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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.

The performance of two catalyst preparations, styled base and base/noble, were determined employing a simulated mining vehicle loading cycle. Such cycles are characterized by sufficiently high exhaust temperatures to cause auto-regeneration of the filter units when these catalyst preparations are employed. Such loading is exhibited in raining service by some moderate and most high production load-haul-dump vehicles plus some haulage trucks. These preparations were shown to be capable of depressing the nominal, ‘untreated’ steady-state minimum soot ignition temperature of approximately 500°C (932°F), to a range varying from 395°C to 424°C (743°F to 797°F). Results of gaseous constituent analyses, particulate determinations, polynuclear aromatic hydrocarbon sampling, catalytic sulphur conversion (SO2 to H2SO4) and Ames testing are presented for the two catalyst preparations studied.