In order to reduce emissions from diesel engines, an aftertreatment systems that combines DPF and urea SCR was applied in this study. the following findings were obtained by conducting experimental studies on how to improve the NOx reduction efficiency of the urea SCR system at low exhaust gas temperature conditions: (1) NH3 plays the role of a reductant for NOx in the SCR catalyst. The urea conversion rate to NH3 through pyrolysis in the gas phase upstream of the SCR catalyst is not dominant even in high exhaust gas temperature conditions. NH3 is mainly generated through pyrolysis and hydrolysis reactions in the SCR catalyst. (2) Reductant including NH3 is adsorbed in the SCR catalyst. The maximum reductant adsorption quantity in the SCR catalyst is significantly increased when the exhaust gas temperature at the SCR inlet is low. (3) When the temperature at the SCR inlet becomes lower than 300 deg C, the lower the temperature, the worse the NOx reduction efficiency becomes, which are conventionally known characteristics. It was made clear that NOx reduction efficiency is improved significantly by increasing the reductant adsorption quantity even thought the exhaust gas temperature at the SCR inlet is low. (4) In conditions where the SCR inlet gas temperature is high, reductant adsorption in the catalyst cannot be expected. Due to a high reduction reaction rate because of the high exhaust gas temperature, high NOx reduction efficiency can be achieved through real time urea solution injections. (5) In order to control the reductant adsorption quantity in the SCR caralysts, control logic was bulit to make judgments on the timing of urea solution injections. Through conducting the JE05 mode test applying the controls, 75% NOx reduction efficiency was achieved even with a low SCR inlet exhaust gas temperature of 158 deg C (mode average), in conditions that had a mode-overall NO2/NOx ratio of 0.57 at the inlet of the SCR catalyst. This emission level is close to the Post New Long-term regulation values, which will come into effect in 2009 in Japan. (6) In this study, a DOC and catalyzed DPF were installed upstream of the SCR to increase the NO2/NOx ratio at the SCR inlet. By applying NH3 adsorption quantity controls, improved effects on NO reduction efficiency, especially during acceleration, were clearly seen. It is considered that the formation of ammonium nitrate on the SCR catalyst generated from NO2 and NH3 at low temperature conditions contributed to reducing the NO that was flowing into the SCR catalysts at increasing speed.


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    Titel :

    A study on the improvement of NO(x) reduction efficiency for a urea SCR system (first report) - a concept of NH3 adsorption quantity control and its application with transient operation


    Weitere Titelangaben:

    Untersuchung der NOx-Minderung für ein Harnstoff-SCR-System (erster Bericht) - Regelungskonzeption der NH3-Adsorptionsmenge und deren Anwendung beim transienten Betrieb


    Beteiligte:
    Murata, Yutaka (Autor:in) / Tokui, Sadahito (Autor:in) / Watanabe, Soichiro (Autor:in) / Takeshita, Kiyoto (Autor:in) / Daisho, Yasuhiro (Autor:in) / Suzuki, Hisakazu (Autor:in) / Ishii, Hajime (Autor:in)

    Erschienen in:

    Erscheinungsdatum :

    2009


    Format / Umfang :

    8 Seiten, 12 Bilder, 3 Tabellen, 6 Quellen



    Medientyp :

    Aufsatz (Zeitschrift)


    Format :

    Print


    Sprache :

    Englisch





    Improvement of NOx Reduction Rate of Urea-SCR System by NH3 Adsorption Quantity Control

    Ishii, Hajime / Suzuki, Hisakazu / Tokui, Sadahito et al. | SAE Technical Papers | 2008


    Improvement of NOx reduction rate of urea-SCR system by NH3 adsorption quantity control

    Murata,Y. / Tokui,S. / Watanabe,S. et al. | Kraftfahrwesen | 2008


    Improvement of NOx Reduction Rate of Urea-SCR System by NH~3 Adsorption Quantity Control

    Murata, Y. / Tokui, S. / Watanabe, S. et al. | British Library Conference Proceedings | 2008