| abstract |
Provided is an exhaust purification device capable of simultaneously purifying PM and NOx in exhaust gas, preventing thermal degradation of the SCR catalyst, and achieving low temperature activity of the SCR catalyst. When the exhaust gas is hot, a butterfly valve 25 is opened, and a part of the high-temperature exhaust gas downstream of the DPF 31 passes through a bypass passage 23. On the other hand, the oxidation catalyst 35 is close to the outside air temperature before the butterfly valve is opened. The oxidation catalyst 35 has a heat capacity. When the high-temperature exhaust gas passes through the oxidation catalyst 35, a part of the heat quantity of the high-temperature exhaust gas is absorbed by the oxidation catalyst 35, and the high-temperature exhaust gas cools down. Thereby, high temperature exhaust is prevented from flowing into the SCR catalyst 33, and thermal degradation of the SCR catalyst is prevented. When the exhaust temperature is low, the butterfly valve 25 is opened, and a part of the exhaust passes through the bypass passage 23. At this time, due to oxidation by the oxidation catalyst 35, NO decreases, NO2 increases, and the NO2 / NO molar ratio increases. The SCR catalyst 33 is activated by setting the molar ratio to around 1. [Selection] Figure 1 |