In-cylinder fuel-injection type internal combustion engine, piston for in-cylinder fuel-injection type internal combustion engine and process for manufacturing piston for in-cylinder fuel-injection type internal combustion engine

A process for manufacturing piston for in-cylinder fuel-injection type internal combustion engine,

• the piston comprising:
• a piston body having a top, and being disposed reciprocably within a cylinder in a cylinder block of the internal combustion engine;
• a low thermal conductor for forming a low thermally-conductive zone whose thermal conductivity is lower than that of the surroundings, and the low thermal conductor making at least a part of a fuel collision zone with which liquid fuel is collidable, the liquid fuel being injected from a fuel injection valve into the cylinder, the fuel injection valve being disposed in a cylinder head that is disposed on the cylinder block;
• and a piston head in which the low thermal conductor being disposed on the top of the piston body is cast buried;
• the manufacturing process comprising the steps of:
• adhering a coating material comprising alumina fine particles onto at least a part of one of opposite surfaces of a low thermally-conductive substrate, thereby forming a coating layer on one of the opposite surfaces;
• and
• casting the piston head while contacting the one of the opposite surfaces of the low thermally-conductive substrate that is provided with the coating layer with a molten metal of aluminum alloy, thereby making an aluminum-alloy piston head in which the low thermal conductor is cast buried.