EXHAUST GAS PURIFICATION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE

The present invention discloses an exhaust gas purification system for an internal combustion engine, which is provided with: a selective reduction type catalyst arranged in an exhaust passage of the internal combustion engine; a low pressure EGR mechanism that is equipped with a low pressure EGR passage for introducing a part of an exhaust gas flowing through a portion of the exhaust passage downstream of a turbine of a centrifugal supercharger to a portion of an intake passage upstream of a compressor as a low pressure EGR gas, and a low pressure EGR valve for changing a channel cross section of the low pressure EGR passage; a supply device for supplying an ammonia derived compound to the selective reduction type catalyst; and a control means for controlling the supply of the ammonia derived compound by the supply device; wherein the supply device is arranged in such a manner that the ammonia derived compound can be supplied into a portion of the exhaust passage upstream of a connection portion of the low pressure EGR passage. The control means causes the supply device to supply the ammonia derived compound when the low pressure EGR valve is in a valve open state, whereby condensed water and evaporated substances thereof existing in a path of the low pressure EGR gas are neutralized with the ammonia derived compound.