Exhaust emission control system for internal combustion engine, and control method for exhaust emission control system

摘要

An exhaust emission control system for an internal combustion engine (1) includes: an urea aqueous solution addition valve (230) that supplies urea aqueous solution to an exhaust passage (26); and an urea aqueous solution supply tube (240) that supplies urea aqueous solution to the urea aqueous solution addition valve (230). When it is determined that a second exhaust gas temperature (TH2) upstream of a selective reduction NOx purification catalyst (41) is higher than or equal to a reference temperature (YES in step S11), a control device (80) executes recovery control for recovering urea aqueous solution in the urea aqueous solution supply tube (240) (step S14).