Engine controlling method and engine system

An engine system, comprising:

• an engine mounted on a vehicle and having an injector, a spark plug, and a property adjusting device;
• an accelerator operation detector configured to detect operation of an accelerator pedal of the vehicle;
• and
• a controller configured to output a control signal to each of the injector, the spark plug, and the property adjusting device, based on a detection signal from the accelerator operation detector,
• wherein the engine selectively performs flame propagation combustion in which fuel injected into a cylinder from the injector is forcibly ignited using the spark plug, and compressed self-ignition combustion in which fuel injected into the cylinder from the injector carries out compressed self-ignition without using the spark plug, and
• wherein the controller is configured to:
• receive the detection signal from the accelerator operation detector, and set a target torque of the engine in a specific cycle in the future by a given delay time from a present time, based on a present accelerator opening;
• preselect combustion in the specific cycle according to the target torque from the flame propagation combustion and the compressed self-ignition combustion;
• output a control signal to the property adjusting device before the specific cycle so that a property inside the cylinder in the specific cycle becomes a property corresponding to the selected combustion;
• estimate the property at a timing when an intake valve is closed in the specific cycle, based on a sensor signal measured in the specific cycle;
• and
• output a control signal corresponding to the estimated property to the spark plug or the injector so that the preselected combustion is realized in the specific cycle.