A method and a control system for controlling an internal combustion engine

Method to heat exhaust gases to a selected specific temperature by fuel injection control in an internal combustion engine operated in a four stroke cycle, which ICE comprises a control unit registering the currently requested load and determining a required fuel amount in response to the requested load,

• performing the steps of:
• registering low load operation of the internal combustion engine;
• registering an input from at least one exhaust after-treatment system sensor indicating a detected condition;
• determining an exhaust temperature requirement for the detected condition and calculating a target exhaust temperature;
• selecting a group of cylinders to be regulated for achieving the target exhaust temperature;
• calculating a ratio for desired 1st and 2nd fuel amounts to be injected alternately in consecutive induction strokes for the selected group of cylinders to achieve the target exhaust temperature;
• wherein the ratio defines an offset between an increased 1st fuel amount to be injected in a cylinder of the selected group of cylinders for every second induction stroke, and a reduced 2nd fuel amount to be injected for the intermediate induction strokes,
• characterized by monitoring the exhaust temperature and adjusting the number of selected cylinders to be regulated for achieving the target exhaust temperature.