| 摘要 |
A preceding oxidation catalyst device (21), a diesel particulate filter (DPF) device (22), the turbine (14) of a turbocharger, a preceding NOx selective reduction catalyst device (23), and a subsequent NOx selective reduction catalyst device (24) are disposed in the exhaust system of an internal combustion engine (10) in this order from the exhaust port side, and an ammonia-based solution feeder (25) is disposed on the inlet side or outlet side of the DPF device (22). The NOx selective reduction catalyst of the preceding NOx selective reduction catalyst device (23) is constituted of a catalyst comprising a rare-earth composite oxide, and the NOx selective reduction catalyst of the subsequent NOx selective reduction catalyst device (24) is constituted of a zeolite catalyst. By thus properly disposing the exhaust gas purification units, not only the percentage of NOx removal is improved in wide ranges from low to high temperatures and to high flow rates, but also the temperature of the DPF device (22) is kept high to increase the period and frequency of continuous regeneration, thereby reducing the frequency of forced regeneration of the DPF device (22) and the discharge amount of CO2 that generates during the forced regeneration. |
