Introduction
An interactive 3D model of a cylinder head.
An internal combustion (IC) engine's cylinder head performs several functions.
1. The combustion space can be considered to have three walls; these are the bottom (piston), top (cylinder head) and sides (cylinder liner). The cylinder head provides the top seal for the cylinder bore or sleeve.
2. The cylinder heads provide the structure for holding the exhaust gas valves, intake valves (if fitted) and fuel injectors.
For large diesel engines, each cylinder has its own head casting, which is bolted to the cylinder block. For smaller diesel engines, the engine's head is cast as one piece (multi-cylinder head).
Diesel engines have two methods of admitting and exhausting gasses from the cylinder. They can use either ports, valves, or a combination of both.
Two Stroke Engine Using Ports and Valves
Ports are slots cut into the cylinder walls located in the lower 1/3 of the bore. When the piston travels below the level of the ports, the ports are uncovered/opened, and fresh air or exhaust gasses are able to enter or leave, depending on the type of port. The ports are then covered/closed when the piston travels back above the level of the ports.
Examples of Different Port and Valve Arrangement
Additional Resources
https://en.wikipedia.org/wiki/Cylinder_head
https://www.autobutler.co.uk/wiki/cylinder-head-functions-repairs