what is the function of piston in ic engine

What is Piston

The piston transfers combustion pressure to the connecting rod and crankshaft. It should hold the piston ring and piston pin while working on the cylinder. Pistons are usually made or forged from an aluminum alloy. Cast pistons are relatively smooth and are used in slow-speed, low-performance engines. function of piston in ic engine Forged pistons are commonly used in today’s fuel-injected, turbocharged and diesel engines. These engines expose the pistons to very high compressive loads, which can break cast aluminum pistons.

The piston must withstand incredible punishment under extreme temperatures.

Examples of conditions a piston must encounter at normal highway speeds include:

Function of piston in ic engine 

Pistons play an important role in automobile engines, including spark ignition gasoline engines and compression ignition diesel engines. The process of these two internal combustion engines is different but they use pistons. The functions of a piston in an automobile engine are given below:

  • The main function of the piston is to transfer the power output of a small burst of gas in the cylinder to the crankshaft. function of piston in ic engine It provides rotational motion to the flywheel.
  • It moves forward so that the gases are compressed and explode as it moves backward.
  • The piston has a pin called the piston pin which allows the gas in the chamber to escape.
  • A connecting rod attached to the bottom of the piston allows the mechanical work to be changed.
  • Pistons help move the air-fuel mixture during the combustion cycle.
  • Pistons use oil control rings to help control the flow of oil to the cylinder walls.
  • As the piston moves from the top to the bottom of the cylinder (or vice versa), function of piston in ic engine  it accelerates from a stop to about 60 mph at the midpoint, and then slows to a stop again. It does this about 80 times per second.
  • The piston must with stand a pressure of 1,000 psi in its head

Temperatures above 600°F.

The structural components of a piston are the head, skirt, ring grooves, however, not all pistons look like the normal piston shown here. Some have different shaped heads.

The piston head is the top of the piston and is exposed to combustion heat and pressure. function of piston in ic engine This field must be dense enough to withstand these forces. The working volume should match the combustion chamber volume for complete combustion.

Piston material

Cast iron can earliest material used to make pistons. However modern machines benefit from lighter materials for mechanical balance. Good pistons should be able to withstand the engine’s combustion temperatures. Alloys such as Y alloy and aluminum can particularly used to achieve such properties. function of piston in ic engine Pistons can  made from aluminum alloy with casting process.

Some pistons used in racing vehicles require higher strength and fatigue life, which can why they can forged. function of piston in ic engine Billet pistons can also used in racing engines because they can independent of the size and architecture of available forges, allowing for last-minute design changes. However, it is usually invisible to the naked eye.

Types of pistons

Below are three types of pistons:

 function of piston in ic engine

  • Dish piston: A dish piston can shaped like a plate with slightly curved outer edges. function of piston in ic engine It is easy and simple and gives less hassle to engineers. It can often used in boosted applications that do not require a high-lift camshaft or high compression ratios.
  • Flat-top piston: The flat-top type of piston has a flat top. It has less surface area, which allows it to generate more power. This is perfect for creating efficient combustion. Flat-top pistons produce more detonation in the chamber, but compression may be too high for small combustion chambers.
  • Dome Piston: The concept of a dish piston is the exact opposite of a dish type. function of piston in ic engine Middle bubble to increase surface area remaining on top of piston. Well, more surface area means less compression, while more compression means more power generation. The combustion chamber has a maximum limit to what it can handle, so reducing the compression ratio is the best way to avoid breaking the engine.

Function of piston

what is the function of piston in ic engine

  • Piston skirt is the edge of the piston below the end ring. Without a skirt, the piston can bend and jam in the cylinder. A slipper skirt can formed when a portion of the piston skirt can removed below the piston ends. The slipper skirt provides clearance between the piston and the crankshaft counterweight. This allows the piston to slide into the cylinder without hitting the crankshaft. A straight skirt with a flat bottom, this style is no longer common in automotive engines
  • Piston ring grooves can machined slots in the piston for the piston rings. function of piston in ic engine The top two grooves hold compression rings. The lower piston groove holds the oil ring.
  • The piston oil hole in the lower ring groove allows oil to pass through the piston and into the cylinder wall.
  • The area between and above the piston ring lands ring groove. They separate and support the piston rings as they slide over the cylinder.
  • Piston boss is a reinforced part around the piston pin bore. The piston pin must be strong enough to withstand heavy loads.


  • The piston pin can drilled through the pin boss for the piston pin. function of piston in ic engine It is slightly larger than a piston pin.
  • The piston pin, also known as the wrist pin, allows the piston to oscillate on the connecting rod. The pin fits through holes in the small end of the piston and connecting rod. Piston clearance is the clearance between the edges of the piston and the cylinder wall. The clearance allows a lubricant film to form between the piston and the cylinder. It also allows the piston to expand as it heats up.
  • The cam-ground piston (Figure 3-15) looks slightly outward when viewed from above. function of piston in ic engine The piston can machined to a diameter of a few thousandths of an inch perpendicular to the piston pin centerline.
  • Cam grinding can done to compensate for different expansion rates of the piston due to differences in metal wall thickness. As the piston can heated by combustion, the thick can  surrounding the pin boss expands parallel to the piston piston pin.
  • Cold cam-ground pistons have perfect piston-to-cylinder clearance. Excessive clearance will cause the unextended piston to slam, flop sideways, and knock into the cylinder. However, the cam-ground piston does not fit very tightly in the cylinder when heated to full operating temperature.
  • Piston taper can also used to maintain proper piston-to-cylinder clearance. function of piston in ic engine The top of the piston is slightly smaller than the bottom. As the piston head is hotter than the skirt, it expands further. Piston taper makes the piston roughly equal at top and bottom at operating temperature.
Piston temperature distribution

Typical values of temperature in different parts of a cast iron piston. function of piston in ic engine It can noted that the maximum temperature occurs at the center and the temperature is lowest at the bottom of the skirt. Poor design can lead to thermal overload of the piston in the center of the crown. The temperature difference between the outer edge of the piston and the center of the crown is responsible for the flow of heat in the annular belt through the path provided by the metal part of the crown.

Therefore, it is necessary to increase the thickness of the crown from the center to the outer edge to provide more cross-sectional passage for increased heat content. The path length should not be too long or the thickness of the crown cross-section should not be too small for heat flow. function of piston in ic engine This will increase the temperature in the center of the crown and cause an excessive temperature difference between the crown and the outer edge of the piston.

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cups can installed in the diesel engine piston head. function of piston in ic engine The shape of the combustion cup moves the fuel in a turbulent pattern as it enters the combustion chamber, allowing more intense mixing for efficient combustion. Two common combustion cup designs are the sombrero cup and the turbulence cup. Piston rings seal the gap between the outside of the piston and the cylinder wall. They should prevent combustion pressure from entering the crankcase. function of piston in ic engine They must prevent oil from entering the combustion chamber.

Most pistons use three rings, two top compression rings and one bottom oil ring. Compression rings prevent detonation (prevents combustion pressure from leaking into the engine crankcase). Diesel engine pistons typically use a four-ring design because they are more prone to flying. function of piston in ic engine A four-ring piston has three compression rings at the top, followed by an oil control ring. This happens due to the very high pressure generated during the power stroke.

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