A piston is a crucial component found in various mechanical systems. Let me explain its role and function:

1. Definition:

   • A piston is a disc-shaped component that reciprocates (moves up and down) inside a cylinder.
   • It is commonly used in reciprocating engines, pumps, compressors, and hydraulic cylinders.
   • The primary purpose of a piston is to transfer force between different parts of the system.

2. Internal Combustion Engines:

   • In an internal combustion engine, the piston is acted upon by the pressure of expanding combustion gases in the combustion chamber.
   • This force is transmitted through the connecting rod to the crankshaft, which converts it into rotational motion.
   • The piston is attached to the connecting rod via a swiveling gudgeon pin (also known as a wrist pin).
   • Gas sealing is achieved using piston rings, which are narrow iron rings fitted into grooves in the piston just below the crown.
   • These rings provide gas sealing and help maintain compression.

3. Function Reversal in Pumps:

   • In a pump, the function of the piston is reversed.
   • The force is transferred from the crankshaft to the piston, compressing or ejecting the fluid in the cylinder.
   • Some engines also use the piston as a valve, covering and uncovering ports in the cylinder.

4. Variations and Considerations:

   • Piston design can vary based on factors such as engine type, supercharging level, and working conditions.
   • High-power diesel engines operate under challenging conditions, with maximum pressures in the combustion chamber reaching up to 20 MPa and surface temperatures exceeding 450°C.
   • Proper cooling design, including cooling cavities supplied with oil, helps manage these extreme conditions.