Patent ID: 7614213

Claim:
An engine exhaust emission purification apparatus comprising: a reduction catalytic converter disposed in an engine exhaust system to reduce and purify nitrogen oxides by using a liquid reducing agent; an injection nozzle that supplies by injection the liquid reducing agent to a flow of an exhaust emission upstream from the reduction catalytic converter; a nozzle temperature detecting device for detecting a nozzle temperature of the injection nozzle; a temperature maintenance device for maintaining a temperature of at least a part of a liquid reducing agent supply system including the injection nozzle and piping of the injection nozzle at a temperature lower than a boiling point of a solvent of the liquid reducing agent or equal to or higher than a melting point of dissolved matter, wherein the temperature maintenance device is arranged to route a conduit of engine coolant to a flange for attaching the injection nozzle to the exhaust system to thereby cause heat exchange between the flange and the engine coolant; a coolant temperature detecting device for detecting a coolant temperature of the engine coolant; and a circulation control device for controlling circulation or interception of the engine coolant in the conduit, wherein the circulation control device circulates the engine coolant when the detected nozzle temperature is equal to or higher than the boiling point of the solvent of the liquid reducing agent or lower than the melting point of the dissolved matter, and wherein the circulation control device prohibits a circulative flow of the engine coolant when the detected coolant temperature is equal to or higher than the boiling point of the solvent of the liquid reducing agent.