| 摘要 |
PROBLEM TO BE SOLVED: To purify the exhaust gas by effectively utilizing the NOx adsorbing capacity of a trap component with a noble metal supported only in ceria (CeO2) or zeolite. SOLUTION: A low-temperature NOx trap catalyst 14 comprising the trap component or zeolite for trapping NOx when the temperature is lower than a prescribed value is disposed on the downstream side of an exhaust gas cleaning catalyst 13 mounted in an exhaust passage 12 of the engine 1. The length of the exhaust passage 12 to the low-temperature NOx trap catalyst 14 is set so that the low-temperature NOx trap catalyst 14 is maintained at a prescribed temperature or lower than that when the exhaust gas cleaning catalyst 13 is at the active temperature or lower, or while the engine 1 is operated. The low-temperature NOx trap catalyst 14 is dehydrated by detecting the quantity of water absorbed in the low-temperature NOx trap catalyst 14 and increasing the temperature of the exhaust gas by delaying the timing of ignition when the quantity of the absorbed water reaches a prescribed value determined based on the quantity of saturated water. |
