EXHAUST EMISSION CONTROL SYSTEM

摘要

PROBLEM TO BE SOLVED: To reduce NOx emission to zero as much as possible, which is generated abruptly during a transient period when an internal combustion engine is operated with a stoichiometric air-fuel ratio. SOLUTION: A NOx adsorption catalyst is disposed in an exhaust gas passage. When an engine is operated with a stoichiometric air-fuel ratio, a ratio is set by control to be slightly richer than the stoichiometric air-fuel ratio (an excess air ratioλranging from 0.97 to 1). Accordingly, since NOx generated abruptly during a transient period, when the engine is operated with the stoichiometric air-fuel ratio, is adsorbed and reduced by the NOx adsorption catalyst efficiently, an amount of NOx emission is reduced significantly.