How Does an Internal Combustion Engine Work?

For most people, a car is a thing they fill with gas that moves them from point A to point B. But have you ever stopped and thought, How does it do that? What makes it move? Unless you have already adopted an electric car as your daily driver, the magic of how comes down to the internal combustion engine—that thing making noise under the hood. But how does an engine work, exactly?

Specifically, an internal combustion engine is a heat engine in that it converts energy from the heat of burning gasoline into mechanical work, or torque. That torque is applied to the wheels to make the car move.

And unless you are driving an ancient two-stroke Saab (which sounds like an old chainsaw and belches oily smoke out its exhaust), your engine works on the same basic principles whether you’re wheeling a Ford or a Ferrari.

What is an internal combustion engine?

In simple terms, combustion, also known as burning, is the process of releasing energy from a mix of fuel and air.

In an internal combustion engine (ICE), the ignition and combustion of the fuel occurs within the engine itself. The engine then partially converts the energy from the combustion to work. The engine consists of a fixed cylinder and a moving piston.

When the combustion gases expand, they push the piston, which then rotates the crankshaft. Ultimately, this motion is transferred to the wheels of the vehicle through a set of gears in the powertrain.

There are two types of internal combustion engines commonly used today: spark-ignition gasoline engines and compression-ignition diesel engines. Most of these engines operate on a four-stroke cycle, which means four piston strokes are needed to complete one cycle. This cycle includes four distinct processes: intake, compression, combustion and power stroke, and exhaust.

Spark-ignition gasoline engines and compression-ignition diesel engines differ in how they supply and ignite the fuel. In a spark ignition engine, the fuel is mixed with air and drawn into the cylinder during the intake process.

Once the piston compresses this fuel-air mixture, a spark ignites it, causing combustion. The expanding combustion gases then push the piston during the power stroke.

On the other hand, in a diesel engine, only air is drawn into the engine and compressed. Diesel engines inject the fuel into the hot compressed air at a controlled rate, which causes it to ignite.

internal combustion engine

Read More: What is an External Combustion Engine?

Invention Of Internal Combustion Engine

The first commercially successful internal combustion engine was created by Étienne Lenoir around 1860, and the first modern internal combustion engine, known as the Otto engine, was created in 1876 by Nicolaus Otto.

In 1859, Belgian Jean Joseph Etienne Lenoir built a two-stroke internal combustion engine, which was fueled by coal gas and ran on a mixture of air and gas.

Later, in 1886, Benz began the first commercial production of motor vehicles with an internal combustion engine, in which a three-wheeled, four-cycle engine and chassis formed a single unit.

How does an internal combustion engine work?

In an internal combustion engine, it’s like this: fuel burns inside the engine itself. You’ll find this type of engine not just in cars, but in most other motor vehicles too. The engine works in a bunch of steps that keep happening over and over again. Look at the Figure below to see how it goes.

  • First, a mix of fuel and air gets sucked into a cylinder through a valve. Then the valve closes.
  • Next, there’s a piston inside the cylinder that moves up and squeezes the fuel-air mix. The mix gets squished and gets really pressurized and hot.
  • After that, a spark from a spark plug sets the fuel-air mix on fire. Boom! It burns up like crazy inside the closed cylinder.
  • The pressure from the hot gases from burning pushes the piston down.
  • Then the piston moves back up, and it kicks out the leftover exhaust gases through another valve.
  • The piston goes down again, and the whole cycle starts again.

That’s how the engine does its thing. It turns the heat energy into kinetic energy, or the energy of something moving—the piston moving up and down, in this case.

How Energy from the Engine Turns the Wheels?

Ever wondered how a car’s engine makes those wheels spin? Let’s break it down for you:

  • Inside the engine, there’s a mix of fuel and air that goes boom in a closed cylinder, making a piston move up and down.
  • That piston is like the engine’s muscle, connected to a crankshaft. It’s this crankshaft that turns the piston’s up-and-down motion into the spinning motion we need.
  • Now, the crankshaft is linked to a driveshaft, and this bad boy is in charge of sending power to the wheels of the car.
  • The driveshaft connects to something called a differential. Think of it as a traffic cop that directs the power to each wheel.
  • As those pistons keep doing their thing, they rotate the crankshaft. This power then goes through the transmission and eventually makes the wheels turn.

In cars with manual transmissions, there’s a cool thing called a flywheel. It keeps the power flowing smoothly since the engine only delivers power during certain strokes. The flywheel stores up rotational energy and releases it when needed.

So, to sum it all up, the engine is connected to the wheels through a bunch of mechanisms that change the piston’s up-and-down motion into rotational motion. This power gets transmitted through the driveshaft and differential, making those wheels spin and your car goes vroom!

Applications of internal combustion engines

Internal combustion engines are the most broadly applied and widely used power-generating devices currently in existence. Examples include gasoline engines, diesel engines, gas-turbine engines, and rocket-propulsion systems.

IC engine has many applications like,

  • Gasoline Engines: Automotive, Marine, Aircraft
  • Gas Engines: Industrial Power
  • Diesel Engines: Automotive, Railways, Power, Marine
  • Gas Turbines: Power, Aircraft, Industrial, Marine

Classification Of Internal Combustion Engines

There are two kinds of internal combustion engines currently in production: the spark ignition gasoline engine and the compression ignition diesel engine. Most of these are four-stroke cycle engines, meaning four piston strokes are needed to complete a cycle.

IC engines can be classified on the basis of fuel used, thermodynamic cycle, type of ignition, type of cooling system, cylinder arrangement, method of charging, etc.  Now we study it in detail.

