A four-stroke cycle engine is an internal combustion engine that uses four piston strokes to complete one full combustion cycle. It is the most common type of internal combustion engine and is typically found in petrol vehicles.
If you are curious about the workings of a four-stroke cycle engine and its pros and cons, dive into this detailed overview.
Parts of a Four-Stroke Cycle Engine
All parts required of a four-stroke cycle engine are as follows.
Piston
The four-stroke cycle engine heavily depends on the back-and-forth movement of the piston. This back-and-forth movement, also known as piston strokes, produces power in the engine and initiates combustion. Four distinct piston strokes in the cylinder complete one four-stroke cycle. The piston rings close the gap between the cylinder and the piston to ensure efficient combustion.
Crankshaft
The crankshaft is a vital component of the four-stroke engine as it connects the output section of the engine to the input section. It converts the reciprocal motion (up-and-down movement) of the piston into rotational motion and delivers it to the gearbox.
Connecting Rod
The connecting rod of the engine works as a lever arm and transfers force from the piston to the crankshaft. As the piston moves upwards and downwards during the compression and power stroke, the connecting rod experiences compression and tension respectively.
Flywheel
It is a device that stores rotational energy in the engine. The car engine flywheel also plays a major role in engine starting and smoothing out the rotation speed of the crankshaft. This ensures a smooth engine operation.
Inlet and Outlet Valves
The inlet and outlet engine valves are responsible for controlling the airflow in a four-stroke engine. The inlet valve allows air to enter before combustion and the outlet valve allows the air-fuel mixture to exit the cylinder.
Spark Plug
Spark plugs are an essential part of the combustion chamber responsible for delivering electric current to the chamber. This ignites the air-fuel mixture, resulting in sudden gas expansion. The spark plug also emits an electricity spark and creates the ignition required to start a vehicle.
How Does a Four-Stroke Engine Work?
A four-stroke cycle engine works in four different stages. Each stage is dependent on the movement of the piston in the cylinder. One complete operating cycle requires an intake stroke, a compression stroke, a power stroke and an exhaust smoke. One complete cycle allows the crankshaft to rotate 720 degrees and complete two full revolutions.
Here is a detailed process of the four-stroke cycle of an engine.
Intake Stroke
In the intake stroke, the air-fuel mixture enters the combustion chamber. The piston moves from the top dead centre (TDC) to the bottom dead centre (BDC) of the cylinder. This creates a low pressure in the cylinder. The intake valve then opens, forcing the air-fuel mixture through the intake valve into the cylinder. This first movement of the piston rotates the crankshaft to 180 degrees. The intake valve then closes, trapping the air-fuel mixture in the cylinder.
Compression Stroke
As the name suggests, the trapped air is compressed in the cylinder in this stage. The piston moves from the bottom to the top of the cylinder, compressing the trapped air-fuel mixture and allowing more energy to be released. The crankshaft rotates 180 degrees to complete one revolution. Both the valves remain closed in this stage, ensuring that the cylinder is sealed before the charge is formed.
The charge refers to the volume of air-fuel mixture within the combustion chamber. When the air-fuel mixture is compressed, it allows a higher energy release once the charge is ignited. The flywheel maintains the momentum required to reduce the charge from a large volume to a smaller volume.
Compressing the charge causes an increase in the compressing force, allowing heat to be generated. This causes the charge temperature to rise and leads to an increase in fuel vaporisation. High temperatures in the chamber aid in faster combustion after ignition. Once the high-temperature charge in the chamber is ignited and oxidised through the combustion process, heat energy is released which is then used to power the vehicle.
Power/Combustion Stroke
This is the stage where the combustion is completed. The hot expanding gases in the cylinder push the piston back to the bottom of the cylinder. This movement transfers force to the crankshaft through the connecting rod. The force applies torque to the crankshaft, as a result, crankshaft rotation is initiated. The crankshaft rotates another 180 degrees to complete this stroke. The torque produced depends on three factors, the pressure on the piston, the size of the piston and the throw of the engine. Both the valves remain closed during this stage.
Exhaust Stroke
One complete operation cycle concludes with the exhaust stroke. The exhaust stroke occurs when the cylinder is filled with hot expanding gases. The inertia of the flywheel pushes the piston back to the top dead centre. The exhaust valve then opens and the piston pushes the exhaust gases out of the valve. At this point, the piston is at the top dead centre, moving the crankshaft 180 degrees further, completing the 720-degree cycle. The piston is then ready to start a second cycle by repeating the process.
Advantages of a Four-Stroke Cycle Engine
Some advantages of a four-stroke engine include:
- Yields higher torque levels at lower RPM.
- It is fuel efficient as it consumes fuel every four strokes.
- Four-stroke engines are better for the environment as compared to two-stroke engines as they do not require lubricant or oil mixed in the fuel.
- These engines last longer as they are durable.
Disadvantages of a Four-Stroke Cycle Engine
Some disadvantages of the four-stroke engine include:
- More weight as compared to other engines due to additional components.
- Require regular maintenance.
- Generates less power as compared to a two-stroke engine.
- Higher costs for repairs and maintenance due to an increased number of components and a complex layout.
FAQs
What is the Working Principle of a Four-Stroke Engine?
A four-stroke cycle engine uses the back-and-forth movement of the piston to initiate combustion. Four piston strokes (intake, compression, power and exhaust) in the cylinder complete one operating cycle.
What is a Four-Stroke Engine?
An internal combustion engine that utilises two complete passes of the piston in the cylinder is called a four-stroke engine.
What are the Applications of a Four-Stroke Engine?
The four-stroke engine is the most common type of small engine typically used in various gasoline vehicles such as cars, trucks and some bikes.
This was all about four-stroke cycle engines and how they work. Four-stroke engines last longer as they can withstand higher amounts of wear and tear and are also fuel-efficient.
If you wish to get a car with a four-stroke cycle engine, browse through new cars for sale in the UAE and choose the vehicle of your choice.
Stay tuned to UAE’s leading auto blog to learn more about different car engines and their working mechanisms.
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