Exhaust gas purifying device for engine

摘要

An exhaust gas purifying device for an engine comprises a catalyst arranged in the exhaust passage for purifying the exhaust gas, the catalyst having an oxidizing ability. An amount of sulfate adsorbed in the catalyst is obtained. When the adsorbed sulfate amount becomes larger than a predetermined amount, a reducing agent is fed to the catalyst temporarily to desorb the adsorbed sulfate from the catalyst and reduce the sulfate. At this time, the amount of the reducing agent is set to make the air-fuel ratio of the exhaust gas flowing into the catalyst rich.