The provided sketch depicts a cross-section through a four-stroke diesel engine piston, labeled with the following main components:
- Piston Crown: The top, flat surface of the piston that directly receives the force from the burning fuel mixture in the cylinder.
- Piston Rings: These are typically three rings that fit into grooves around the outer circumference of the piston. They slide within the cylinder wall and perform several crucial functions:
- Top Ring (Compression Ring): Seals the combustion chamber by preventing high-pressure gases from leaking past the piston into the crankcase.
- Second Ring (Compression Ring): Provides additional sealing and helps maintain compression in the cylinder.
- Scraper Ring (Oil Control Ring): Scrapes excess oil from the cylinder wall as the piston moves, returning it to the crankcase and preventing excessive oil consumption.
- Piston Skirt: The lower portion of the piston that slides within the cylinder bore. It helps maintain proper piston alignment and minimize friction between the piston and cylinder wall.
- Piston Pin Boss: A reinforced area on the piston where the piston pin is fitted. This area is designed to handle the forces transmitted from the connecting rod.
- Piston Pin: A hollow steel pin that connects the piston to the connecting rod. It allows the piston to pivot slightly within the cylinder while maintaining its connection to the connecting rod.
Gas Force Transfer to Crankshaft (b):
The force generated by the burning fuel mixture in the cylinder is transferred to the crankshaft through a series of connected components:
- Piston Crown: The combustion pressure acts on the piston crown, pushing it downwards with significant force.
- Piston Pin: This force is then transmitted through the piston pin, which connects the piston to the small end of the connecting rod.
- Connecting Rod: The connecting rod acts as a lever arm. As the piston pushes down on the piston pin, the angle between the connecting rod and the crankshaft changes. This causes the crankshaft to rotate on its axis. The big end of the connecting rod is connected to a bearing that sits on the crankshaft journal (a smooth, round surface).
- Crankshaft: The combined force and leverage from the connecting rod create a turning moment on the crankshaft journals. This turning moment causes the crankshaft to rotate, converting the reciprocating (up-and-down) motion of the piston into rotary motion used by the engine to deliver power.
In simpler terms, the combustion force acts like a push on one end of a lever (connecting rod), causing the other end (crankshaft) to rotate. The design of the piston crown, connecting rod, and crankshaft plays a crucial role in efficiently transferring this force and generating usable power for the engine.