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.

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

How does pistons work?

Movement of the piston is inside the cylinder and it transfers the 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 helps in controlling the valve. It serves as a heat transfer medium to the cylinder walls.

Piston Characteristic

The piston should be strong enough to sustain the following:

• Hammering effect of combustion gas pressure
• Fluctuating load
• High temperature of the gases

The piston should be:

• Light in weight
• Silent in operation
• Mechanically strong

Due to the lightweight, there is Inertia losses. The inertia loads reduce on the bearing, due to changes in motion.

Piston Application or uses

The main application of the Piston are as follows:

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

Piston Advantages

The main advantages of the Piston are:

• Mechanical simplicity
• Flexibility and reliability
• Power to weight ratio
• Multi-fuel capability
• Low turbine operating temperature
• Less vibration and noise
• Less maintenance
• Easy to start the piston
• Highly suitable for waste heat recovery
• Give a high degree of maneuverability
• Less manufacturing cost
• Low NO_x emissions
• It offers the HCCI combustion process
• Internally balanced
• 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

Following are the types of Piston:

• Taper Piston
• Cam ground Piston
• Special alloys 
• Wire wound 
• Autothermic 
• Bimetal 
• Cast steel 
• Tinned 
• Oil cooled and
• Two-piece pistons

Taper piston

This is sometimes turned taper, the diameter of the crown side is smaller than the skirt end. As higher temperature occurs towards the crown, the sides expand more than the skirt, due to which its diameter becomes uniform under running conditions. It is designed with a tapered shape, which allows for better heat dissipation and reduces the risk of hot spots, which can cause engine damage. Taper pistons are commonly used in high-performance engines, such as those found in racing cars or aircraft.

Advantages:

• Improved Combustion: Taper pistons allow for better air and fuel mixing. This can result in more efficient combustion and improved performance.
• Reduced Friction: Taper pistons can reduce friction between the piston and cylinder wall. This can lead to improved fuel economy and reduced emissions.

Disadvantages:

• Cost: Taper pistons can be more expensive to manufacture due to their complex design.
• Durability: Taper pistons may be more prone to wear and tear than other piston designs.

Cam ground piston

Cam Ground Piston is designed with a cam-shaped profile on the skirt, which helps to reduce friction and improve engine efficiency. Cam ground pistons are commonly used in diesel engines, where efficiency is critical.

Advantages:

• Reduced Friction: Cam ground pistons can reduce friction between the piston and cylinder wall. This can result in improved fuel economy and reduced emissions.
• Improved Combustion: Cam ground pistons can improve air and fuel mixing which can result in more efficient combustion.

Disadvantages:

• Cost: Cam ground pistons can be more expensive to manufacture due to their complex design.
• Limited Applicability: Cam ground pistons may not be suitable for all engine types.

Special alloys piston

Special alloys are also used to manufacture pistons, such as aluminum or titanium alloys. These alloys offer several benefits, such as better heat dissipation, increased strength, and reduced weight. Special alloy pistons are commonly used in high-performance engines, where weight reduction is critical.

Advantages:

• Improved Durability: Special alloys can offer improved resistance to wear and tear.
• Improved Performance: Special alloys can offer improved heat resistance and strength.

Disadvantages:

• Cost: Special alloys can be more expensive than other materials used in piston manufacturing.
• Availability: Some special alloys may be more difficult to source than other materials.

Wire wound pistons

Wire wound pistons are also available in the market. They are designed with a wire mesh that is wrapped around the piston skirt, which helps to reduce friction and improve engine efficiency. Wire wound pistons are commonly used in diesel engines, where efficiency is critical.

Advantages:

• Improved Heat Resistance: Wire wound pistons can offer improved heat resistance and thermal stability.
• Reduced Weight: Wire wound pistons can be lighter than other piston designs. This can result in improved fuel economy and performance.

Autothermic pistons

Autothermic pistons are designed with a special coating that helps to reduce friction and improve engine efficiency. This type of piston is commonly used in high-performance engines, where efficiency is critical.

Advantages:

• Improved Combustion: Autothermic pistons can improve combustion efficiency and reduce emissions.
• Reduced Weight: Autothermic pistons can be lighter than other piston designs.

Disadvantages:

• Cost: Autothermic pistons can be more expensive to manufacture due to their complex design and specialized materials.
• Limited Applicability: Autothermic pistons may not be suitable for all engine types, and may require specific modifications to the engine to be compatible.

