| 摘要 |
The invention has an object of exerting favorable NOx reducing effects even at an exhaust temperature lower than in the prior art without trouble, e.g., at startup after long-term engine rest and is directed to an exhaust emission control device wherein a selective reduction catalyst 5 capable of selectively reacting NOx with ammonia even in the presence of oxygen is incorporated in an exhaust pipe 4, urea water 6 as reducing agent being added in the pipe 4 upstream of the reduction catalyst 5 to depurate NOx through reduction. It has an oxidation catalyst 9 arranged in the pipe 4 upstream of an added position of the urea water 6, the oxidation catalyst 9 having a feature of physically adsorbing NOx in the exhaust gas at a temperature lower than a lower active limit temperature of the reduction catalyst 5 and discharging the adsorbed NOx at a temperature higher than a lower active limit temperature of the oxidation catalyst 9, and means (a fuel injection device 14) for adding fuel into the exhaust gas 3 upstream of the oxidation catalyst, start of the fuel addition by the fuel addition means being refrained until exhaust temperature on an inlet side of the reduction catalyst 5 is increased to a preset temperature comparable with the lower active limit temperature of the oxidation catalyst 9. |
