| abstract |
In an internal combustion engine, a first exhaust passage (22a) and a second exhaust passage (22b) branched from an exhaust passage (21) are provided. NOx occlusion reduction catalysts (23a, 23b) and particulate filters (24a, 24b) are disposed respectively in the exhaust passages (22a, 22b). For example, when NOx is released from the NOx occlusion reduction catalyst (23a) within the first exhaust passage (22a), fuel is added through a fuel addition valve (32) in such a state that the exhaust gas is allowed to flow into only the first exhaust passage (22a). When the added fuel is deposited onto the NOx occlusion reduction catalyst (23a), a first exhaust control valve (26a) is temporarily closed to bring the fuel-air ratio of the exhaust gas to a rich state. |