Patent ID: 8505280

Claim:
A process for controlling the injection of urea for treatment of nitrogen oxides in a selective catalytic reduction system (SCR) intended to be installed in an exhaust line of an engine of an automotive vehicle, the treatment comprises chemically reducing in an SCR catalyst, nitrogen oxides by adding ammonia contained in urea; the process comprising the following steps: (a) first measuring of the temperature of the gases in the exhaust line of the engine, upstream of the SCR catalyst, then, after measuring the temperature of the gases: (b) injecting urea into the exhaust line if the measured temperature is greater than a predetermined minimum injection temperature, (c) performing steps (c)(i)-(c)(v) if the measured temperature is lower than the minimum injection temperature: (i) determining the quantity of ammonia (Qs) stored in the SCR catalyst, (ii) determining a nitrogen oxide conversion efficiency; (iii) determining the quantity of ammonia (Qn) necessary for obtaining a conversion of nitrogen oxides greater than said conversion efficiency, (iv) comparing the quantity of ammonia (Qs) stored in the SCR catalyst with the quantity of ammonia (Qn) determined in step (c)(iii) necessary for obtaining the conversion of nitrogen oxides greater than said conversion efficiency; and (v) activating a heating mode of the exhaust gases and injecting urea into the system if the quantity of ammonia (Qs) stored in the catalyst is less than the quantity of ammonia (Qn) necessary to obtain the conversion of nitrogen oxides greater than said conversion efficiency.