| 摘要 |
An upstream catalyst (12) which stores oxygen in exhaust gas and releases the stored oxygen for oxidizing a reducing agent component contained in the exhaust gas, and a downstream catalyst (13) which stores nitrogen oxides in the exhaust gas and releases the stored nitrogen oxides by reducing the stored nitrogen oxides by the reducing agent component contained in the exhaust gas, are provided in an exhaust passage (11) of an engine (2). When the storage amount of nitrogen oxides of the downstream catalyst (13) reaches a predetermined value, additional fuel is injected from a fuel injector (7) after combustion, and stored oxygen in the upstream catalyst (12) is released by the reducing agent components in the additional fuel. After release of oxygen, the supply of the additional fuel is stopped and the supply of the main fuel is increased. |
