Control system of engine

A control system of an engine including a cylinder, a piston, and a fuel injector for injecting fuel into the cylinder, the fuel mixing with air to form a mixture gas and combusting inside the cylinder, comprising:

• a water injector for injecting one of supercritical water or subcritical water into the cylinder;
• and
• a controller operatively coupled to the fuel injector and the water injector, wherein within a high engine speed operating range where an engine speed is a given reference speed or above, the controller is configured to control the water injector to inject the one of supercritical water or subcritical water into the cylinder after fuel injection is complete such that an injection timing of the one of supercritical water or subcritical water does not interfere with the fuel injection, the one of supercritical water or subcritical water injected for a given period spanning before a top dead center position of the piston on a compression stroke to after the top dead center position, such that when an injection amount of the one of supercritical water or subcritical water reaches half of a given injection amount, a crank angle of the engine is after the top dead center position, the given injection amount being a total amount of the one of supercritical water or subcritical water injected during the given period;
• and
• wherein within a low engine speed operating range where the engine speed is below the given reference speed, the controller is configured to control the water injector to inject the one of supercritical water or subcritical water for a given period that at least partially overlaps with a period in which a cool-flame reaction of the mixture gas occurs inside the cylinder.