Soot distribution in Diesel Particulate Filters under transient driving conditions

摘要

Diesel Particulate Filters have been success fully introduced at large production scale for passenger cars. Diesel filters were used for stationary or city buses applications in the past, using a passive soot regeneration mechanism with quite limited soot combustion rates. A daily maintenance was then required to manually clean any remaining soot not regenerated. With the introduction of the modern engine management systems including the possibility to operate fuel post injection and the development of Silicon Carbide substrates, Diesel Particulate Filters for passenger cars became possible with no need for intensive maintenance (not possible anyway). To avoid filter cracks during uncontrolled soot regeneration events, the maximum soot loading tolerated above which a soot regeneration procedure must be launched is limited to about 8g/L for typical SiC filters and much lower for cordierite filters with relatively low thermal mass. Because soot loading is evaluated using pressure drop measurement across the filter, soot spatial maldistribution in the filter causes local soot concentrations that can exceed these values and can lead to destructive local peak temperatures or high thermal gradients. Soot distribution inside a DPF is conditioned by many complex phenomena such as inlet cone geometry, thermal insulation and driving cycle. Using transient engine dyno and cold flow anemometry measurements, the influence of the parameters listed above have been investigated. The results show that the transient exhaust flow conditions play an important role when investigating soot distribution in filters. The inlet cone geometry does not influence significantly the soot distribution during loading within the experimental conditions of our investigation.