DPF + SCR

To achieve this high level of efficiency, all aspects of the system need to be optimized. An SCR system will generally comprise an ammonia delivery system, and the catalyst system itself comprises the DOC (and typically DPF), SCR catalyst, and the ammonia slip catalyst. 

DPF regeneration interval 700km for DPF-SCR SOOkm for SCR-DPF Fuel consumption increase during DPF regen S3% for DPF-SCR, 62% for SCR-DPF... 

Fig. 2.20 Shunting locomotive from Deutsche Bahn AG with a combined DPF + SCR installation (Picture MTU)...

Fig. 2.23 Measured temperature distribution in front of the DPF + SCR Reactor (Data MTU)...

Mussmann L, Muller W, Soeger N, Spurk P (2007) Combined DPF/SCR Concepts for Future Heavy Duty Emission Limits. Paper presented at thelst MinNox Conference, Berlin, Germany, 1-7 Feb 2007... 

Scarnegie B, Miller W, Ballmert B, Duelling W, Fischer S (2003) Recent DPF/SCR Results Targeting US2007 and Euro 4/5 HD Emissions. SAE Technical Paper 2003-01-0774... 

Engine-out---Tailpipe DPF-SCR —Tailpipe SCft-DEE — Tailpipe SCRF... 

Koltsakis G, Koutoufaris I, Haralampous O, Tourlonias P, Kramer L (2007) Model-based design of combined DPF-SCR systems for passenger cars. Paper presented at the FAD conference 2007... 

The main reactions, which have to be considered on SCR catalysts, are the standard-SCR, fast-SCR, and the N02-SCR reactions, beside the ammonia oxidation and the formation of N20. The fast-SCR reaction is promoted by N02 in the feed that can be generated from NO in a pre-oxidation catalyst. However, the right dimensioning of the oxidation catalyst is critical in order to prevent the production of an excess of hazardous N02. This problem is further aggravated if a continuous regenerating DPF is installed in front of the SCR system, as part of the N02 produced by the oxidation catalyst is always consumed in the filter for soot oxidation. 

The extended SCR model has been integrated with other catalyst and diesel particulate filter (DPF) models in the Daimler exhaust gas after-treatment systems simulation environment ExACT. The model was also extended to other SCR catalytic materials [79]. 

Diesel particulate filters (DPF), which remove particulate from the exhaust stream. They can also be coated with catalyst, e.g. DOC, LNT or SCR, to enable removal of gaseous pollutants in the same system component. 

Thus, the main function of the DOC is to oxidize CO and unburned HCs. The secondary function, utilized in combined exhaust aftertreatment systems, is the oxidation of NO to N02, which then enables optimum operation of the NOx aftertreatment catalysts placed down the exhaust line (NSRC and/or SCR, cf. Sections VI, VII and VIII, and also DPF). 

The different catalyst models within the simulation environment ExACT are used for the simulation of combined aftertreatment systems, when exhaust conditions for a catalyst are influenced by its upstream component and changes in one catalyst affect all components further down the line. An application example is given in the following section and in Chatterjee et al. (2006). It investigates a combined system of DOC and SCR catalyst. Further examples for such combined systems to be investigated are DOC and NSRC or combinations of different catalyst technologies with DPF. 

Finally, an application example for a combined aftertreatment system simulation has been given and discussed, investigating a combination of a DOC and a SCR catalyst. It shows how NOx conversions in the urea-SCR converter over the ESC and ETC driving cycles can be greatly improved by N02 formation in the DOC placed upstream. The system model is used to evaluate DOC size under steady state, but also under transient cycle operation. Further examples for such combined systems which can be investigated are DOC and NSRC or combinations of different catalyst technologies with DPF. 

The two major steps for diesel cars were the introduction of oxidation catalysts at the Euro 2 level and the effective mandatory introduction of DPFs at the Euro 5 level. For NOx, EGR has been the main tool to control emissions up to Euro 5. SCR systems for light-duty vehicles are starting to appear for passenger cars at the Euro 6 level. 

The technology for controlling emissions from heavy-duty vehicles has, until recently, focussed on in-cylinder measures such as direct injection (DI) and high-pressure injection (HPI, >150 MPa). However, at current and future emission levels SCR has become the NOx emission-control technology of choice, whilst DPFs will effectively become mandatory at the Euro VI level (Table 4). 

DPF= Diesel Particulate Filter EG R = Exhaust Gas Recirculation SCR = Selective Catalytic Reduction LNT = Lean NOx Trap... 

In addition to the SCR catalyst system (DOC, SCR, ASC, mixer) and the DPF, the other main components of the system are the urea delivery system, comprising the storage tank (DEF tank) and sensors, the heated delivery line, pump, and... 

Oxidize NO to NO2 (Reaction (1.4), above), which is used to continuously oxidize soot on a DPF, and for enhancing the fast SCR deNOx reactions (Reaction 1.2), particularly at low temperatures. 

Vanadia SCR catalysts are used in Europe, the emerging markets, and in some agricultural applications in the US, but not in Japan due to durability issues related to thermal exposure when DPFs are regenerated. Advances are now reported [36] on vanadate SCR catalysts that have no volatility up to 750 °C or higher, versus 550-600 °C for some commercial catalysts, giving them similar HT durability to... 

---