Four Stroke Engine: Working, Parts, Diagram, Advantages and Real-Life Applications

The four stroke engine is one of the most commonly used engines in vehicles and machines today. It converts the energy of fuel into mechanical power through four separate piston strokes. This design makes the engine fuel-efficient, reliable, and suitable for everyday use. 

This article provides a detailed explanation of what is four stroke engine, its parts, working cycle, advantages, and the difference between petrol and diesel engines.

Table of Contents

• What Is a Four Stroke Engine
• Main Components of a Four Stroke Engine
• Four Stroke Engine Working Cycle
• Important Advantages of Four Stroke Engine
• Real-Life Applications of Four Stroke Engine
• Frequently Asked Questions on Four Stroke Engine

What Is a Four Stroke Engine

A four-stroke engine is an internal combustion engine that generates power by completing four separate piston strokes inside a cylinder. These four strokes work together to complete one full operating cycle. During this process, the crankshaft makes two complete rotations (720°).

The four strokes are,

• Intake (Suction)
• Compression
• Power (Combustion)
• Exhaust

In each stroke, the piston moves either from the Top Dead Centre (TDC) to the Bottom Dead Centre (BDC) or back again. This repeated movement helps convert the energy released by burning fuel into mechanical power.

Interestingly! The four stroke engine was first developed by the German engineer Nikolaus Otto in the late 19th century. His invention, known as the Otto cycle, became the foundation of most modern petrol engines.

Today, the four stroke engine is widely used because it offers smooth performance, better fuel efficiency, and a longer operating life. You can find it in many vehicles and machines, including:

• Cars
• Motorcycles
• Tractors
• Buses
• Lawn mowers
• Generators
• Boats
• Small aircraft

Main Components of a Four Stroke Engine

Each component has a specific function, and together they make the engine run efficiently.

Component	Function
Cylinder	The cylinder is the space where the piston moves and fuel combustion takes place. It is made from strong metals such as cast iron or aluminium alloy to handle high pressure and heat.
Piston	The piston moves up and down inside the cylinder. It receives the force produced during combustion and transfers it to the connecting rod.
Piston Rings	These rings fit around the piston. They prevent gas leakage, control engine oil on the cylinder walls, and help remove heat from the piston.
Connecting Rod	The connecting rod joins the piston to the crankshaft. It transfers the piston's movement into rotational motion.
Crankshaft	The crankshaft converts the piston's up-and-down movement into rotary motion that powers the vehicle or machine.
Flywheel	The flywheel stores rotational energy and helps the engine rotate smoothly between power strokes.
Intake Valve	This valve opens to allow fresh air or the air-fuel mixture to enter the cylinder.
Exhaust Valve	It opens after combustion to release the burnt gases from the cylinder.
Spark Plug( four stroke petrol engine)	The spark plug produces an electric spark that ignites the compressed air-fuel mixture in a four stroke petrol engine.
Fuel Injector(four stroke diesel engine)	In a four stroke diesel engine, the fuel injector sprays diesel into highly compressed hot air, causing automatic ignition.

The fact is that even though these parts are different in shape and function, they all work together to complete the four engine strokes smoothly.

Four Stroke Engine Working Cycle

Moving ahead, let's see how a four stroke engine works. It completes one operating cycle through four piston strokes, while the crankshaft makes two full rotations (720°).

Intake (Suction) Stroke

The piston moves from TDC to BDC. The intake valve opens, allowing fresh air-fuel mixture to enter in a four stroke petrol engine, while only air enters in a four stroke diesel engine. The exhaust valve remains closed.

Compression Stroke

The piston moves back from BDC to TDC with both valves closed. This compresses the air or air-fuel mixture, increasing its pressure and temperature for efficient combustion.

Power (Combustion) Stroke

Just before the piston reaches TDC, combustion takes place. In a four stroke petrol engine, the spark plug ignites the mixture, while in a four stroke diesel engine, diesel fuel ignites due to high compression. The expanding gases push the piston downward and produce power.

Exhaust Stroke

The piston moves from BDC to TDC. The exhaust valve opens, allowing burnt gases to leave the cylinder. The engine is then ready for the next cycle.

Important Advantages of Four Stroke Engine

The four stroke engine is widely used around the world. Although it completes one power cycle in four strokes, it offers better efficiency, smoother performance, and greater durability than many other engine types. 

Some of the main advantages of a four stroke engine are,

• Better fuel efficiency: It burns fuel more completely, reducing fuel consumption.
• Lower emissions: Efficient combustion produces less smoke and fewer harmful gases.
• Quieter operation: It runs more smoothly and creates less noise than a two-stroke engine.
• Longer engine life: A separate lubrication system reduces wear and increases durability.
• Reliable performance: It delivers steady power for long-distance and regular use.
• Lower oil consumption: Engine oil is stored separately, so it is not mixed with the fuel during operation.

The fact is that these advantages make the four stroke engine the preferred choice for cars, motorcycles, tractors, generators, and many other machines.

Real-Life Applications of Four Stroke Engine

Moving further, let's see where the four stroke engine is commonly used. Due to its fuel efficiency, durability, and smooth operation, it powers many vehicles and machines.

Some common applications include,

• Cars and Motorcycles: Used in most modern petrol and diesel vehicles.
• Trucks and Buses: Four stroke diesel engines provide high torque for heavy loads.
• Tractors and Construction Equipment: Used in farming and heavy machinery.
• Generators: Produce electricity during power outages.
• Lawn Mowers and Water Pumps: Compact four-stroke engines are reliable and easy to maintain.
• Boats and Light Aircraft: Used for efficient and dependable performance.

The fact is that the four stroke engine is one of the most widely used engine types because it offers reliable performance across a wide range of applications.

The four-stroke engine works through four piston strokes, intake, compression, power, and exhaust to produce mechanical power. We also covered what is four stroke engine, its main components, working cycle, four stroke petrol engine diagram, the working of a four stroke petrol engine and a four stroke diesel engine, along with its advantages and applications.