EXHAUST EMISSION CONTROL SYSTEM

摘要

PROBLEM TO BE SOLVED: To provide an exhaust emission control system capable of efficiently controlling NOx in an excessive oxygen area exhausted from an internal combustion engine and of efficiently controlling CO.HC even if exhaust gas is in a low-temperature range. SOLUTION: In the upstream of an exhaust gas passage in the internal combustion engine, there is disposed an exhaust gas component concentration controlling means of controlling carbon monooxide and hydrogen in exhaust gas and the ratio of hydrogen/carbon monooxide concentration ratio when air-fuel ratio is rich or a stoichiometric air amount. In the downstream of the exhaust gas passage, there is disposed an NOx adsorption reduction catalyst of adsorbing nitrogen oxides when the air-fuel ratio is lean and reducing the adsorbed nitrogen oxides to nitrogen when the air-fuel ratio is rich or the stoichiometric air amount.