Exhaust emission purification system for diesel engine

摘要

In addition to the first exhaust emission purification device (12) arranged in an exhaust passage of the engine, having the first continuously regenerating type DPF (12A) and the first SCR catalyst (12B), in the bypass exhaust passage (101) there is provided the second exhaust emission purification device (13) having the second continuously regenerating type DPF (13A) and the second SCR catalyst (13B) to constitute the exhaust emission purification system for the diesel engine. In addition, when the exhaust gas temperature is within the low-temperature region lower than the predetermined temperature region, the exhaust gas temperature is raised, and after the exhaust gas is caused to pass through the second exhaust emission purification device (13), control is made so as to pass through the first exhaust emission purification device (12). Thereby, even in an engine operating state at low exhaust gas temperature such as during idling and during an operation at low load, not only PM but also Nox can efficiently be cleaned up, and it is possible to exhibit excellent exhaust gas cleanup performance in the wide engine operating region. IMAGE