Exhaust emission control device and method of controlling exhaust emission

摘要

A first heat-resistant filter medium is disposed in an exhaust pathway of an internal combustion engine. The first heat-resistant filter medium traps hydrocarbon compounds and carbon-containing particulates included in a flow of exhaust gas in a dispersive manner to bring the respective particulates and hydrocarbon compounds in contact with oxygen included in the exhaust gas. The trapped hydrocarbon compounds and the trapped carbon-containing particulates are subjected to combustion with the exhaust gas having a filter inflow temperature lower than a combustible temperature of the carbon-containing particulates. A second heat-resistant filter medium is further disposed downstream of the first heat-resistant filter medium to trap the remaining carbon-containing particulates, which have not been trapped by the first heat-resistant filter medium but have passed through the first heat-resistant filter medium. This arrangement desirably enhances the reduction rate of the particulates. Since most of the particulates are trapped by the first filter medium, the second filter medium can keep the high reduction rate of the particulates over a long time period.