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Stringent standards for the emission of particulate matter by heavy duty diesel engines will come into effect in the nineties in the US and are anticipated to come into effect in the same period in W-Europe and in Japan. This has lead most of the manufacturers to intensify the evaluation of exhaust aftertreatment devices. Although particulate filtering systems proved to be valuable in limited fleet applications, the general introduction did not take place because of complicated and limited durability regeneration. Flow-through catalysts which were introduced for passenger cars in 1989 drew a lot of attention for potential heavy duty diesel applications. In this paper the major parameters affecting the performance of these flow-through catalysts and the particularities related to heavy duty diesel application are outlined. The parameters deal with the fuel sulfur content, the test cycles applied, the catalyst formulation and washcoat composition.

After a review of the current status of development of heavy-duty direct injection diesel engines (all turbocharged and intercooled) technologies to meet US-EPA 1994 heavy-duty diesel emission standards are discussed. Special attention is given to the NOx-particulate trade-off and to the various particulate fractions (carbon, lube oil, sulfates), and to measures for their reduction by internal means. A major part of the paper addresses the application of oxidation catalysts as a very efficient and cost-effective aftertreatment device to burn off soluble particulate fractions, CO, HC, odorants and PAH. The paper concludes with an outlook on foreseeable developments of the heavy-duty diesel in the future.