EXHAUST EMISSION CONTROL SYSTEM FOR INTERNAL COMBUSTION ENGINE (AS AMENDED)

摘要

An object of the present invention is to increase the NOx purification rate of an unactivated SCR catalyst in an exhaust emission control system for an internal combustion engine that has an oxidation catalyst and the SCR catalyst disposed downstream of the oxidation catalyst. In order to achieve this object, the present invention provides an exhaust emission control system for an internal combustion engine, including an oxidation catalyst disposed in an exhaust passage of the internal combustion engine, an SCR catalyst that is disposed downstream of the oxidation catalyst in the exhaust passage, and a supply device for supplying unburnt fuel to the oxidation catalyst when the SCR catalyst is not yet activated, wherein the amount of NO2 that flows into the SCR catalyst is increased by reducing the amount of unburnt fuel supplied, when a low-load operation of the internal combustion engine is performed.

主权项

1. An exhaust emission control system for an internal combustion engine, comprising:
an oxidation catalyst disposed in an exhaust passage of the internal combustion engine; a selective reduction catalyst that is disposed downstream of the oxidation catalyst in the exhaust passage; temperature increasing unit for increasing a temperature of exhaust flowing out of the oxidation catalyst by supplying unburnt fuel to the oxidation catalyst, when the oxidation catalyst is activated but the selective reduction catalyst is not activated; and control unit for reducing the amount of unburnt fuel to be supplied to the oxidation catalyst by the temperature increasing unit, when a low-load operation of the internal combustion engine is performed during a period in which the unburnt fuel is supplied to the oxidation catalyst by the temperature increasing unit.