What is a Four-stroke Engine in Cars and What are Its Parts?

Four-stroke engines power a wide range of applications, including cars and motorcycles. Also called Otto cycle or four-cycle engines, these form the principle on which most modern automobile engines function.

In this comprehensive guide, we’ll dive deep into the definition of a four-stroke engine, its functionalities, and the major difference between 2-stroke and 4-stroke engines.

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What is a Four-stroke Engine in Cars?

It is a widely used type of internal combustion engine in today's market. It works through four piston strokes, namely power, compression, intake, and exhaust, that complete a full operating cycle.

All these strokes work together in a defined sequence to convert fuel into mechanical energy. This helps power various applications like automobiles, and motorcycles, to name a few, that typically run on gasoline or diesel fuel.

What are the Different Parts of a Four-stroke Engine?

There are 6 different parts of a 4-stroke engine.

Piston: The role of the piston is to move up and down inside the cylinder, converting gas forces to the crankshaft’s mechanical rotation.
Crankshaft: This part of a four-stroke engine converts the piston's up and down motion into smooth motion.
Connecting Rod: The connecting rod acts as a lever arm, linking the piston to the crankshaft.
Flywheel: A flywheel stores energy and helps maintain optimal engine momentum.
Inlet and Exhaust Valves: These control fresh air flow in an air-fuel mixture out of the cylinder.
Spark Plug: This ignition device generates an electric spark to ignite the fuel-air mixture during the power stroke.

What are the Phases a Piston Undergoes in a Four-stroke Engine?

4-stroke engines have 4 valves through which the piston goes through to complete on full cycle. Let’s discuss each phase in detail.

1. Intake Stroke

The intake stroke, which is the first step of the four-stroke engine cycle, takes place when the fuel-air mixture enters the combustion chamber inside the cylinder.
The piston then moves from the top dead centre (TDC) to the bottom dead centre(BDC).
The inlet valve remains open a few degrees after BDC, and the exhaust valve is shut.
Later, the inlet valve closes, sealing the air-fuel mixture in the cylinder.

2. Compression Stroke

During the compression stroke, there is a movement of the piston from BDC to TDC in the cylinder.
The outlet and inlet valves are closed to ensure the cylinder is sealed. This results in compression.
The piston’s upward motion compresses the air-fuel mixture in the combustion chamber.

3. Power Stroke

It happens before the compressed fuel-air mixture ignites.
The ignition and combustion forces the piston to move downwards from TDC to BDC, thus generating the power that allows the vehicle to move forward.
Both the inlet and outlet valves remain closed.

4. Exhaust Stroke

Occurs after the BDC receives the piston in the power stroke.
The combustion process here is complete, filling the cylinder with exhaust gases.
The valves of the exhaust open, permitting the gases to exit.
Additionally, the piston is pushed back to TDC via the inertia of the flywheel, which also marks the completion of one operating cycle.

What is the Difference Between a 2-stroke Engine and a 4-stroke Engine?

Here is a table highlighting the major difference between the 2 engine types. Choosing the right entirely depends upon your specific requirements.

Point of Comparison	2-stroke Engine	4-stroke Engine
Weight	Light in weight	Approximately 50% heavier than a 2-stroke engine
Efficiency	Consume fuel every 2 strokes, leading to more fuel wastage	Consumes fuel once every 4 strokes and hence more efficient
Torque	There is a higher RPM and more torque	Creates higher torque at a lower RPM, thus providing efficient low-end power
Noise	Generates loud noise	Owing to smooth operation, 4-stroke engines are quieter compared to 2-stroke
Repair Cost	Easier and less expensive to repair owing to simple construction	Higher repair costs because of complex designs and other components
Application	Commonly found in smaller applications like boat motors and chainsaws	Commonly found in larger applications like go-karts and internal combustion engines in cars

The importance of four-stroke engines in today’s automobile world is owing to its ability to provide reliable and efficient power solutions while addressing environmental concerns through better fuel efficiency.

FAQ's about Four Stroke Engine in Cars

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What are the benefits of a four-stroke engine?

Four-stroke engines offer various advantages, namely enhanced fuel efficiency, smoother operation of the vehicle, and lower gas emissions, to name a few.

Why are “four-stroke engines” named so?

Four-stroke engines are named so as it completes one full operating cycle using four distinct strokes of the piston - intake, compression, power, and exhaust stroke.

What makes four-stroke engines more efficient than 2-stroke engines?

A four-stroke engine is more efficient than a two-stroke engine owing to factors like the availability of separate strokes in each phase and a dedicated lubrication system ensuring the engine's longevity.