EXHAUST GAS PURIFICATION SYSTEM FOR INTERNAL COMBUSTION ENGINES USING GASOLINE-ALCOHOL MIXTURE AS A FUEL.

摘要

An exhaust gas purification system for an internal combustion engine using an alcohol blended gasoline fuel includes a lean NOx catalyst (2) capable of reducing nitrogen oxides under an oxidizing gas condition and in the presence of hydrocarbons. A bypass conduit (3) is provided with a bypass valve (4) so as to bypass the lean NOx catalyst (2). Opening of the bypass valve (4) to cause the exhaust gas to flow through the bypass conduit (3) is controlled in accordance with the alcohol concentration of the fuel. When the alcohol concentration (CAL) is low, the bypass valve opening range is limited to a high engine speed and high engine load range, so that the exhaust gas is caused to flow through the lean NOx catalyst (2) at low and medium engine speeds and low and medium engine loads, and the catalyst (2) is utilized at a maximum. On the other hand, when the alcohol concentration (CAL) is high, the bypass valve opening range is determined so as to include a medium to high engine speed and medium to high engine load range, so that the exhaust gas is caused to flow through the bypass conduit (3) at medium engine speeds and medium engine loads, and useless degradation of the lean NOx catalyst (2) is prevented. IMAGE