| 摘要 |
PROBLEM TO BE SOLVED: To improve the efficiency of reducing NOx in a high temperature range of exhaust gas.SOLUTION: A first selective reduction type catalyst 21 composed of a silver-based catalyst is provided in an exhaust pipe 16 of an engine 11, and a second selective reduction type catalyst 22 composed of a copper-based catalyst, an iron-based catalyst, or a vanadium-based catalyst is provided in an exhaust pipe 16 on an exhaust gas downstream side than the first selective reduction type catalyst 21. A liquid injection nozzle 26 capable of injecting hydrocarbon-based liquid 24 toward the first selective reduction type catalyst 21 is provided in the exhaust pipe 16 on the exhaust gas upstream side than the first selective reduction type catalyst 21, and a hydrocarbon-based liquid supplying means 27 is configured to supply the liquid 24 via a liquid injection amount regulating valve 31 to the liquid injection nozzle 26. The temperature of exhaust gas related to the first selective reduction type catalyst 21 is detected by a first temperature sensor 41, and a controller 38 is configured to control the liquid injection amount regulating valve 31 based on detection output of the first temperature sensor 41. |
