Engine system

An engine system comprising:

• a piston that is internally inserted in a cylinder of an engine and moves back and forth in the cylinder;
• a fuel injection valve that is disposed on a top surface of a combustion chamber formed by the cylinder and the piston, and injects a fuel spray along an injection axis;
• a turbocharger that is mounted on the engine and boosts intake air by exhaust energy of the engine;
• a plurality of sensors that output measurement signals in accordance with various parameters relating to operation of the engine;
• a controller that receives the measurement signals of the plurality of sensors, and outputs a control signal to the fuel injection valve in accordance with an operational state defined by a speed and a load of the engine determined from the measurement signals;
• and
• a fuel pressure regulator that increases an injection pressure of the fuel when a total injection amount of the fuel injected to the combustion chamber during one combustion cycle increases, wherein
• the piston comprises:
• a lower cavity provided in a central portion of a top surface of the piston in a radial direction;
• an upper cavity that is provided around the lower cavity and is shallower than the lower cavity;
• and
• a lip portion between the lower cavity and the upper cavity,
• the controller causes the fuel injection valve to execute a main injection performed near a compression top dead center, and at least one pilot injection performed during a compression stroke when the engine operates in a first state and a second state in which the speed is higher than the speed in the first state and a boost pressure of the turbocharger is higher than a boost pressure in the first state,
• the main injection and the at least one pilot injection distribute the fuel spray to the lower cavity and the upper cavity by directing the injection axis to the lip portion in at least one part of an injection period, and
• the controller maintains an injection amount of the main injection and increases an injection amount of the at least one pilot injection when the engine operates in the second state as compared to when the engine operates in the first state, so as to overcome the boost pressure in the second state.