EXHAUST GAS PURIFICATION DEVICE FOR INTERNAL COMBUSTION ENGINE

摘要

In an internal combustion engine, a hydrocarbon intake valve (15) and an exhaust gas purification catalyst (13) are placed in an engine exhaust gas passage. The exhaust gas purification catalyst (13) comprises an upstream-side catalyst (14a) and a downstream-side catalyst (14b) which are arranged in series, wherein the upstream-side catalyst (14a) has a smaller cross-sectional area than that of the downstream-side catalyst (14b). The concentration of a hydrocarbon that flows into the upstream-side catalyst (14a) is oscillated with an amplitude that is 200 ppm or more and falls within a predetermined range and with a period that is 5 seconds or shorter and falls within a predetermined range, whereby NOx contained in an exhaust gas can be reduced on the exhaust gas purification catalyst (13).