| 摘要 |
PURPOSE: A system for purifying exhaust gas is provided to prevent the clogging phenomenon of a spraying tip and a supplying line by returning a urea solution from the spraying tip and the supplying line to a urea tank after an engine is turned off. CONSTITUTION: An urea tank(150) is prepared. A dosing module(120) sprays urea to an exhaust gas line. A selective catalytic reduction unit purifies nitrogen oxide using the urea from the dosing module. When an engine is turned off, the urea is returned from the dosing module to the urea tank using a reverting valve. A controlling part controls the reverting valve and the dosing module according to the operational condition of the engine.
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