CPC F01N 3/208 (2013.01) [F01N 3/035 (2013.01); F01N 3/2066 (2013.01); F01N 13/009 (2014.06); F01N 13/0093 (2014.06); F01N 2250/02 (2013.01); F01N 2560/026 (2013.01); F01N 2570/14 (2013.01); F01N 2590/08 (2013.01); F01N 2610/02 (2013.01); F01N 2610/146 (2013.01); F01N 2900/14 (2013.01); F01N 2900/1402 (2013.01); F01N 2900/1812 (2013.01)] | 14 Claims |
1. A method for controlling urea injection in an exhaust aftertreatment system comprising at least a first catalytic reduction device arranged downstream of a first urea injector, and a second catalytic reduction device arranged downstream of a second urea injector, the method comprising:
injecting urea at a flow rate upstream of the first catalytic reduction device;
measuring a level of nitrogen oxides downstream of the first catalytic reduction device and upstream of the second catalytic reduction device;
controlling the flow rate of the urea injection until the measured level of nitrogen oxides fulfils a predetermined condition;
reducing the flow rate of the urea injection;
when the measured level of nitrogen oxides is decreasing in response to reducing the flow rate of the urea injection, reducing the flow rate of the urea injection further, and
controlling a flow rate of urea injection using the second urea injector upstream of the second catalytic reduction device according to the measured level of nitrogen oxides downstream of the first catalytic reduction device and upstream of the second catalytic reduction device.
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