Spark ignition internal combustion engine

A positive ignition internal combustion engine comprising:

• a cylinder, wherein, a piston reciprocating and coupled with the cylinder, and a cylinder head to operationally define a combustion chamber between the cylinder and the cylinder head;
• a spark plug;
• a pre-chamber made at least partially inside the combustion chamber, wherein, the pre-chamber is confined by a longitudinal and tubular shaped female element, projects into the combustion chamber and comprises a first end stably connected to the cylinder head and a second end opposite to the first end;
• and
• a male element of longitudinal shape, wherein the male element is complementary and coaxial with the longitudinal and tubular shaped female element, and the male element is arranged to make a seal with the longitudinal and tubular shaped female element to pre-compress a mixture, wherein the male element comprises a first end and a second end, wherein the first end is stably connected to an upper surface of the piston to penetrate the longitudinal and tubular shaped female element and the second end is at least in a portion of a relative motion of the piston in the cylinder;
• wherein the spark plug is arranged to project in the pre-chamber;
• the longitudinal and tubular shaped female element includes through openings arranged in a perimeter to remain crossable in any relative position of the male element with respect to the longitudinal and tubular shaped female element;
• and
• when the piston is moving towards a top dead center, a pressure in the pre-chamber is greater than a pressure in the remaining combustion chamber.