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Low Emission Gasoline Engine - After Treatment Systems in View of Eec Phase Iii Limits
Published March 16, 1994 by Associazione Tecnica Dell'Automobile in Italy
European emission standards will closely match, by the end of the century, California LEV / ULEV standards. Although still under evaluation, the German MVEG and European Parliament proposals indicate that engine - after treatment technologies are expected to substantially step up in effectiveness. HC and NOx emission levels will have to be reduced by approximately 80% in the next five years, and CO emissions roughly halved. It is likely that CO2 emission restrictions will be imposed, requiring tight control of fuel consumption. This goal must be pursued primarily by developing innovative after treatment technologies apt to reduce cold start emissions to a minimum (e.g. electrically heated catalysts, close-coupled catalysts, secondary air injection). However, it is necessary to proceed in parallel by revising and refining engine control for optimum engine out emissions from the point of view of the after treatment system. Optimized mixture preparation may substantially improve in-cylinder A/F ratio control both under cold start conditions and transient operation. Optimized A/F control strategies may improve catalyst performance under transient conditions, and significantly increase the useful lifetime of the catalyst. In addition to these main work areas, continuing support must be ensured in the field of catalyst formulation (loading and volume optimization for durability), and prediction/testing methodologies (converter modeling, engine dynamometer testing of catalyst and engine/converter performance and accelerated ageing cycle definition).