Exhaust gas purifying apparatus and exhaust gas purifying method of an engine

摘要

In an SCR apparatus mounted on a vehicle, the concentration of a reducing agent or a precursor thereof contained in an aqueous solution of the reducing agent or the precursor is accurately detected. In sensing the concentration, whether or not the urea water stored in a storage tank is in a stationary state is determined. Only it is in a stationary state, the concentration is detected. The determination of whether or not it is in a stationary state or not is preferably determined by determining whether the vehicle is stopped (S 207 ) and that the period of time TIM that has elapsed after the stoppage has reached a predetermined stationary time TIM1 (S 211 ). The deceleration DCL of the vehicle before stoppage thereof is detected, and the stationary time TIM1 is altered in accordance with the deceleration DCL (S 206 ).