Patent ID: 7703276

Claim:
An exhaust gas purifying apparatus for an engine comprising: a reduction catalyst which is arranged in an exhaust system of the engine, for reducing and purifying nitrogen oxide in an exhaust gas using a reducing agent; reducing agent supply means having an injection nozzle which is supplied with a reducing agent together with compressed air and atomizes said reducing agent, and which injection-supplies this to an exhaust gas on an upstream side of said reduction catalyst inside an exhaust gas passage of said exhaust system; and temperature detection means which is provided in the vicinity of said injection nozzle on the upstream side in the exhaust gas passage, and which detects the exhaust gas temperature inside said exhaust gas passage; wherein said reducing agent supply means uses a detection signal of the exhaust gas temperature from said temperature detection means to set, for that exhaust gas temperature, a supply quantity of reducing agent and compressed air at or above a lower limit for cooling the interior of said injection nozzle to below a temperature at which the reducing agent crystallizes, and supplies reducing agent and compressed air to said injection nozzle.