| 摘要 |
A previous-stage oxidation catalyst device (21), a DPF device (22), a turbine (14) of a turbocharger, a previous-stage NOx selective reduction catalyst device (23), and a subsequent-stage NOx selective reduction catalyst device (24) are disposed in the exhaust system of an internal combustion engine (10) in this order from an exhaust port side. An ammonia-based solution feeder (25) is disposed on an inlet side or outlet side of the DPF device (22). The NOx selective reduction catalyst of the previous-stage NOx selective reduction catalyst device (23) is made of a catalyst containing a rare earth composite oxide, and the NOx selective reduction catalyst of the subsequent-stage NOx selective reduction catalyst device (24) is made of a zeolite catalyst. By thus properly disposing the exhaust gas purification units, the NOx removal rate is improved in wide ranges from low to high temperatures and to high flow rates, and also the temperature of the DPF device (22) is kept high to increase the time and frequency of continuous regeneration, thereby reducing the frequency of forced regeneration of the DPF device (22) and the amount of discharge of CO 2 produced during the forced regeneration. |
