An
exhaust gas purification
system comprising an
internal combustion engine (10) and an
exhaust pipe (20) connected to an
exhaust manifold (18) of the
internal combustion engine (10), comprising: a catalyst (40) arranged on the
exhaust pipe (20) on a rear side of the
internal combustion engine (10), a catalyst for
selective catalytic reduction on a
diesel particulate filter (SDPF) (60) arranged on the
exhaust pipe (20) on a rear side of the catalyst (40), a
reducing agent injector (50) arranged on the exhaust
pipe (20) between the catalyst (40) and the SDPF (60), the
reducing agent injector (50) injecting a
reducing agent, and a control device (70) which controls an amount of reducing agent injected by the reducing agent
injector (50), wherein the control device (70) calculates an amount of
ammonia leakage, and wherein the control device (70) reduces the amount of reducing agent injection if a temperature change in an interior of the SDPF (60) per unit time is greater than a reference value and a first
NOx amount measured by a second
NOx sensor (82) at a rear end of the SDPF (60) is greater than a
NOx model value, and increases the amount of reducing agent injection if the first NOx amount is smaller than the NOx model value, wherein: the SDPF (60) comprises a plurality of disks (60a, 60b and 60c) in a direction of
exhaust gas flow, each of the plurality of disks (60a, 60b and 60c) having a circular
cell (60a_10) arranged at a center of the respective one of the plurality of disks (60a, 60b and 60c), and one or more cells (60a_1 to 60a_8) having the same cross section and arranged around the circular
cell (60a_10).