Patent ID: 8028516

Claim:
An exhaust emission purifying apparatus for an engine comprising: an oxidation catalyst disposed in an exhaust system of the engine to oxidize nitrogen monoxide in an exhaust emission by oxidation reaction; a reduction catalyst disposed in the exhaust system to reduce and purify nitrogen oxides in the exhaust emission by using a reducing agent; and reducing agent supply means having an injection nozzle for supplying the reducing agent into the exhaust emission at a position upstream side of the reduction catalyst in an exhaust passage of the exhaust system, wherein the apparatus further comprises: a first pressure sensor disposed at an upstream side of the injection nozzle in the exhaust passage; a second pressure sensor disposed at a downstream side of the reduction catalyst; differential pressure detecting means that detects a differential pressure between a pressure in the exhaust passage on the upstream side of the injection nozzle and a pressure in the exhaust passage on the downstream side of the reduction catalyst; and second determining means for determining that the constituent of the reducing agent has accumulated in the exhaust passage when the differential pressure detected by the differential pressure detecting means becomes equal to or greater than a predetermined pressure.