METHOD AND DEVICE FOR PURIFYING EXHAUST GAS OF ENGINE

摘要

An engine (1) has first and second cylinder groups (1a) and (1b). The first cylinder group (1a) is connected to a three way (TW) catalyst (8a). The second group (1b) and the TW catalyst (8a) are connected, via an interconnecting duct (13) to an NH3 adsorbing and oxidizing (NH3-AO) catalyst (14a). The first group (1a) performs the rich operation, and the second group (1b) performs the lean operation. In the TW catalyst (8a), NO x exhausted from the first group (1a) is converted to NH3, and the NH3 reduces the NO x exhausted from the second group (1b) in the NH3-AO catalyst (14a). A NO x occluding and reducing (NO x-OR) catalyst (11a) is arranged in the exhaust passage between the second group (1b) and the interconnecting duct (13), to thereby suppress the NO x amount flowing into the NH3-AO catalyst (14a).