Bimetal pistons

Bimetal pistons are designed to withstand high temperatures and pressures, making them ideal for high-performance engines. These pistons are made up of two different metals, typically aluminum and steel. The aluminum outer layer provides excellent thermal conductivity, while the steel inner layer provides strength and durability. Bimetal pistons are known for their excellent resistance to wear and tear, making them a popular choice for racing and heavy-duty applications.

Advantages:

1. Improved Durability: Bimetal pistons can offer improved resistance to wear and tear.
2. Reduced Friction: Bimetal pistons can reduce friction between the piston and cylinder wall. This can lead to improved fuel economy and reduced emissions.

Disadvantages:

• Cost: Bimetal pistons can be more expensive to manufacture due to their complex design and specialized materials.
• Limited Applicability: Bimetal pistons may not be suitable for all engine types. They may require specific modifications to the engine to be compatible.

Cast steel pistons

Cast steel pistons are another popular type of piston used in diesel engines, industrial machinery, and marine engines. These pistons are made from a cast steel alloy, which provides high strength and durability. Cast steel pistons have a longer lifespan and can withstand high pressures and temperatures, making them ideal for heavy-duty applications. They are also known for their resistance to thermal expansion, which helps prevent piston scuffing and seizing.

Advantages:

• Improved Durability: Cast steel pistons can offer improved resistance to wear and tear, which can result in increased engine longevity.
• Improved Heat Resistance: Cast steel can offer improved heat resistance and thermal stability.

Disadvantages:

• Cost: Cast steel pistons can be more expensive to manufacture.
• Limited Applicability: Cast steel pistons may not be suitable for all engine types.

Tinned pistons

Tinned pistons are primarily used in small engines, such as those found in lawn mowers, chainsaws, and other outdoor equipment. These pistons feature a thin layer of tin on the surface, which provides excellent lubrication and reduces friction. Tinned pistons are lightweight and cost-effective, making them a popular choice for small engines that require high output power.

Advantages:

• Improved Corrosion Resistance: Tinning can improve the corrosion resistance of pistons.
• Reduced Friction: Tinning can reduce friction between the piston and cylinder wall resulting in reduced emissions.

Disadvantages:

• Cost: Tinning can add to the cost of piston manufacturing.
• Limited Applicability: Tinning may not be suitable for all engine types.

Oil-cooled pistons

Oil-cooled pistons are designed to maintain a stable temperature within the engine by directing oil flow to the piston head. These pistons feature an integrated oil cooling system, which helps regulate the engine’s temperature and prevents overheating. Oil-cooled pistons are commonly used in high-performance engines and racing applications.

Advantages:

• Improved Heat Dissipation: Oil cooled pistons can dissipate heat more effectively than other piston designs making it more reliable.
• Reduced Friction: Oil cooled pistons can reduce friction between the piston and cylinder wall.

Disadvantages:

1. Complexity: Oil cooled pistons can be more complex to manufacture and maintain.
2. Cost: Oil cooled pistons can be more expensive than other piston designs.

Two-piece pistons

Two-piece pistons are a unique type of piston that features a separate crown and skirt. The crown is the top part of the piston that comes into contact with the fuel, while the skirt is the bottom part that moves up and down within the cylinder. Two-piece pistons provide excellent heat dissipation, which helps prolong the piston’s lifespan. They are commonly used in high-performance engines and racing applications.

Advantages:

• Improved Flexibility: Two-piece pistons can allow for more flexibility in engine design. They can better accommodate engine modifications.
• Reduced Weight: Two-piece pistons can be lighter than other piston designs resulting into high performance.

Disadvantages:

• Cost: Two-piece pistons can be more expensive to manufacture due to their complex design.
• Durability: Two-piece pistons may be more prone to wear and tear than other piston designs leading to potential engine damage.

FAQ’s

Conclusion

In conclusion, the piston of a car is a vital component that plays a significant role in the engine’s functioning. The piston’s primary function is to convert the fuel’s energy into mechanical energy, which propels the car forward. There are several types of pistons available in the market, including taper piston, cam ground piston, special alloys, wire wound, autothermic, bimetal, cast steel, tinned, oil-cooled, and two-piece pistons.

Each type has specific features that cater to different needs and requirements. Therefore, it’s essential to choose the right piston for your car to ensure optimal performance and longevity. Proper maintenance and regular check-ups can also help increase the piston’s lifespan and prevent engine damage.