Exhaust gas purifying system

摘要

An exhaust gas purifying system for an internal combustion engine mounted on an automotive vehicle. The exhaust gas purifying system comprises an exhaust gas component concentration regulating device disposed in an exhaust gas passageway of the engine, for regulating concentrations of gas components in exhaust gas discharged from the engine such that the concentrations of carbon monoxide and hydrogen are respectively not more than 2.0 % by volume and not less than 0.5 by volume and such that a volume concentration ratio of Ähydrogen / carbon monoxideÜ is not smaller than 0.5, in a first exhaust gas condition in which air/fuel ratio of exhaust gas is within a range of from a rich value and a stoichiometric value. Additionally, a NOx adsorbing and reducing catalyst is disposed in the exhaust gas passageway downstream of the exhaust gas component concentration regulating device, for adsorbing nitrogen oxides in a second exhaust gas condition in which the air/fuel ratio of exhaust gas is at a lean value, and reducing the nitrogen oxides into nitrogen in the first exhaust gas condition.