SYSTEM FOR TREATING NITROGEN OXIDES WHILE LIMITING AMMONIA EMISSIONS

摘要

The invention relates to a system for treating nitrogen oxides by selective catalytic reduction (SCR), intended to be installed in the engine exhaust system (10) of a vehicle. According to the invention, the nitrogen oxides are chemically reduced in an SCR catalytic converter (12) while injecting ammonia in the form of liquid urea (14), pure or in solution, said liquid urea (14) being stored in a special tank (16) intended to be installed in the vehicle. The system includes a return pipe (11) connecting an outlet of the tank (16) to the exhaust system (10) of the engine such as to direct the ammonia vapour emitted during the breakdown of the urea in the tank (16) towards the engine exhaust system (10) upstream of the SCR catalytic converter (12).