| 摘要 |
PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of suppressing the exhaust of nitrogen oxide to outside air even when the amount of the nitrogen oxide flowing out of a selective reduction type catalyst device relative to the amount of the nitrogen oxide flowing into the selective reduction type catalyst device cannot be reduced down to a desired amount.SOLUTION: When an SCR outflow NOx amount (an ASC inflow NOx amount) relative to an SCR inflow NOx amount is determined not to be reduced to an increase process performance determination value α (S105:YES), on condition that a catalyst bed temperature (an ASC bed temperature) of an ASC device for oxidizing ammonia flowing out of an SCR device falls within a HC-SCR possible temperature range to enable the ASC device to reduce NOx in exhaust gas with selective catalyst reduction using HC as a reductant, increase processes (S105-108) for increasing the amount of the HC in the exhaust gas flowing into the ASC device through the addition of unburnt fuel to the exhaust gas are performed to further activate the selective catalyst reduction reaction of the NOx in the ASC device.SELECTED DRAWING: Figure 2 |
