EXHAUST EMISSION CONTROL SYSTEM OF INTERNAL COMBUSTION ENGINE AND EXHAUST EMISSION CONTROL METHOD

摘要

In an exhaust emission control system of an internal combustion engine, a NOx selective reduction catalyst (15) is disposed in an engine exhaust passage, and an aqueous solution of urea stored in an aqueous-urea tank (20) is supplied to the NOx selective reduction catalyst (15) so as to selectively reduce NOx. A NOx sensor (41) is provided in the engine exhaust passage downstream of the NOx selective reduction catalyst (15) for detecting the NOx conversion efficiency of the NOx selective reduction catalyst (15), and the concentration of aqueous urea in the aqueous-urea tank (20) is estimated from the detected NOx conversion efficiency. The exhaust emission control system and method make it possible to detect the concentration of aqueous urea at reduced cost.