Exhaust aftertreatment system

An exhaust aftertreatment system for an internal combustion engine comprising:

• a reagent storage tank;
• a pump in fluid communication with the reagent storage tank;
• a first reagent dosing device in fluid communication with the pump;
• a first selective catalytic reduction (SCR) device arranged downstream of the first reagent dosing device;
• one or more further reagent dosing devices arranged downstream of the first selective catalytic reduction (SCR) device, said one or more further reagent dosing devices being in fluid communication with said pump;
• and
• one or more further selective catalytic reduction (SCR) devices arranged downstream of a respective one of said one or more reagent dosing devices;
• and
• a controller communicatively coupled to the pump and the first and said one or more further reagent dosing devices wherein said one or more further reagent dosing devices is/are arranged in series with the first reagent dosing device, and wherein the controller comprises a dosing device diagnostic circuit configured to
• in a first stage performing a diagnosis of operational performance of all reagent dosing devices by executing the steps of
• a) measuring pump motor speed while all reagent dosing devices dose at two operating points, computing a first stage diagnostic, and evaluating the first stage diagnostic;
• b) comparing the evaluated first stage diagnostic with a nominal first stage diagnostic;
• c) in case a deviation is determined in step b) the dosing device diagnostic circuit further configured to
• identify a faulty reagent dosing device by executing in a second stage the steps of
• d) disabling all further reagent dosing devices or setting all further reagent dosing devices to dose at a low quantity of less than 10% of a maximum dosing amount while simultaneously activating the first reagent dosing device to dose at the two operating points, and evaluating a second stage diagnostic;
• e) comparing the evaluated second stage diagnostic with a nominal second stage diagnostic for determining if the first dosing device is operating correctly or is faulty;
• and
• in a third stage executing the steps of
• f) disabling the first reagent dosing device or setting the first reagent dosing device to dose at a low quantity of less than 10% of the maximum dosing amount while simultaneously activating only one of said one or more further reagent dosing devices to dose at the two operating points, and evaluating a third stage diagnostic;
• and
• g) comparing the evaluated third stage diagnostic with a nominal second stage diagnostic for determining if said only one of said one or more further reagent dosing devices is operating correctly or is faulty.