The high heat generated by the combustion is passed through the piston ring to the cylinder wall, so it can play the role of cooling the piston. The piston ring from the cylinder wall to heat, which can reach the top of the piston under heat 30~40%.
The first function of the piston ring is to keep the seal between the piston and the cylinder wall to control the air leak to the minimum. This role is mainly borne by the gas ring, the engine at any operating conditions, the compressed air and gas leakage shall be kept to a minimum, in order to improve the thermal efficiency; to prevent leakage caused by between cylinder and piston or cylinder and ring; to prevent deterioration of lubricating oil caused by failure.
The second function of the piston ring is to properly scrape the lubricating oil that is attached to the cylinder wall and maintain the normal oil consumption. When the supply of lubricating oil is too much, it will be sucked to the combustion chamber, which makes the fuel consumption increase, and the effect on engine performance is very bad because of the coke produced by the combustion.
Because the piston is slightly smaller than the inner diameter of the cylinder, if there is no piston ring, the piston is unstable in the cylinder, so it is impossible to move freely. At the same time, the ring also prevents the piston from contacting directly with the cylinder and plays a supporting role. Therefore, the piston ring moves up and down in the cylinder, and its sliding surface is borne entirely by the ring.