Abstract This paper conducts research on the fuel accommodation control of a fuel-flexible engine. Blended fuels from gasoline and diesel are tested on a compression ignition engine. Two problems with the fuel-flexible engine are studied. One problem is that the engine brake torque output is different with different fuels, and the other problem is that the thermal efficiency deteriorates without recalibration. One open-loop control method and one closed-loop control method based on cylinder pressure sensor are proposed to deal with the fuel accommodation control problems. The open-loop control method features fuel blend ratio detection, which is a new dimension of input for the conventional MAP based engine management system. Gasoline and diesel blend ratio detection methods are studied, and the result also provides information for the closed loop control method as a feedforward controller. An indicated mean effective pressure based method is proposed for the engine brake torque difference problem, and a feedback controller with indicated mean effective pressure maximum seeking algorithm is used to optimize engine efficiency. The fuel injection amount and timing will be adjusted according to the fuel estimation result and the feedback control algorithms. Results show that the methods proposed could identify fuel blend ratio quite accurately, the engine brake torque output could follow the target value well, and the engine thermal efficiency could be optimized.