Friedrich Wirbeleit

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.

Effects of Direct Water Injection on DI Diesel Engine Combustion

The effects of in-cylinder water injection on a direct injection (DI) Diesel engine were studied using a computational fluid dynamics (CFD) program based on the Kiva-3v code. The spray model is validated against experimental bomb data with good agreement for vapor penetration as a function of time. It was found that liquid penetration increased approximately 35% with 23% of the fuel volume replaced by water, due mostly to the increase in latent heat of vaporization. Engine calculations were compared to experimental results and showed very good agreement with pressure, ignition delay and fuel consumption. Trends for emissions were accurately predicted for both 44% and 86% load conditions. Engine simulations showed that the vaporization of liquid water as well as a local increase in specific heat of the gas around the flame resulted in lower Nitrogen Oxide emissions (NOx) and soot formation rates. Using stratified fuel-water injection increases soot at 86% loads due in part to late injection. Because NOx decreased at all loads, the injection timing can be advanced to minimize fuel consumption and soot.

Emissionsverbesserung an Dieselmotoren mit Direkteinspritzung mittels Einspritzverlaufsformung

Der vorliegende Bericht ist das wissenschaftliche Ergebnis einer Forschungsaufgabe, die von der Forschungsvereinigung Verbrennungskraftmaschinen e.V. (FVV, Frankfurt) gestellt und von der AVL List GmbH bearbeitet wurde. Das wesentliche Ziel des Forschungsvorhabens war es, eine genauere Kenntnis der Zusammenhange zwischen dem Einspritzvorgang einerseits und den Abgasemissionen sowie dem spezifischen Kraftstoffverbrauch andererseits zu gewinnen. Die Durchfuhrung der Arbeiten gliederte sich in drei Abschnitte, namlich in die Adaption des Brennverfahrens, in die Untersuchung verschiedenster Varianten der Einspritzratenformung und schlieslich in die Ausschopfung des Verbesserungspotentials der Einspritzverlaufsformung durch die Hinzufugung der Abgasruckfuhrung.