부산대학교 도서관

An exhaust emission control system, which comprises control means 8 operable, in response to satisfaction of a given stop condition, to automatically stop an engine, and subsequently, in response to satisfaction of a given restart condition, to automatically restart the automatically stopped engine, a flow passage 6 adapted for an aqueous urea solution for reducing nitrogen oxides contained in exhaust gas of the engine, and supply/recovery means 7 adapted to drive a pump 10 to supply an aqueous urea solution to the flow passage and recover an aqueous urea solution from the flow passage. The control means is operable, when the engine is forcibly stopped by turning off an ignition switch, to instruct the supply/recovery means 7 to recover an aqueous urea solution from the flow passage 6, and, when automatically stopping the engine in response to satisfaction of the given stop condition, to prohibit the supply/recovery means 7 from recovering an aqueous urea solution from the flow passage 6.