Engine controlling method and engine system

An engine system including an engine, comprising:

• a controller that stores information regarding a property of a standard fuel;
• an injector that injects fuel into a cylinder of the engine, in response to a control signal from the controller;
• an in-cylinder pressure sensor that is attached to the engine, and outputs to the controller a pressure signal corresponding to a pressure inside the cylinder;
• and
• a crank angle sensor that is attached to the engine, and outputs to the controller a crank angle signal corresponding to a crank angle of the engine,
• wherein during motoring of the engine, the controller causes the injector to inject fuel for analysis at a specific timing after an intake valve of the cylinder is closed,
• wherein the controller acquires a pressure value inside the cylinder at a timing when a specific crank angle period has passed from the fuel injection timing, based on the crank angle signal of the crank angle sensor and the pressure signal of the in-cylinder pressure sensor,
• wherein the information stored in the controller includes a reference pressure value inside the cylinder at a timing when the specific crank angle period has passed after the standard fuel is injected into the cylinder at the specific timing,
• wherein the controller determines the property of the fuel injected by the injector, based on a comparison of the acquired pressure value with the reference pressure value,
• wherein the cylinder is one of a plurality of cylinders,
• wherein the cylinder into which the injector injects the fuel for analysis is the cylinder, out of the plurality of cylinders, whose intake valve is closed first after a crankshaft of the engine starts rotation,
• wherein, for each of the plurality of cylinders, the injector injects the fuel for analysis as a cycle of the engine progresses,
• wherein a corresponding plurality of in-cylinder pressure sensors for the plurality of cylinders output the pressure values of the plurality of cylinders,
• wherein the controller compares an average value of the plurality of pressure values with the reference pressure value to determine the property, and
• wherein the specific crank angle period is set to be shorter as the cycle progresses such that the pressure value is measured without an effect of temperature increase inside the cylinder.