| abstract |
An exhaust gas purification system (1) comprises a DPF device (13) and a selective catalytic reduction-type catalytic device (an SCR catalytic device) (14) provided in that order, in an exhaust passage (12) in an internal combustion engine (11), from the upstream side of the exhaust passage (12). During normal operation, the NOx emission is computed from an NOx emission map for normal operation, while during forced regeneration of the DPF device (13), the NOx emission is computed from an NOx emission map for forced regeneration. The amount of an aqueous ammonia solution (S) corresponding to the computed NOx emission supplied is computed. The aqueous ammonia solution (S) is supplied into an exhaust gas (G) on the upstream side of the selective catalytic reduction-type catalytic device (14) so that the amount supplied is brought to the computed amount supplied. According to the above constitution, not only during the normal operation but also during the forced regeneration of the DPF device (13), a proper amount of a reducing agent can be supplied, and the emission of NOx and ammonia toward the downstream side of the selective catalytic reduction-type catalytic device (14) can be suppressed. |