Piston and Types of Piston, Definition, Function, PDF

Piston Definition:

A piston is cylindrical in shape and forms the movable portion of the combustion chamber.

A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, and pneumatic cylinders among other similar mechanisms.

In an engine, it's purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and connecting rod. or 

The force due to this pressure is transmitted to the connecting rod via the piston.

The below diagram or GIF showed that how the piston works in the cylinder.

The connecting rod helps to change the reciprocating motion of a piston into a revolving motion at the crankshaft.

Pistons are commonly made of a cast aluminum alloy for excellent and lightweight thermal conductivity. (Thermal conductivity is the ability of a material to conduct and transfer heat). 

Piston Function:

Movement of the piston is in the cylinder and transfer force of expanding gas via connecting rod to the crankshaft and from crank to piston in reverse direction.

The compressing gas allows the injection of fluid in the cylinder.

This also acts as controlling the valve.

It serves as a heat transfer medium to the cylinder walls.

It acts as a guide to the small end of the connecting rod.

Piston Characteristic:

The piston should be strong enough to sustain:

Hammering effect of combustion gas pressure,

Fluctuating load and

A high temperature of the gases.

The piston should be:

Light in weight

silent in operation and

Mechanically strong.

Due to the lightweight:

Inertia losses and

The inertia loads reduce on the bearing, due to change in motion.

Piston Application or uses:

The main application of the Piston is:

1. Reduced inertia also improves the mechanical efficiency of the engine.
2. It compresses the fluid inside the cylinder hence increases the pressure and temperature of the fluid inside the cylinder.
3. It also provides the direction.

Piston Advantages:

The main advantages of the Piston are:

1. Mechanical simplicity
2. Flexibility and reliability
3. Power to weight ratio
4. Multi-fuel capability
5. Low turbine operating temperature
6. Less vibration and noise
7. Less maintenance
8. Easy to start the piston
9. Highly suitable for waste heat recovery
10. Give a high degree of maneuverability
11. Less manufacturing cost
12. Low NOx emissions
13. It offers the HCCI combustion process
14. Internally balanced
15. Modularity

Piston Disadvantages:

The main disadvantages of the Piston are:

• Poor fuel economy
• Stability of fuel supply
• Poor part load efficiency
• High combustion rate
• Reduction gearing is require

Types of Piston:

Piston consists of 10 different types which are:

1. Taper Piston
2. Cam ground Piston
3. Special alloys 
4. Wire wound 
5. Autothermic 
6. Bimetal 
7. Cast steel 
8. Tinned 
9. Oil cooled and
10. Two-piece pistons

Taper:

This is sometimes turned taper, the diameter of the crown side is smaller than the skirt end.

As higher temperature occurs towards the crown, that sides expand more than the skirt, due to which it's diameter becomes uniform under running conditions.

Cam ground:

Cam ground, such that they have an elliptical section instead of the circular one.

The minor diameter of the ellipse lies in the direction of the piston-pin axis.

Special alloys:

The special alloy having a low coefficient of expansion.