Device for purifying exhaust gas of engine

Abstract

A device for purifying the exhaust gas of an engine having a plurality of cylinders divided into first and second cylinder groups, the first and the second cylinder groups being connected to first and second exhaust passage, respectively, and performing a lean operation, comprises an NH.sub.3 synthesizing catalyst arranged in the first exhaust passage, and an exhaust gas purifying catalyst arranged in an interconnecting passage, which interconnects the first passage downstream of the NH.sub.3 synthesizing catalyst and the second exhaust passage, for purifying the inflowing NO.sub.X and NH.sub.3. An additional engine performing a rich operation is provided and the exhaust gas thereof is fed to the first exhaust gas passage upstream of the NH.sub.3 synthesizing catalyst to make the exhaust gas air-fuel ratio of the exhaust gas flowing into the NH.sub.3 synthesizing catalyst rich, to thereby synthesize NH.sub.3 therein. An amount of NH.sub.3 or NO.sub.X flowing into the exhaust gas purifying catalyst is obtained, and the additional engine is controlled in accordance with the obtained NH.sub.3 or NO.sub.X amount to control the amount of the reducing agent flowing to the exhaust gas purifying catalyst.