The whole piston can be divided into 3 parts, piston top, piston head and piston skirt. The main function of the piston is to withstand the combustion pressure in the cylinder and pass this force through the piston pin and connecting rod to the crankshaft.
In addition, the piston also with the cylinder cover, cylinder wall together to form a combustion chamber. Piston Top is a part of the combustion chamber, so often made into different shapes, gasoline engine piston at most the use of flat top or concave roof, in order to make the combustion chamber structure compact, small heat dissipation area, manufacturing process is simple. The convex top piston is commonly used in two-stroke gasoline engine.
The piston top of the diesel engine is often made into various pits. The piston head is the part of the piston pin above, the piston head is fitted with a piston ring to prevent high temperature, high pressure gas from channeling into the crankcase, while preventing the oil from entering the combustion chamber, and most of the heat absorbed by the top of the piston is also passed through the piston head to the cylinder, which is then passed through the cooling medium.