EXHAUST PURIFICATION APPARATUS FOR COMPRESSION IGNITION TYPE INTERNAL COMBUSTION ENGINE

摘要

An internal combustion engine in which an SO x trap catalyst (11) able to trap SO x contained in exhaust gas is arranged in an engine exhaust passage upstream of an NO x storing catalyst (12). The SO x trap catalyst (11) is strengthened in basicity compared with the NO x storing catalyst (12) to an extent so that when the temperature of the SO x trap catalyst (11) is in the temperature range at the time of ordinary operation, that is, substantially 150°C to substantially 400°C, the NO x purification rate by the SO x trap catalyst (11) becomes less than substantially 10 percent of the NO x purification rate by the NO x storing catalyst (12). When NO x should be released from the NO x storing catalyst (12), the air-fuel ratio of the exhaust gas flowing into the SO x trap catalyst (11) is temporarily switched from lean to rich.