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Working of an Engine: Internal Combustion Engine Explained

Gaurav Verma is a creative an Automobile Engineer also a creative Technical writer.

What is an Engine?

Engine refers to a device which converts one form of energy to another."Heat engine is a modified form of engine used for transforming chemical energy of fuel into thermal energy and subsequently for producing work". Heat engines are classified in two forms based on where the combustion of fuel takes place.

  • Internal Combustion Engine (I.C. Engine)
  • External Combustion Engine (E.C. Engine)

In this article, we will discuss I.C. Engine.

I.C. Engine

I.C. Engine

Important Components of I.C. Engine.


It is where the fuel is burnt to generate power. It is made in such a way that it can withstand very high pressure and temperature. The piston reciprocates inside the cylinder.


The piston reciprocates inside the cylinder. The energy which develops due to the burning of fuel in the cylinder is transmitted to the crankshaft by connecting rod in the piston.

Piston ring

The piston rings are metallic rings inserted into the circumferential grooves provided at the top end of the piston. The piston rings maintain an airtight joint between the piston and the cylinder while reciprocating.


The energy transmitted by the piston is used to rotate the crankshaft. The crankshaft rotates along its axis which causes the connecting rod to oscillate.


It is the lower part of the engine, serving as an enclosure of the crankshaft and also as a sump for the lubricating oil.

Spark plug

It is used to generate a high-intensity spark for ignition of the air-fuel mixture in the cylinder.


Valves are the devices which control the flow of gases in and out of the engine cylinder. They are operated by valve operating mechanism.


Carburetor is used in petrol engine for proper mixture of air and petrol.


It is a heavy wheel mounted on the crankshaft of the engine. It minimizes the cyclic variation in speed by storing the energy during power stroke, and same is released during other stroke.




The inner diameter of the engine cylinder is called bore.


It is the linear displacement traveled by the piston when it reciprocates inside the cylinder. Stroke is twice the radius of the crank.

Compression Ratio

The ratio of engine cylinder volume to the clearances is called compression ratio.

Clearance Volume

It is the volume contained between the piston top and cylinder head when the piston is at the top dead center.

Stroke Volume

It is the volume displaced by piston in one stroke.

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Dead Centres

In vertical engines, top most position of the piston is called Top dead centre.when the piston is at bottom most position, it is called Bottom dead centre.

Indicated Power

The power produced inside the engine cylinder by burning of fuel is know as Indicated power of engine.

Brake Power

It is the power available at engine crankshaft for doing useful work. It is measured in dynamometer.

Mechanical Efficiency

It is defined as ratio of brake power and indicated power. It is an indicator of losses due to friction.

Thermal Efficiency

It is the conversation of heat energy by actual combustion of the fuel into power output. It is ratio of work done to heat supplied.

Internal Combustion Engine

Internal Combustion Engine

Four Stroke Engine

The piston performs four strokes to complete one cycle. The four different strokes are

  • Suction stroke
  • Compression stroke
  • Power stroke
  • Exhaust stroke

Suction Stroke

During this stroke, inlet valve opens and exhaust valve is closed. As the piston moves, the volume in cylinder increases, while simultaneously the pressure decreases.

This creates a pressure difference. Due to this the fuel and air mixture will enter into the cylinder.

Compression Stroke

Both the inlet valve and exhaust valve are closed. As this stroke is been performed, the fuel and air mixture will be compressed.

Near the end of this stroke, fuel and air mixture is ignited by electric spark given out by spark plug. The combustion of fuel releases the hot gases.

Power Stroke

The high pressure and high temperature forces the piston to perform this stroke. The engine produces mechanical power during this stroke.

Near the end of this stroke, the exhaust valve opens.

Exhaust Stroke

During this stroke, the exhaust valve opens and the motion of piston pushes the exhaust gases out of the cylinder.

Again the inlet valve opens and a new cycle starts.

Two Stroke Engine

All the processes in the two stroke engine are completed in two strokes. In this engine, suction of fuel and air mixture into the cylinder will not take place in a separate stroke.

First Stroke

At the beginning the piston is at The dead centre. The electric spark ignites the compressed fuel. The combustion releases hot gases which increases the pressure and temperature of the cylinder. The high pressure force the piston downwards. The piston performs the power stroke till it uncovers the exhaust port. The combustion gases escape through the exhaust port. The piston uncovers the transfer port and fresh fuel flows from the crankcase into the cylinder. The fresh fuel which enters the cylinder pushes the burnt gases. This process is called scavenging.

Second Stroke

In this stroke the piston returns to THE dead centre. When it covers the transfer port the supply of fuel stops and then when it moves further up it covers the exhaust port completely stops the scavenging. Further upward motion of the Piston compresses the charge in the cylinder. After the piston reaches THE dead Centre the first stroke repeats again.

Advantages of I.C. Engine

  • Compact size and more efficient
  • Low initial cost
  • Easier and quick starting of these engines
  • Suitable for mobile applications
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© 2017 Gaurav Verma


Timothy Maloba from mumias on May 24, 2019:

Very good article

WheelScene from U.S.A. on October 26, 2017:

You should talk about a Tesla / Electric motor, maybe diesel too! Great article thanks for sharing.

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