Engine system

A engine system, comprising:

• an engine having a cylinder and a piston reciprocatably accommodated in the cylinder;
• an injector attached to the engine and configured to inject fuel into the cylinder;
• a spark plug attached to the engine and configured to ignite a mixture gas of fuel and intake air, the intake air containing fresh air and burnt gas;
• a variable valve operating device connected to an intake valve and an exhaust valve, and configured to control opening and closing of the intake valve and the exhaust valve to adjust a filling amount of the intake air;
• and
• a controller electrically connected to the injector, the spark plug, and the variable valve operating device, and configured to control the injector, the spark plug, and the variable valve operating device according to a demanded load of the engine,
• wherein when the engine operates at a given speed and the demanded engine load is a first load, the controller controls the injector and the variable valve operating device to make a mass ratio (G/F) of the intake air inside the cylinder to fuel be at a first G/F, and controls the spark plug so that the mixture gas inside the cylinder combusts by flame propagation,
• wherein when the engine operates at the given speed and the demanded engine load is a second load lower than the first load, the controller controls the injector and the variable valve operating device to make the mass ratio be at a second G/F higher than the first G/F, and controls the injector to make an injection center of gravity be at a first timing so that the entire mixture gas inside the cylinder combusts by compression ignition, the injection center of gravity being defined based on an injection timing and an injection amount of fuel during one cycle,
• wherein when the engine operates at the given speed and the demanded engine load is lower than the first load and higher than the second load, the controller controls the injector and the variable valve operating device to make the mass ratio be at a third G/F higher than the first G/F and lower than the second G/F, and controls the injector to make the injection center of gravity be at a second timing later than the first timing so that at least part of the mixture gas inside the cylinder combusts by compression ignition,
• wherein when the engine operates at the given speed and the demanded engine load is lower than the first load and higher than the second load, the controller inhibits the operation of the spark plug so that the entire mixture gas inside the cylinder combusts by compression ignition,
• wherein when the engine operates at the given speed and the demanded engine load is the second load, the controller controls the injector to inject fuel during an intake stroke,
• wherein when the engine operates at the given speed and the demanded engine load is lower than the first load and higher than the second load, the controller controls the injector to inject fuel during each of the intake stroke and a compression stroke, and
• wherein when the engine operates at the given speed and the demanded engine load is lower than the first load and higher than the second load, the controller switches between a first injection mode and a second injection mode based on an estimated G/F, and an estimated temperature inside the cylinder at a close timing of the intake valve, the first injection mode being a mode in which the controller controls the injector to inject fuel during each of the intake stroke and a middle period of the compression stroke, and the second injection mode being a mode in which the controller controls the injector to inject fuel during each of the intake stroke and an end period of the compression stroke.