Exhaust gas purification method and exhaust gas purification system

Abstract

In an exhaust gas purification system () for conducting control of raising temperature of a DPF () by supplying an unburned fuel to an upstream side of an oxidation catalyst to oxidize it, a minimum value (Qumin) of a first upper limit value (Qu) acquired by subtracting a fuel injection amount (Qe) for in-cylinder combustion from a first combustible fuel amount (Qa) limited by an air/fuel ratio, a second upper limit value (Qu) acquired by subtracting the fuel injection amount (Qe) for in-cylinder combustion from a second combustible fuel amount (Qa) limited by an atmospheric pressure, and a third upper limit value (Qu), which is a third combustible fuel amount (Qa) which can be oxidized by the oxidation catalyst limited by a catalyst temperature index temperature (Tg, Tg) and an engine speed (Ne) is set as an upper limit value (Qu) for the unburned fuel supply amount (Qp). By this arrangement, at forced regeneration of the DPF (), the unburned fuel supplied into an exhaust gas is surely oxidized and generation of white smoke is prevented regardless of an operation state of an internal combustion engine ().