EXHAUST PURIFICATION DEVICE FOR INTERNAL COMBUSTION ENGINE

摘要

In an internal combustion engine, a NOx selective reduction catalyst (15) is placed in an engine exhaust path and an aqueous urea solution contained in an aqueous urea solution tank (20) is supplied to the NOx selective reduction catalyst (15) to selectively reduce NOx. The aqueous urea solution tank (20) is constructed from a main tank (20a) and a sub-tank (20b) placed in the main tank (20a). The aqueous urea solution in the sub-tank (20b) is delivered to an aqueous urea solution supply valve (17). When the aqueous urea solution tank (20) is to be supplemented with an additional aqueous urea solution, the additional solution is supplied to the sub-tank (20b). A level sensor (40) determines whether or not the aqueous urea solution is added to the aqueous urea solution tank (20), and when it is determined in engine operation immediately after the addition to the aqueous urea solution tank (20) that the NOx purification ratio has decreased to a level lower than or equal to a permissible level, it is determined that the added solution is abnormal.