Experimental Studies and Reactor Modeling for NOx Control in Diesel Engines using NH3 and HNCO

Maruthi  Devarakonda, Pacific Northwest National Laboratory

Urea-SCR catalysts are regarded as the leading NOx aftertreatment technology to meet the 2010 NOx emission standards for on-highway vehicles running on heavy-duty diesel engines. Unfortunately, during low temperature engine operating conditions, urea droplets might not evaporate and thermolyze to form NH3 to reduce NOx in diesel exhaust. Since urea breaks up into NH3 and HNCO, there is a need to understand the reactions of both the species on an SCR catalyst. This talk presents a brief overview of modeling and experimental efforts using both NH¬3 and HNCO species, individually, on a Fe-zeolite monolith core for NOx aftertreatment. A brief overview of the test procedure involving surface isotherm and transient response tests using NH3 is presented, followed by a discussion on system identification and model validation. To investigate the NH3/NOx (alpha) effect on NOx conversion during the transient response tests, the inlet NH3 concentration is varied based on SCR reaction stoichiometry. In the second part of the talk, test procedure to generate HNCO is presented followed by data analysis and a few observations on possible reaction pathways involving NO, NO2, NH¬3 and HNCO species.

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