FIELD: chemistry.
SUBSTANCE: method of determining the quality of an ammonia-containing reducing agent, used to reduce the content of nitrogen oxides in a SCR system (21) for treatment of exhaust gases, the method including controlling operation of a dosing unit (14) for releasing a predetermined dosed amount of the solution of a reducing agent into the exhaust gases of an internal combustion engine. A nitrogen oxide sensor (17) with cross sensitivity to ammonia, placed downstream a SCR catalyst (20) for selective neutralisation of the SCR system (21) for treatment of exhaust gases, is used to determine and compare with predetermined limiting values a value of efficiency at least correlated with the efficiency (ε) of the SCR catalyst (20) for selective neutralisation. A first given dosed amount (D) and a first limiting value are provided at the first step of the method in normal dosing mode. If, through comparison, a value of efficiency is established, which does not correspond to the proper operation of the SCR system (21) for treatment of exhaust gases, the normal dosing mode is terminated and replaced, at the second step of the method, with a diagnostic mode, wherein for a first time interval a second given dosed amount (D) which is greater than the first and a second limiting value are provided. If the value of efficiency established at the end of the first time interval deviates from the second limiting value, at the third step of the method conditioning of the catalyst (20) for selective neutralisation is carried out such that the amount of ammonia accumulated in the SCR catalyst (20) for selective neutralisation is less than the given limiting value of the accumulated amount. In adaptation mode, a third dosed amount (D) and a third limiting value are provided as the fourth step of the method for the given second time interval. Improper quality of the solution of the reducing agent is diagnosed if deviation of the value of efficiency from the third limiting value is established at the end of the second time interval.
EFFECT: accurate detection of low quality of a solution of a reducing agent, which prevents hazardous emissions.
20 cl, 3 dwg
