx for heavy-duty trucks, it will be necessary to apply integrated catalytic solutions for removal of both PM and NOx. The most cost-effective solution would be to base the Euro VI system on Euro IV/V base engines, without EGR, and apply a high efficiency aftertreatment system, able to reduce the NOx from the common 7-8 g/kWh down to the Euro VI level at 0.4 g/kWh. The described system consists of a catalytic configuration, where the SCR catalyst is placed directly downstream of the diesel engine followed by an ammonia slip catalyst (ASC) and diesel injection over an oxidation catalyst (DOC) and a catalyzed diesel particulate filter (cDPF).

To reach the EPA ‘10 and Euro VI strict regulations of PM and NOx for heavy duty trucks it will be necessary to apply integrated catalytic solutions for removal of both PM and NOx. The described system consists of an alternative catalytic configuration where the SCR catalyst is placed downstream of the diesel engine followed by diesel injection over an oxidation catalyst (DOC) and a catalysed diesel particulate filter (cDPF). One of the advantages of this system configuration is that the SCR catalyst in this way is protected from high temperatures during filter regeneration and that the SCR catalyst has the fastest heat up required for good performance in cold test cycles. The SCR catalyst can therefore be of a standard V-based type that is already proven technology for Euro IV and Euro V compliance in Europe. Another advantage is that the DOC and cDPF act as clean-up catalysts for any possible ammonia slip from the SCR catalyst.

In order to meet the Euro V heavy-duty diesel emission standard legislation limits, a diesel engine can be optimized by internal means to give low particulate emissions and lower fuel consumption. These modifications of the engine lead inevitably to higher NOx emissions due to the NOx/PM trade off. An efficient Urea SCR after-treatment system is then able to reduce the higher NOx emission to below the Euro V 2.0g/kWh legislation limit. This paper presents tests made on a PM optimized 12 liter heavy-duty diesel engine together with a urea SCR after-treatment system. The optimized engine had engine out particulate emissions of about 0.04 g/kWh and NOx emissions of 9 g/kWh for the ESC and 8,5 g/kWh for the ETC. The fuel consumption of the optimized engine was 194 g/kWh for the ESC and 198 g/kWh for the ETC as compared to state of the art Euro III engines of typically 210 g/kWh for the ESC, giving significant fuel savings of 7.5 %.

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.

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.