Patent ID: 8904765

Claim:
An internal combustion engine, comprising: an ammonia feeder which feeds ammonia to a combustion chamber, an upstream side NO x selective reduction catalyst which is arranged in an engine exhaust passage and which selectively reduces NO x by a feed of a reducing agent constituted by ammonia, and a downstream side NO x selective reduction catalyst which is arranged downstream of the upstream side NO x selective reduction catalyst in the engine exhaust passage and which selectively reduces NO x by the feed of the reducing agent constituted by ammonia, the engine performing combustion so that an air-fuel ratio at the time of combustion becomes lean, wherein the upstream side NO x selective reduction catalyst has a first region operating state where a NO x removal rate rises when a ratio of concentration of ammonia to NO x of an inflowing exhaust rises and a second region operating state where the NO x removal rate becomes substantially constant when a ratio of concentration of ammonia to NO x of the inflowing exhaust rises, the downstream side NO x selective reduction catalyst has an ammonia oxidation ability which is larger than the upstream side NO x selective reduction catalyst, and an electronic controller configured to maintain a ratio of concentration of ammonia to NO x of the exhaust which flows into the upstream side NO x selective reduction catalyst in the second region operating state.