How Does an Internal Combustion Engine Work?

Engine Components

An internal combustion engine mixes air with fuel and burns the resulting mixture to produce motion. Its rotation then does valuable work, such as turning a car’s wheels. This article explains everything about the workings of these engines, starting with the definition.

What is an Internal Combustion Engine?

An internal combustion engine is a heat engine where combustion (fuel burning to release energy) occurs within itself. It contrasts with the external combustion type, which burns the fuel source externally.

IC engines generally consist of upper sections, called the cylinder heads, and lower sections, called cylinder blocks. The head contains valves and ignition components. The lower section houses the crankshaft, piston, and cylinders.

IC engines are available in different configurations, mainly based on the number of cylinders and their layout. They can be single-cylinder types and up to 8 cylinders or more. By cylinder arrangements, the types of this engine include:

  • Inline or Straight – the cylinders are arranged to form a straight line, one after the other
  • V Design – they have the cylinders arranged to form a V-shape
  • Flat Layout – the cylinders are placed horizontally on each side of the crankshaft
The working of the engine working illustrated.
The working of the engine working illustrated

How Does an Internal Combustion Engine Work?

The internal combustion engine working principle is based on converting chemical energy into mechanical energy. The chemical energy is stored in fuel, typically diesel or gasoline.

When burned in the presence of air, the fuel releases energy in heat, creating rapidly expanding gases that move mechanical components called pistons.

The up-and-down motion of the pistons moves rods and transfers the motion to the crankshaft. The crankshaft turns, and its revolution is used to operate an external mechanism, such as vehicle transmission.

To ensure a smooth operation, the pistons fire in turns. A timing system ensures the valves on each cylinder open at the appropriate time.

The crankshaft has weights that balance piston movements, while a flywheel mounted externally to the block ensures constant revolutions. The flywheel also meshes with the starter to set the cylinders firing.

IC engine process strokes
IC engine process strokes

Internal Combustion Engine Process

A single combustion cycle, called a stroke, sees the piston travel up or down. Most IC engines today are four-stroke types. Their operation is broken into these four steps: intake, compression, combustion, and exhaust stroke.

Intake Stroke

The intake stroke is called so when the two most essential combustion ingredients — fuel and air— enter the cylinders.

  • Air enters the intake manifold after being filtered to remove contaminants.
  • Here, it mixes with fuel, which has also been filtered to eliminate pollutants.
  • At the same time, the camshaft moves parts to open the intake valves
  • The piston descends in the cylinder, creating a low-pressure region
  • The mixture then gets sucked into the cylinder

Compression Stroke

The combustion process can begin with the air and fuel in the cylinder. But only after the mixture has been compressed can it be prepared for a powerful explosion.

  • The camshaft now closes the intake valves
  • The piston comes back up, compressing the mixture and increasing its temperature
  • This provides the required optimum conditions for compression and maximum release of energy

Power Stroke

The mixture is now compressed, heated, and ready for ignition. What happens next depends on whether the engine uses gasoline or diesel.

  • In a diesel engine, the intense pressure created in the mixture when the piston ascends causes the air-fuel blend to self-ignite
  • In a gasoline engine, electrical components called spark plugs ignite the fuel
  • The fuel burns aggressively, releasing energy and producing expanding gases
  • The rapidly expanding gases push the piston down with tremendous force
  • A rod connected to the piston transfers this movement to the crankshaft, causing it to turn

Exhaust Stroke

The spent mixture now contains the products of combustion. These must exit the cylinder to create space and conditions for the next cycle.

  • The piston now moves back up, forcing the spent gases to the top
  • Meanwhile, the camshaft has opened the exhaust valves
  • The exhaust manifold collects the products of the combustion process before their exit through a single pipe called the exhaust pipe, with a muffler to reduce the noise
Engine's  Combustion & Components
Engine’s Combustion & Components

How Efficient Are Internal Combustion Engines?

IC engines cannot be said to be efficient. Most barely convert 50% of the energy of combustion into mechanical energy. However, modern technologies have enabled the production of engines with higher efficiency.

Embedded electronics precisely time and control various processes, such as fuel injection and valve timing, making the combustion more effective.

At the same time, technologies that increase power while reducing emissions, such as turbocharging and the action of the catalytic converter are being included in the engine operation. These and proper maintenance ensure your car performs optimally to deliver the most power.

Engine cooling system
Engine cooling system

Internal Combustion Engine Cooling

The internal combustion engine temperature can rise very high, which can be disastrous if not adequately addressed. All IC engines are, therefore, made from a material that not only withstands extreme heat but also dissipates it.

More importantly, they have a channel network that circulates coolant, a special liquid containing water and antifreeze. Its function is to absorb heat from the various components and dissipate it in the radiator.

The radiator comprises an elaborate network of thin tubes and cooling fins. Coolant passes through these, losing heat to the air before returning to the engine. A fan placed near the radiator blows air to speed up the cooling.

A pumping device called a water pump ensures the efficient circulation of the coolant, while a thermostat helps regulate its temperature based on the engine’s requirements.

The Lubrication System Works In An Engine
The Lubrication System Works In An Engine

Internal Combustion Engine Lubrication

The moving parts require constant lubricating, or friction could cause them to heat up to heat up quickly and seize or experience untold wear.

Passages called oil galleries supply lubricating oil to the various parts. In addition to lubrication, the oil serves several other functions, like sealing and cooling.

An oil pump keeps the oil flowing as needed while the “oil filter” rids it of contaminants. When not circulating, the oil sits in the oil pan or sump, a reservoir in the engine’s lowest section.


You now know how internal combustion engines work, the various parts that make them, and their cooling and lubrication systems. As you’ve learned, its operation depends on many components, some of which wear down over time and require changing.

WanTuo is a professional engine parts manufacturer and supplier. Our extensive products range includes crankshafts, camshafts, cylinder heads, pistons, valve components, and may more. Contact us today to view our catalog.


I'm Louis, a seasoned writer specializing in auto parts, particularly the science behind components like cylinder heads and pistons. With over a decade of experience and a background in mechanical engineering, my articles reflect a commitment to professionalism, blending technical insight with engaging content.

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