Engine system with fuel system control arrangement and method for controlling fuel injection in an internal combustion engine

An engine system including a fuel system control arrangement, comprising:

• an internal combustion engine comprising an exhaust line, one or more cylinders, and one or more fuel injectors corresponding to the one or more cylinders and arranged for injecting fuel into the one or more cylinders;
• means for determining fresh air mass flow into an intake to the engine;
• a nitrogen oxide (NOx) sensor in the exhaust line;
• and
• a controller configured to determine oxygen (O2) in exhaust gas based on a signal from the NOx sensor and to calculate a current fuel injection quantity based on the O2 in the exhaust gas and determined fresh air mass flow into the intake, to compare the current fuel injection quantity into the one or more cylinders to a theoretical fuel injection quantity into the one or more cylinders under current operating conditions, and to respond to a determination that the current fuel injection quantity differs from the theoretical fuel injection quantity by adjusting an amount of fuel injection from the one or more fuel injectors to make the current fuel injection quantity closer to the theoretical fuel injection quantity.