Most people should be familiar with pistons. Pistons can not only achieve high-frequency reciprocating motion but also provide good sealing. According to some sources currently available, pistons likely originated in Egypt or China, with ancient Chinese bellows used for smelting being a typical example. The advent of the steam engine during the First Industrial Revolution promoted the rapid development of piston-type devices. With the development of the steel industry and the gradual application of petroleum fuels, the internal combustion engine emerged, in which the piston is the most critical component, even considered the heart of the internal combustion engine. According to relevant information, the earliest internal combustion engine pistons were made of cast iron. In the early 20th century, pistons began to be made from aluminium alloys. In recent decades, with engines evolving towards smaller size, higher speed, greater power and higher compression ratios, the internal temperature and pressure of engines have further increased, making aluminium-based composite materials gradually become the more ideal material for manufacturing engine pistons.

The engine piston mainly consists of three parts: the piston crown, the piston head, and the piston skirt. The piston crown and the cylinder wall form the engine's combustion chamber, where the fuel-air mixture burns to push the piston downwards. The piston crown must endure high temperatures and pressures, with temperatures generally reaching 300-400°C and gas pressures up to 3-5 MPa for petrol engines and 6-9 MPa for diesel engines. The piston head is the part from below the piston crown to the oil ring groove, with three main functions: transmitting temperature and pressure, sealing the cylinder, and transferring heat to the cylinder wall. The piston head is fitted with compression rings and oil rings, which are metal rings embedded in the piston grooves. The compression rings seal the combustible mixture in the combustion chamber, while the oil rings, in addition to sealing, remove excess oil from the cylinder. Oil return holes are also machined at the bottom of the oil ring groove to allow the scraped oil to flow back to the oil sump. The piston skirt extends from the bottom of the oil ring groove to the piston underside, primarily to withstand pressure and provide guidance and control for the piston's movement. The piston skirt is equipped with a piston pin and connecting rod assembly linked to the crankshaft.

The lubrication of the piston mainly concerns the lubrication required between the piston and the cylinder wall as well as at the piston pin. Taking a petrol engine as an example, the lubrication between the piston and the cylinder wall uses a splash lubrication method. The advantage of this method is that the lubricant is splashed upwards and around through the movement of the connecting rod and crankshaft, and then, through the reciprocating movement of the piston and the scraping action of the oil ring, the lubricant can cover the cylinder wall fairly evenly without entering the combustion chamber in large quantities. Of course, this lubrication method can easily lead to wear of the piston rings and cylinder wall if the oil at the bottom is insufficient. Another part of the piston that requires effective lubrication is the piston pin, which also mainly uses splash lubrication. If there is insufficient oil at the bottom or if the oil viscosity is too high, it is very likely to cause inadequate lubrication, and under high temperature and pressure, deformation and damage may occur. Although engine pistons are equipped with a compression ring and an oil ring to achieve good sealing, it still cannot completely prevent blow-by or a very small amount of lubricant from entering the combustion chamber. Under normal circumstances, this will not affect the engine, but if it exceeds a certain amount, it can adversely affect the engine, such as accelerated wear of the piston and cylinder wall, increased oil consumption and aging, reduced engine power, and higher fuel consumption. Therefore, for effective piston lubrication, the most important aspect is to ensure an adequate amount of lubricant and to replace it in a timely manner with quality oil.

Due to the author's limited ability and knowledge, there are inevitably mistakes, and thanks to point them out.