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The launching of direct injection gasoline engines is currently one of the major challenges for the automotive industry in the European Union. Besides its potential for a notable reduction of fuel consumption, the engine with direct gasoline injection also offers increased power during stoichiometric and stratified operation. These advantages will most probably lead to a significant market potential of the direct injection concept in the near future. In order to meet the increasingly more stringent European emission levels (EURO IV), new strategies for the exhaust gas aftertreatment are required. The most promising technique developed in recent years, especially for NOx conversion in lean exhaust gases, is the so-called NOx storage catalyst.

Diesel particulate mass emissions and their corresponding size distributions have been investigated on a diesel passenger car at steady state conditions using standard filters and a cascade impactor. These tests have been carried out at two different engine operating conditions (2100 rpm, 2.7 and 13.3 kW, respectively) corresponding to low and high exhaust gas temperatures. Two diesel fuels differing in their sulfur content (150 ppm and 2500 ppm S) have been used for these investigations. The particulate size distribution after diesel oxidation catalyst was found to be affected by the sulfur content of the diesel fuel and by the exhaust gas temperature. Interpretations of these results on a mechanistic basis are given. The diesel particulate emission studies have been extended to dynamic vehicle tests.

The paper describes the research work concerning the investigation and optimization of oxidation catalysts for diesel engines, especially for passenger cars and light duty trucks. The investigations carried out both in the laboratory and on the chassis dynamometer with different engine types (DI and IDI as well as natural aspirated and turbocharged) demonstrate the influence of a number of important catalyst design parameters on catalytic converion of soluble particulate content and gaseous emissions (HC, CO and S02) (e.g. precious metal content, washcoat formulation, space velocity, cell density, substrate material, different exhaust gas temperatures, variable oxygen and sulphur dioxide content) with fresh and aged catalysts.