Four Stroke Engine: Diagram, Parts, Working & Difference

In this post, we will going to learn what is four stroke engine and how it works. This article will also go over the parts, comparison, and uses.

What is Four Stroke Engine?

An internal combustion engine with four different piston strokes (intake, compression, power, and exhaust) is known as a four-stroke engine. In a four-stroke engine, the crankshaft must turn twice (7200) to complete an working cycle.

In these types of engines, the piston rotates the crankshaft four times per revolution. The piston travels along the cylinder in four directions in a four-stroke engine: suction, compression, power, and exhaust.

In 1876, Nicolaus Otto invented the first four-stroke engine. It uses the Otto cycle and is also known as the ‘Otto cycle engine’.

In automobiles, trucks, trains, light aircraft, and motorcycles, four-stroke engines are the most commonly used internal combustion engines.

Parts of Four Stroke Engine

Following are the important parts of a four stroke engine:

#1 Inlet and Exhaust Valve

Inlet valves allow fresh air to enter into the cylinder and mix it with fuel. The exhaust valves simultaneously remove the consumed air-fuel combination from the cylinder and replace it with fresh air.

#2 Cylinder Head

The cylinder head is a separate cast component that covers the top of the cylinder. The cylinder head is attached to the cylinder block via studs.

#3 Cylinder Block

The engine block is important to the function of the car since it supports engine components. It transmits heat from friction to the coolant and the atmosphere while also supporting the lubricating circuit and auxiliary devices like the alternator.

#4 Spark Plug

A spark plug is a component that fits into the cylinder head of an internal combustion engine. The spark plug consists of two electrodes separated by an air gap, where current from a high-tension ignition system discharges, creating a spark that ignites the mixture of air and fuel.

#5 Crankshaft

A crankshaft is a mechanical component that converts reciprocating action into rotating motion. The crankshaft is a revolving shaft with one or more crankpins that are driven by connecting rods and pistons.

#6 Piston

The piston is a moving component of the combustion chamber. Its function is to convert the energy created during combustion into mechanical work.

#7 Connecting Rod

Connecting rods are engine components that connect the piston to the crankshaft and function as lever arms. These are typically built of cast aluminum alloy and are intended to endure dynamic loads from combustion and piston movement.

#8 Crankcase

The housing that encloses the crankshaft of a piston engine is called the crankcase. It serves as a sump for lubricating oil. The crankcase is usually built into the engine block in modern engines.

#9 Cylinder

The cylinder in a reciprocating engine is the area through which a piston moves. The inside surface of the cylinder is made of a thin metallic lining.

Working of Four Stroke Engine

This engine works in four stages: suction, compression, power, and exhaust.

#1 Suction or Intake Stroke

The air-fuel mixture enters the combustion chamber during the intake stroke. During this stroke, the piston travels from TDC (top dead center) to BDC (bottom dead centre).

This piston movement creates a low-pressure area in the cylinder. After BDC, the inlet valve needs to open by a few crankshaft rotations. The intake valve is then closed, sealing the air-fuel mixture inside the cylinder.

#2 Compression Stroke

Air-fuel combination that has been kept inside the cylinder is compressed during the compression stroke. During the stroke, the piston travels from BDC to TDC, compressing the air-fuel combination.

The piston moves with the help of the flywheel’s momentum. When the charge ignites, more energy is produced due to the compression of the air-fuel mixture.

In the combustion chamber, the charge is the volume of compressed air and fuel ready to ignite. The intake and exhaust valves must be fully closed to seal the cylinder, resulting in compression.

#3 Power or Combustion Stroke

When a spark plug is used to ignite the compressed air-fuel mixture, the power stroke begins. The combustion process occurs when fuel chemically combines with oxygen in the atmosphere, releasing heat as a result.

Due to this, the heated expanding gasses move the piston head away from the cylinder head. During this stroke, the intake and output valves are both closed.

#4 Exhaust Stroke

The power stroke ends when the piston reaches back to the front (BDC), at which point exhaust gasses enter the cylinder.

During this, the exhaust valves open, and the inertia of the flywheel and other moving parts causes the piston to return to TDC, forcing the exhaust gas to exit the engine through the open exhaust valves.

The piston reaches TDC at the end of the exhaust stroke, completing one operational cycle.

Difference Between Two Stroke Engine and Four Stroke Engine

The comparison between a two-stroke and a four-stroke engine is shown in the table below.

Based On	Four-stroke Engine	Two-stroke Engine
Structure	This engine has a complex structure and is expensive to maintain.	Its structure is simple, easy to repair, and inexpensive.
Noise Produce	The four-stroke engine generates less noise.	Two-stroke engines make greater noise.
Strength	This engine does not wear out rapidly because it operates at lower RPMs.	This engine wears out quickly as it runs at higher RPMs.
Cooling Type	A four-stroke engine can be air or liquid cooled.	Two-stroke engine uses air cooling.
Torque Produce	It delivers higher torque at lower RPMs.	It generates more torque at higher RPMs.
Weight of Engine	Four-stroke engines are usually heavier in weight.	Two-stroke engines are often lighter in weight.
Uses	This type of engine is mostly utilized in automobile combustion engines and lawn mowers.	This kind of engine is commonly used in small boats, motors, dirt bikes, go-karts, and chainsaws.

Applications of Four Stroke Engine

It is useful in a variety of applications. Some common applications are mentioned below:

1. Four-stroke engines are commonly found in engines that run on gasoline.
2. Four-stroke engines are found in cars, vans, and certain motorcycles.
3. It is also not uncommon for four-stroke engines to be used in small propeller aircraft, small motor-driven boats, and formula one cars.
4. These are the same engines seen in go-karts and lawnmowers.

Advantages of Four Stroke Engine

1. At low RPM, four-stroke engines produce more torque than two-stroke engines.
2. Engines with four strokes consume fuel only once every four strokes, which makes them more efficient.
3. Because power is created just once per four strokes and no oil or lubricant is added to the fuel, these engines emit less pollutants.

Disadvantages of Four Stroke Engine

1. These engine uses complex valve mechanisms that are operated and regulated by gears and chains.
2. A four-stroke engine contains many more parts than a two-stroke engine.

Wrapping It Up

That’s it. Thanks for reading. I hope I have covered everything. It would be helpful if you could let me know if there was anything I missed or if you have any doubts about anything I wrote.

Resources or External Links:

1. https://www.uti.edu/blog/motorcycle/how-4-stroke-engines-work
2. https://en.wikipedia.org/wiki/Otto_cycle

FAQs