Abgasreinigungsverfahren für einen Motor

摘要

An exhaust gas purifying device for an engine (1) comprises an exhaust gas purifying catalyst (19) arranged in the exhaust passage. The catalyst is capable of reducing NOX in the catalyst in the oxidizing atmosphere, and comprises a reducing agent adsorbent adsorbing a reducing agent in the inflowing exhaust gas therein when the pressure in the adsorbent becomes higher, and desorbing the adsorbed reducing agent therefrom when the pressure in the adsorbent becomes lower. An exhaust gas control valve (23) is disposed in the exhaust passage downstream of the catalyst. When both the engine load and the engine speed are low, the opening of the valve is made smaller to increase the pressure in the catalyst. At this time, hydrocarbon is fed to the catalyst, and is then adsorbed in the catalyst. When the engine load or the engine speed becomes high, or the cumulative amount of hydrocarbon fed to the catalyst becomes larger than a predetermined amount, the valve is made fully open to reduce the pressure in the catalyst. At this time, the adsorbed hydrocarbon is desorbed from the catalyst, and then reduces NOX in the catalyst.