Method for modifying combustion chamber in a reciprocating piston internal combustion engine and resulting engine

A method for improving combustion in a main combustion chamber of an internal combustion engine, the engine including a main combustion chamber arranged between a head and a reciprocating piston, the method comprising:

• providing a heat retaining element between the head and the main combustion chamber, the heat retaining element being configured to reduce heat transfer from the main combustion chamber into the engine head;
• and
• providing a precombustion chamber including a reaction chamber, the reaction chamber being configured to be provided with a secondary charge of air/fuel and a first spark igniter, the reaction chamber communicating with the main combustion chamber via a plurality of discharge channels configured to discharge fuel radical species from the reaction chamber into the main combustion chamber, the fuel radical species being generated from the secondary charge,
• wherein the heat retaining element is a self-supporting structure coupled to the head, the heat retaining element including a head-facing portion substantially corresponding in shape to a portion of the head facing the main combustion chamber.