Patent ID: 7500355

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 on an upstream side of the reduction catalyst in an exhaust passage of the exhaust system, wherein the apparatus further comprises: first temperature difference detecting means for detecting a temperature difference between an outer wall temperature of the exhaust passage and an exhaust emission temperature at a portion to which the reducing agent supplied from the injection nozzle adheres; second temperature difference detecting means for detecting a temperature difference between an outer wall temperature of the exhaust passage and an exhaust emission temperature at a portion to which the reducing agent does not adhere; and first determining means for determining that a constituent of the reducing agent has accumulated in the exhaust passage when the temperature difference detected by the first temperature difference detecting means becomes greater than the temperature difference detected by the second temperature difference detecting means by a value equal to or greater than a predetermined value.