EXHAUST GAS PURIFICATION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE USING ALCOHOL BLENDED GASOLINE FOR FUEL

摘要

ABSTRACT OF THE DISCLOSUREAn exhaust gas purification system for an internalcombustion engine using an alcohol blended gasoline fuelincludes a lean NOx catalyst capable of reducing nitrogenoxides under an oxidizing gas condition and in the presenceof hydrocarbons. A bypass conduit is provided with a bypassvalve so as to bypass the lean NOx catalyst. Opening of thebypass valve to cause the exhaust gas to flow through thebypass conduit is controlled in accordance with the alcoholconcentration of the fuel. When the alcohol concentrationis low, the bypass valve opening range is limited to a highengine speed and high engine load range, so that the exhaustgas is caused to flow through the lean NOx catalyst at lowand medium engine speeds and low and medium engine loads,and the catalyst is utilized at a maximum. On the otherhand, when the alcohol concentration is high, the bypassvalve opening range is determined so as to include a mediumto high engine speed and medium to high engine load range,so that the exhaust gas is caused to flow through the bypassconduit at medium engine speeds and medium engine loads, anduseless degradation of the lean NOx catalyst is prevented.