| 摘要 |
An exhaust gas purification system for an internal combustion engine using an alcohol blended gasoline fuel includes a lean NOx catalyst capable of reducing nitrogen oxides under an oxidizing gas condition and in the presence of hydrocarbons. A bypass conduit is provided with a bypass valve so as to bypass the lean NOx catalyst. Opening of the bypass valve to cause the exhaust gas to flow through the bypass conduit is controlled in accordance with the alcohol concentration of the fuel. When the alcohol concentration 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 at low and medium engine speeds and low and medium engine loads, and the catalyst is utilized at a maximum. On the other hand, when the alcohol concentration 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 at medium engine speeds and medium engine loads, and useless degradation of the lean NOx catalyst is prevented. |
