Engine control method and engine system

A control method for an engine which is mounted to a vehicle having steerable road wheels and mechanically coupled to drive road wheels of the vehicle, and which includes a spark plug and a fuel injector, the control method comprising:

• a combustion mode setting step of selecting a combustion mode of the engine between a first combustion mode in which an entirety of an air-fuel mixture in a cylinder of the engine is combusted by a propagation of a flame produced by the spark plug, and a second combustion mode in which at least a part of an air-fuel mixture in the cylinder is combusted by a self-ignition, on the basis of an operating state of the engine;
• a decremental torque setting step of setting a torque reduction amount by which an output torque of the engine is to be reduced, on the basis of a steering angle of the steerable road wheels;
• a first torque reduction step of controlling the spark plug based on the torque reduction amount set in the decremental torque setting step so as to retard an ignition timing, when the first combustion mode is selected in the combustion mode setting step;
• and
• a second torque reduction step of controlling the fuel injector based on the torque reduction amount set in the decremental torque setting step so as to reduce a fuel injection amount, when the second combustion mode is selected in the combustion mode setting step.