| 主权项 |
1. An internal combustion engine, comprising:
an ammonia feeder which feeds ammonia to a combustion chamber, an upstream side NOx selective reduction catalyst which is arranged in an engine exhaust passage and which selectively reduces NOx by a feed of a reducing agent constituted by ammonia, and a downstream side NOx selective reduction catalyst which is arranged downstream of the upstream side NOx selective reduction catalyst in the engine exhaust passage and which selectively reduces NOx 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 NOx selective reduction catalyst has a first region operating state where a NOx removal rate rises when a ratio of concentration of ammonia to NOx of an inflowing exhaust rises and a second region operating state where the NOx removal rate becomes substantially constant when a ratio of concentration of ammonia to NOx of the inflowing exhaust rises, the downstream side NOx selective reduction catalyst has an ammonia oxidation ability which is larger than the upstream side NOx selective reduction catalyst, and an electronic controller configured to maintain a ratio of concentration of ammonia to NOx of the exhaust which flows into the upstream side NOx selective reduction catalyst in the second region operating state. |
