| 摘要 |
Disclosed is an exhaust gas purification method, and also disclosed is an exhaust gas purification system (1). The exhaust gas purification system (1) comprises, in order from the upstream side of an exhaust passage (11) of an internal combustion engine (10), a NOx occlusion-reduction catalyst (32) for purifying NOx contained in exhaust gas, an HC-adsorbing member (33) for adsorbing hydrocarbons contained in exhaust gas, and a catalyzed DPF (34) or oxidation catalyst for purifying PM contained in exhaust gas. During the implementation of NOx regeneration control for restoring the NOx occlusion capacity of the NOx occlusion-reduction catalyst (32) in this system, the air-fuel ratio of the exhaust gas in terms of excess air factor is taken to be 0.8 to 1.1 when an index temperature (Tc) serving as an index of the temperature of the HC-adsorbing member (33) is a first judgment temperature or less, is taken to be 1.0 to 1.1 when the index temperature (Tc) is between a first judgment temperature and a second judgment temperature, and is taken to be 0.8 to 1.1 when the index temperature (Tc) is a second judgment temperature or above. As a result, during the exhaust gas air-fuel ratio rich control for restoring the NOx occlusion capacity which is implemented during the purification of the NOx and PM contained in the exhaust gas by the NOx occlusion-reduction catalyst and the catalyst-supported DPF (34), the outflow of HC to the atmosphere is improved. |
