System for preventing knocking and method for controlling the same

A method for controlling a system for preventing knocking comprising:

• providing a first injector mounted at an upper surface of a cylinder at a predetermined distance from a central axis of a piston and injecting a main fuel including gasoline into a combustion chamber, and a second injector that includes a first slanted surface and is mounted at the upper surface of the cylinder on the central axis of the piston and injecting a sub fuel including ethanol into the combustion chamber;
• detecting state variables of an engine;
• controlling injection of the main fuel according to the state variables of the engine;
• controlling ignition;
• determining whether knocking occurs;
• and
• controlling injection of the sub fuel in a case that the knocking occurs;
• wherein the second injector includes a needle head having an inverted and truncated cone shape;
• wherein an upper side of the inverted and truncated cone shape has a second slanted surface corresponding to the first slanted surface;
• wherein the needle head is selectively movable in the second injector such that the sub fuel is injected in a hollow right circular cone shape through a space formed between the first slanted surface and the second slanted surface by the second injector so as to directly inject the sub fuel into an end-gas zone of the combustion chamber;
• wherein an angle between confronting generating lines of the hollow right circular cone shape is formed for the sub fuel to be injected to the end-gas zone.