APPARATUS FOR PURIFYING EXHAUST GAS IN INTERNAL COMBUSTION ENGINE

摘要

In an internal combustion engine, an NO_x selective reduction catalyst (15) is disposed within an engine exhaust gas passage. Urea is supplied to the NO_x selective reduction catalyst (15), and ammonia produced from the urea is adsorbed onto the NO_x selective reduction catalyst (15). NO_x contained in an exhaust gas is selectively reduced mainly by the adsorbed ammonia. An NO_x sensor (29), which can detect NO_x and ammonia contained in the exhaust gas, is disposed within the engine exhaust gas passage located downstream of the NO_x selective reduction catalyst (15). Whether or notthe amount of ammonia adsorbed on the NO_x selective reduction catalyst (15) is saturated is determined based on the value detected by the NO_x sensor (29) during the stop of the supply of a fuel into the engine in reduced speed operation.