Pistons are an important part of internal combustion engines. Hence, the latter are often referred to as ‘piston engines.’ Besides converting the energy released during combustion into mechanical energy, this key component performs other functions as well. 

In this piece, we’ll cover everything from how pistons are made, parts of a piston, functions, and types.

A piston is a crucial component in a reciprocating engine made up of a solid cylinder of metal. It moves up and down within the cylinder in response to the combustion process in an engine. The motion leads to transforming the energy of combustion into mechanical energy. 

The movement of the piston is driven either by the combustion of the fuel-air mixture inside the cylinder or by the compression of the fuel-air mixture.

In modern engines, pistons are primarily made of aluminium alloys owing to their lightweight nature and efficiency. While most pistons are cast, some might be forged to enhance strength and fatigue life. 

Piston rings, on the other hand, are predominantly made of cast iron or steel alloys. The ring package comprises a wiper ring, a compression ring, and an oil ring. 

Let’s dig deeper into the major parts of a piston and its functions.

1. Piston Rings

Typically made of cast iron and alloy cast iron, piston rings play an important role in engine operation. They serve the most important function of minimising friction between the piston and cylinder walls and preventing gas from leaking in the combustion process. 

There are two main types of piston rings - Compressor rings, which seal the compression chamber, and oil control ring which helps regulate oil consumption.

2. Piston Head/Crown

Located just above the piston, it is the part that comes in contact with the combustion gases, making it experience high temperature and pressure.

3. Piston Skirt

The piston skirt refers to the cylindrical portion of the piston that travels within the cylinder. They are intentionally roughened during manufacturing to retain lubrication and withstand thrust.

4. Piston Pin

Also referred to as a gudgeon pin, this pin connects the piston to the connecting rod. They are made up of harder steel in order to offer good tensile strength.

5. Connecting Rod

The role of connecting rod is to connect the piston to the crankshaft. This allows piston movement within the cylinder and subsequently transmits motion to the engine. The connecting rod is made using cast aluminium alloy and is designed in a manner to withstand piston movement.

6. Connecting Rod Bolt

The primary role of the bolt is to secure the connecting rod to the crankshaft.

7. Piston Bearings

Piston bearings or wrist pin bearings provide support and reduce friction between the piston pin and connecting rod, thus enhancing engine performance and longevity.

Here is a step-by-step explanation of how a piston works:

• Step 1: As the engine runs, the piston moves up and down in the cylinder. At the turning point, it experiences changes in speed. 
• Step 2: The change in speed - first slowing down and then accelerating again leads to inertia forces acting on the piston. These forces, when combined with the gas pressure, create the piston force. 
• Step 3: As a next step, piston force is transferred to the connecting rod and crankshaft, which converts it into rotational motion.
• Step 4: The force coming from expanding combustion gases pushes the piston, leading to the rotation of the crankshaft. Ultimately, the motion is transmitted through a system of gears, effectively transferring the power generated by the piston. 

While there are many different types of pistons, when it comes to piston shapes, these are the notable ones:

1. Flat-top Pistons: As the name suggests, a flat-top piston boasts a flat-top surface. They have the smallest amount of surface space, enabling them to provide efficient combustion. 
2. Dish Pistons: The shape of dish pistons resembles a plate with slightly curled-up outer edges. It is commonly used in boosted applications that do not require high compression ratios.
3. Dome Pistons: Dome pistons feature a raised centre for increased surface area and reduced compression, allowing for efficient energy performance.

The primary role of the piston is to transfer energy by receiving the force generated by the combustion gases within the cylinder. The energy is thereafter transmitted from the connecting rod to the crankshaft. 

Additionally, the piston plays an important part in dissipating the heat generated during combustion by transferring it to the cylinder walls. 

Overall, the functions of a piston include:

1. Energy transfer
2. Heat dissipation
3. Supporting piston rings
4. Guiding the connecting rod 

A good piston must possess the following properties:

1. Strength and Durability: It should have the capability to withstand high temperatures and pressures without cracking during the power stroke. 
2. Lightweight: A lightweight piston helps improve engine efficiency and reduces inertia forces.
3. Low Heat Expansion: The piston design should ensure the minimum effect of thermal expansion during operation. 
4. Balanced Design: A good piston is one which ensures a proper balance between weight, strength, and performance, keeping into account factors such as crown shape, piston skirt design, and more. 

Thus, the piston is a key component of internal combustion engines. From withstanding high temperatures and pressures, it plays a crucial role in ensuring optimal engine performance and efficiency!