Classification of Engine: How do They work?

Looking for a detailed explanation of Types of Engines?

Then you landed in the right place. Here you will find different types of engines and their classifications in a simple and detailed manner.

So, I invite you to come with me and explore the fantastic journey of Engines with Engineers Rail.

Before I head on to the topic of the session, you will be amazed to know that you can download this whole article as types of engine pdf and types of engine ppt at the end of the article. So, Never forget to grab your freebies before hitting the back button.

First, let’s start with basics then we will head to further headlines down the road.

So, let’s get started…

What is Engine?

An engine is a device that transforms the chemical energy of a fuel into heat energy and uses this energy to produce mechanical work with the use of various components like a piston, connecting rod and crankshaft etc.

An engine is a complex unit in which different components are assembled together, and fuel is burned to produce power or energy. The engine converts the chemical energy of fuel into heat energy and then into mechanical energy.

Engines normally convert heat energy into mechanical work so they are also known as heat engines.

This figure will help you to understand more easily, Have a look-


Now, Let’s move to the types and classification of engines, where you will go through to the various classifications of the same.

Classification of Engine-

Engines are of mainly two types based on the where combustion takes place-

  1. Internal Combustion Engine (IC Engine)
  2. External Combustion Engine (EC Engine)

Internal Combustion Engine-

Internal combustion engines are those in which combustion takes place inside the engine. The heat generated due to combustion is used directly to exert pressure on the piston.

Every vehicle you can see on the road, all comes under the IC engines, where fuel burns inside the cylinder. For example, petrol engine or diesel engine.

Now, Let’s jump to the classification of IC engines or types of ic engines where we will classify the IC engine according to their terms.

So, here we go…

Classification of engine according to the type of fuel to be used-

  • Petrol Engine
  • Diesel Engine
  • Gas Engine

Petrol Engine– Petrol engines are those where petrol is used to fire the combustion chamber.

Diesel Engine– Diesel engines are those where Diesel is used to firing the combustion chamber.

Gas Engine- Gas engines are those where Gas or CNG is used to fire the combustion chamber.

Classification of engine according to the method of ignition-

  • Spark Ignition(SI) Engine
  • Compression-Ignition (CI) Engine

Spark Ignition(SI) Engine– Spark ignition engines are those where a spark plug is used to fire the engine. For example- Petrol engines

Compression-Ignition(CI) Engine– CI engines are those where combustion takes place due to compression of air and compression raises the temperature and pressure of air to match the auto or self-ignition temperature of diesel. For example- Diesel engines

Classification of engine according to the number of strokes per cycle-

  • Two Stroke Engine
  • Four Stroke Engine

Two-stroke Engine-  Two-stroke engines are those where suction and compression takes place two times to complete the single working cycle or to fully rotate the crank mechanism, known as two-stroke engines.

Four Stroke Engine- Four-stroke engines are those where suction and compression takes place four times to complete the cycle or reciprocating of piston four times to complete the single working cycle, known as a four-stroke engine. Four-stroke engines are known to be lesser pollutant engines than two-stroke engines.


Classification of engine according to the number of cylinders to be used-

  • Single Cylinder Engine
  • Multi-Cylinder Engine

Single Cylinder Engine- The engine, having a single cylinder and single-piston, is known as a single-cylinder engine. For example- Motorbikes.

single cylinder engine

Multi-Cylinder Engine- A engine, having more than one cylinder and one piston, can be called a multi-cylinder engine. For example- Four wheeler vehicles. The number of cylinders can be 4 to 6, and it can be maximized to 16 cylinders as of now.

Classification of the engine according to the cycle of operation-

  • Otto Cycle
  • Diesel Cycle
  • Dual Cycle

Classification of IC engine according to the speed of the engine-

  • Slow speed Engine
  • Medium speed Engine
  • High-speed Engine

Classification of IC engine according to the arrangement of the cylinder-

  • Horizontal cylinder Engines
  • Vertical cylinder Engines
  • V-type Engines
  • Radial types Engines

Classification of engine according to method of fuel injection-

  • Carburettor Engine
  • Fuel Injector Engine

Classification of engine according to valve arrangement-

  • Overhead valve mechanism
  • Side valve Engine

Classification of IC engine according to the method of the cooling cylinder-

  • Air-cooled Engine
  • Water-cooled Engine

Classification of engines according to their uses-

  • Stationary Engine
  • Automobile Engine
  • Marine Engine
  • Aero Engine

Now, Let’s move on to the external Combustion engine after knowing the types of engines in mechanical engineering, So here we go…

External Combustion Engine-

External combustion engines are those in which combustion takes place outside the engine. A boiler is used to generate high-pressure steam by combustion of fuel and further this steam is used as working fluid in a reciprocating engine or rotary turbine.

For Example- Steam engine or Steam turbine.

Now, Let’s look at the difference between IC engines and EC engines to understand the head to head differences in a single place.

So, Let’s dig in-

Difference Between Internal combustion Engine and External Combustion Engine-

Internal combustion EngineExternal Combustion Engine
Combustion takes place inside the cylinderCombustion takes place outside the cylinder
It starts quicklyIt doesn’t start quickly
These types of engines are compact in design and require less spaceThis type of engine is heavy and requires a large space
Overall efficiency is high, about 35-40%Overall efficiency is low, about 15-20%
The working pressure and temperature inside the cylinder is highThe working pressure and temperature inside the cylinder is low
Since the combustion of fuel takes place inside the cylinder, therefore these engines are noisier.Since the combustion of fuel takes place outside the cylinder, therefore these engines are smooth and silent running.
High thermal efficiencyLow thermal efficiency
The initial cost is lowThe initial cost is high
These engines are moveableStationary engines

For your further convenience, Here is the video guide to understanding How Engines works?



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What are the two classifications of an engine?

Ans. The main two classifications of an engine are-
Internal combustion engine
External combustion engine

What are the 5 engine systems?

Ans. The five engine systems are-
Cooling system
Ignition System
Fueling system
Lubricating system
Exhaust System

Why do we classify the engine in CC?

Ans. CC stands for Cubic centimetre, the more cc means more power. That’s why engines are classified in cc to indicate the power of the engine through CC.

What is called engine?

Ans. The process of converting a fuel’s chemical energy into heat energy and using that energy to create mechanical energy is known as an engine.

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