METHOD AND DEVICE FOR INTRODUCING A FLUID INTO AN EXHAUST-GAS PURIFICAT ION SYSTEM

摘要

Method and device for introducing liquid into an exhaust-gas purification system The nitrogen oxides emitted by an internal-combustion engine operated with excess of air are normally converted by the method of selective catalytic reduction (SCR) by bringing the nitrogen oxides, together with ammonia, into contact with a selective catalyst. In a motor vehicle, because of the dangers associated with the use of ammonia, ammonia should be carried only in the form of a substance which liberates ammonia, generally an aqueous urea solution. The problem solved by the invention consists in avoiding frost damage to sections of the exhaust-gas purification system during shutdown times and in making possible the operation of such a system at temperatures below the freezing point of the reducing agent solution used. For this purpose, the invention makes provision for the device (2) to comprise a (thermally insulated) reservoir (6) for the reducing agent liquid (4) and a liquid supply line (12) which is connected thereto and which terminates in an outlet opening (22) for the liquid (4). The reservoir (6) and the liquid supply line (12) can be heated. Furthermore, a heater (38) is provided for liquefying a starting volume (14) which is small compared with the volume of the reservoir (6). The liquid supply line (12) may also have a back-flush valve (20) to which a gas (30) which is under pressure can be applied. Said supply line (12) can consequently be blown free.