INTERNAL COMBUSTION ENGINE AND CONTROL SYSTEM

Exhaust gas discharged from a combustion chamber (20) flows through an exhaust flow path (42) of an internal combustion engine (1). A reducing agent supply unit supplies a reducing agent to the exhaust flow path (42) via a nozzle (61) attached to the exhaust flow path (42) and the reducing agent is mixed with the exhaust gas. A reactor (66) performs denitration treatment by bringing the exhaust gas flowing in from the exhaust flow path (42) into contact with a catalyst. The exhaust gas passing through the reactor (66) is directed to a flue (81). A bypass flow path (681) bypasses the reactor (66) and connects the exhaust flow path (42) and the flue (81). A bypass valve (682) opens and closes the bypass flow path (681). The supply control unit controls the reducing agent supply unit to stopsupplying the reducing agent to the exhaust flow path (42) when the valve opening process of the bypass valve (682) is detected. As a result, the inflow of the reducing agent to the downstream side ofthe reactor (66) can be s