1) According To the Cycle Of Operation:

We know IC engines convert chemical energy into mechanical energy in cyclic operation. There are many thermodynamic cycles e.g. Carnot cycle, Otto Cycle, Diesel Cycle, Rankine cycle, etc.

IC engines work on three cycles Otto cycle and Diesel cycle and the Dual cycle. So according to it, IC engines can be classified into the following types.

1. Otto Cycle Engine:

It is also known as a spark-ignition engine or constant volume heat addition engine, Petrol engine, etc. In this cycle heat addition (fuel burn) and rejection (exhaust) takes place at constant volume and expansion and compression take place at isentropic. These engines give low power at high speed.

2. Diesel Cycle Engine

This is known as a compression-ignition engine, diesel engine, constant-pressure engine, etc. In this cycle heat addition (fuel burn) takes place at constant pressure and heat rejection takes place at constant volume.  This engine gives high power at a low speed.

3. Duel Cycle Engine:

The dual cycle is a combination of the Otto cycle and the diesel cycle. In this engine, heat addition takes place both at constant volume and constant pressure in some ratio.

Some engines work on the Stirling cycle and Ericsson cycle but these are not used commercially.

2) According To The Type Of Fuel Used:

Most of us know about these engines. These are petrol engines and diesel engines. Nowadays gaseous fuel like LPG, CNG, hydrogen, etc. is also used in IC engines. These engines are called non-traditional engines.

3) According To The Method Of Charging:

The charging means how the admission of the fuel-air mixture takes place. This can be classified as follow.

1. Naturally aspirated engine:

In this engine, admission of the air-fuel mixture (SI Engine) or air alone (CI engine) takes place due to pressure differences inside the cylinder and atmospheric pressure.

2. Supercharged Engines:

In this engine, a separate compressor is used to the admission of charge inside the cylinder. This compressor is run using engine power (connected with the crankshaft with belt drive).

3. Turbocharged Engine:

This engine uses a turbine that draws air into the cylinder and runs by using exhaust gas power. It is also like supercharging but the compressor is run by a turbine which is rotated by exhaust gases.

4) According To Ignition:

In IC engines ignition of charge can take place in two ways. In the first one, a separate spark plug or any other device is used to ignite the fuel (Spark Ignition Engine) and the other one is fuel ignited due to heat generated during compression or fuel (Compression Ignition Engine).

So according to these methods, two engines are available spark-ignition engine or SI engine (Petrol Engine) and compression ignition engine or CI engine (Diesel Engine).

5) According To A Type Of Ignition System:

In petrol engines, we used a spark plug to ignite the fuel. This spark at the spark plug, produce by an ignition system. According to the ignition system, two types of engines are there. The first one is the battery ignition engine (which uses a battery to generate a spark) and another one is a magneto ignition engine (which uses a small generator to generate a spark).

6) According To the Design Of the Engine:

1. Reciprocating Engine:

In this type of engine, a piston is used which moves in reciprocating motion by using pressure force generated by the burning of fuel. The crankshaft converts this reciprocating motion into rotary motion. Most automobile engines are reciprocating type.

Read More: What is Reciprocating Engine?

2. Rotary Engine:

In a rotary engine, a rotor is used. The pressure force generated by the burning of fuel is exerted on this rotor, which further rotates the wheel. The Wankel engine is one type of rotary engine. These engines are currently not used in automobile engines.

7) According To Cooling:

Two types of cooling are used in IC engines, air cooling, and water cooling. So the engines are air-cooled engines or water-cooled engines. Both these cooling systems have their own advantages, which we will discuss later. Engine oil is also serving as a cooling medium.

8) According To the Stroke Of the Engine:

We know that the stroke is the maximum distance a piston can travel inside a cylinder or between TDC to BDC. If an engine moves from TDC to BDC, it is called one stroke. If it returns to BDC it is called two strokes. A crankshaft makes one rotation in two strokes. According to it, three types of engines have been invented.

1. Two-stroke Engine:

In this engine, the crankshaft makes one rotation in one power stroke. This engine gives more power compared to others. It is used in shooters, ships, generators, etc.

Read More: What is Two-stroke Engine? and What is a Four-stroke Engine?

2. Four-stroke engines:

This engine gives two crankshaft rotations in one power stroke. They give low power but high efficiency. It is used in cars, trucks, bikes, etc.

3. Six-stroke engines:

These engines are in the development process. As the name implies, it will give three crankshafts rotation in one power stroke.


What is an internal combustion engine work?

An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit.

Who Invented The Internal Combustion Engine?

In 1823, Samuel Brown patented the first internal combustion engine to be applied industrially in the U.S.; one of his engines pumped water on the Croydon Canal from 1830 to 1836. The first commercially successful internal combustion engine was created by Étienne Lenoir around 1860 and the first modern internal combustion engine was created in 1876 by Nicolaus Otto. In 1872, American George Brayton invented the first commercial liquid-fueled internal combustion engine.

How does an internal combustion engine work?

The engine consists of a fixed cylinder and a moving piston. The expanding combustion gases push the piston, which in turn rotates the crankshaft. After the piston compresses the fuel-air mixture, the spark ignites it, causing combustion. The expansion of the combustion gases pushes the piston during the power stroke.

What are the application of Internal combustion Engines?

IC engine has many applications like:
Gasoline Engines: Automotive, Marine, Aircraft
Gas Engines: Industrial Power
Diesel Engines: Automotive, Railways, Power, Marine
Gas Turbines: Power, Aircraft, Industrial, Marine

Leave a Comment