Patent attributes
An exhaust gas purification system (1) comprises a DPF device (13) and a selective catalytic reduction type catalytic device (SCR catalytic device) (14) provided, in that order, from the upstream side of an exhaust passage (12) of an internal combustion engine (11). During ordinary operation, a NOx emission amount is calculated from a NOx emission map for ordinary operation, while during forced regeneration of the DPF device (13), a NOx emission amount is calculated from a NOx emission map for forced regeneration. A supply amount of aqueous ammonia solution (S) corresponding to the calculated NOx emission amount is then calculated. The aqueous ammonia solution (S) is then supplied into an exhaust gas (G) at the upstream side of the selective catalytic reduction type catalytic device (14) such that the amount supplied is brought to the calculated supply amount. As a result of this configuration, appropriate amounts of reducing agent can be supplied not only during ordinary operation but also during the forced regeneration of the DPF device (13), and the emission of NOx and ammonia downstream to the selective catalytic reduction type catalytic device (14) can be suppressed.
