EXHAUST GAS PURIFICATION APPARATUS IN AN INTERNAL COMBUSTION ENGINE

摘要

An apparatus that raises temperature of a post-catalyst at an early time while suppressing reducing agent poisoning of the post-catalyst and discharge of a reducing agent into the outside when a pre-catalyst and the post-catalyst are arranged in series in an exhaust passage of an internal combustion engine in order from an upstream side thereof. The pre-catalyst is arranged to allow an exhaust gas to flow between an outer peripheral surface thereof and an inner peripheral surface of the exhaust passage. A reducing agent addition valve adding a reducing agent to allow the reducing agent to pass through the pre-catalyst is arranged immediately upstream of the pre-catalyst in the exhaust passage. Further, a retention catalyst is arranged in the exhaust passage between the pre-catalyst and the post-catalyst, to temporarily retain the reducing agent in the exhaust gas.