Günter Wenninger

Removal of nitrogen oxides from the exhaust of a lean-tune gasoline engine

There is an increasing interest in running passenger car engines lean of the stoichiometric air to fuel ratio (A/F) to improve fuel economy. One method being considered by vehicle manufacturers is to operate lean A/F (excess air) during cruising and return to stoichiometric operation when more power is required. The challenge for the catalyst manufacturer is to supply a product for this vehicle which will reduce NOx emissions from both lean and stoichiometric operating points to below probable EC tier III legislative limits. A technique has been developed where NOx is stored on an adsorbing catalyst while the engine runs lean. Upon switching to a short rich biased stoichiometric excursion the adsorbed NOx is released and reduced by precious metal components on the catalytic system. Selected adsorber catalysts were tested on both simulated exhaust gas and a standard bench engine with secondary air injection. The results suggest an adsorbing process whereby NO is oxidized to NO2 on Pt under lean conditions and the latter is subsequently adsorbed on an adsorbent material as a surface nitrate species. Upon return to a stoichiometric A/F ratio this species decomposes and NOx is released and subsequently reduced. The adsorber was also tested on a bench prototype lean tune engine. The results indicate an averaged NOx conversion of more than 90% over a test cycle in which the A/F ratio is cycled between lean operation and a rich biased stoichiometry.

Optitimierurung der Selektiven Katalalytischen Reduktion mittels numerischer Methoden

Zur Absenkung der Stickoxidemissionen von Dieselmotoren wird derzeit haufig die Selektive Katalytische Reduktion (SCR) mit Ammoniak als Reduktionsmittel eingesetzt. Die Aufbereitung der als Ammoniak-Vorlaufersubstanz eingesetzten Harnstoff-WasserLosung umfasst zahlreiche Teilprozesse, die fur die Auslegung der Abgasanlage vollstandig verstanden werden mussen. Im Rahmen einer Kooperation der Daimler AG mit dem Institut fur Fahrzeugantriebe und Automobiltechnik (IFA) der Technischen Universitat Wien wurde insbesondere die CFD-Simulation erfolgreich zur Losung dieser Aufgabe eingesetzt.

Optimization of the selective catalytic reduction by means of numerical methods

At present the Selective Catalytic Reduction (SCR) with ammonia as reducing agent is frequently used for Diesel powered vehicles to decrease significantly the nitric oxide (NOx) emissions. The preparation of ammonia includes numerous sub-processes that need to be understood completely to develop exhaust gas systems efficiently. Within a co-operation project between Daimler AG and the Institute for Powertrains and Automotive Technology (IPA) of the Vienna University of Technology especially the CFD simulation method was employed successfully to solve this task.