Exhaust gas aftertreatment systems

Fig. 5. Example of a combined exhaust gas aftertreatment system model.

As discussed in Section 1.2, legislation has moved towards a further reduction in the tailpipe emissions of CO, HC and NO. To meet this requirements, changes in the design of the engine and of the catalytic exhaust gas aftertreatment system are planned, eventually along with a reformulation of the fuel. 

P.L. Herzog, P. Zelenka "Automotive Application of Exhaust Gas Aftertreatment Systems toward Clean Diesel Engines." CIMAC Conference (FISITA Session), May 15-18, 1995, Interlaken, Switzerland. 

The emission of nitrogen oxides (NOx) from automotive and stationary sources causes serious environmental concern. Automotive exhaust gas aftertreatment systems are commonly based on precious metal catalysts (three way or diesel oxidation catalysts). One undesired effect during NOx reduction with these catalysts is the formation of N2O, which is now considered to be an environmental pollutant also [1,2], In this report the generation of N2 and N2O during NOx decomposition or reduction on Pt/alumina is investigated. 

Fig. 2.4 Influences and roots of off-highway exhaust gas aftertreatment systems (Pictures MTU)...

Figures 2.17 and 2.18 show a typical setup and details of a SCR exhaust gas aftertreatment system for a HFO-fueled vessel. The SCR catalyst is placed before the boiler as close to the engine as possible to allow high temperatures at the catalyst for high NOx conversion and to avoid building of ammonium sulfates.

Fig. 2.25 Combined exhaust gas aftertreatment system for a low-speed engine with a SCR and b dry DeSO (DryEGCS) (Picture Couple Systems GmbH)...

Modeling of the Exhaust Gas Aftertreatment System 22.2.1 Total System Simulation... 

The book is aimed primarily at researchers in industry and academia working on exhaust gas aftertreatment systems. Several chapters however provide reference material that will be useful for teaching general courses on catalytic processes for environmental protection, or dedicated courses on the Selective Catalytic Reduction of NOx. 

Mehrdad Ahmadinejad, Maya R. Desai, Timothy C. Watling and Andrew P.E. York, Simulation of Automotive Emission Control Systems Anke Giithenke, Daniel Chatterjee, Michel Weibel, Bemd Krutzsch, Petr Koci, Milos Marek, Isabella Nova and Enrico Tronconi, Current Status of Modeling Lean Exhaust Gas Aftertreatment Catalysts... 

As a consequence, different engine and aftertreatment calibrations are required with respect to the corresponding application. Furthermore, depending on the application and the required emission hmits, different exhaust gas aftertreatment technologies have to be used. Examples are DPF only, SCR only and combined DPF -I- SCR aftertreatment systems. 

Stringent emission limits for EU and US railroads have forced the introduction of exhaust gas aftertreatment for rail diesel engines. While the most complete pollutant reduction could be achieved with a combined particulate filter and SCR system, an alternative way to meet legislation could be through tuning the engine to meet PM emission limits without a particulate filter and use SCR for NOx reduction. 

Chatterjee D, Kocr P, SchmeiBer V, Marek M, Weibel M, Krutzsch B (2010) Modelling of a combined NOx storage and NH3-SCR catalytic system for Diesel exhaust gas aftertreatment. Catalysis Today 151 395-409... 

Exhaust gas catalysts has been widely used since the laimching of the 1970 Clean Air Act in the USA and especially after the introduction of stricter regulations in 1981. At present, one of the fastest growing areas of catalyst-based technology is automotive pollution control. All gasoline-fuelled vehicles sold in the USA, Japan and in the European Community must be equipped with exhaust aftertreatment in order to meet the emission standards. Oxidation catalysts for heavy-duty vehicles have only been used for a short period, but following the tightening emission standards there will be an increased demand for such systems. 

Fig. 2.21 Combined aftertreatment system for a shunting locomotive a DPF -I- SCR installed in one reactor housing, b gas flow (Picture MTU) with A exhaust gas inlet, 1 diesel oxidation catalyst (DOC), 2 diesel particulate filter (DPF), 3 urea solution Injection, 4 SCR catalyst, 5 ammonia slip catalyst (ASC), 6 urea mixing area, B exhaust gas outlet...

---