Method of purifying exhaust gas of an internal combustion engine

摘要

A NOx occluding and reducing catalyst 20 is provided in an exhaust gas passage of an engine to occlude the NOx in the exhaust gas of a lean air-fuel ratio. The engine is provided with an injector for directly injecting the fuel into the combustion chamber, and the fuel fed by a fuel pump into a common rail with pressure is injected. The additive containing a sulfur-solidifying agent that forms a solid sulfate upon the reaction with sulfur in the fuel due to combustion, is injected into the common rail from a tank due to a pump, and is supplied into the combustion chamber through the injector together with the fuel. When the condition of the atmosphere of the NOx occluding and reducing catalyst is the one where the NOx in the exhaust gas is little absorbed, the ECU adjusts the discharge amount of the pump, and decreases the amount of the additive injected into the common rail or interrupts the injection. This decreases the consumption of the sulfur-solidifying agent.