INTERNAL COMBUSTION ENGINE EXHAUST GAS PURIFICATION DEVICE

摘要

In an internal combustion engine, a hydrocarbon supply valve (16), an exhaust gas purification catalyst (13), a urea water supply valve (17) and a NOx selective reduction catalyst (15) are arranged in that order in an engine exhaust gas passage. The disclosed device selectively uses a first NOx purification method, in which the NOx contained in the exhaust gas is reduced in an exhaust gas purification catalyst (13) by oscillating, at an amplitude and period in a pre-determined range, the concentration of carbohydrates flowing into the exhaust gas purification catalyst (13), and a second NOx purification method in which NOx is reduced in a NOx selective reduction catalyst (15) by means of supplied urea water.