Combustion-chamber structure of engine

A combustion-chamber structure of an engine, comprising:

• a cylinder block;
• a cylinder head;
• a piston;
• a valve;
• and
• a combustion chamber partitioned by the cylinder block, the cylinder head, the piston, and the valve,
• wherein said valve is configured to open or close a port opening to said combustion chamber and comprises an umbrella part and a stem part,
• said umbrella part of the valve includes a valve body which includes a valve head facing the combustion chamber and a valve face positioned on an opposite side to the combustion chamber, a heat-insulation layer which is provided at the valve head and has smaller heat conductivity than said valve body, a heat-barrier layer which is provided to cover said valve head provided with said heat-insulation layer and has smaller heat conductivity than said valve body and said heat-insulation layer, and a heat-diffusion layer which is provided between said heat-insulation layer and said heat-barrier layer and has larger heat conductivity than said heat-insulation layer and said heat-barrier layer, and
• said heat-diffusion layer comprises a contact portion which is provided to extend up a position of said umbrella part of the valve which contacts with said cylinder head when the valve is closed.