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. Much attention is paid to the durability of the diesel catalysts, since they have to match the long service life of the diesel engines. The deactivation processes which occur and their impact on the catalyst efficiency are explained. The evaluation which was conducted on both model gases and engine test benches with different engine types shows sulfate formation depends on the various oxides tested for washcoat preparation and overall efficiency which can be optimized by choosing appropriate platinum group metals.
Furthermore it was demonstrated that with a precious metal based diesel catalyst attached to a 12 1 DI/TCI prototype engine, US-heavy duty diesel emission regulations for MY 1994 were met.