What is four-stroke engines, its Stroke Cycle, Diagram, Working, and Benefits

Summary 

Four-stroke engines are internal combustion engines used in automobiles, like trucks, cars, and some modern motorbikes (most motorbikes work with a two-stroke engine). Four-stroke is referred to as the combustion cycle.

A four-stroke, also called a four-cycle engine, is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder in either direction.

The combustion cycle of a four-stroke engine is intake/inlet stroke, compression stroke, power stroke, and exhaust stroke. These stages all work together to propel the vehicle.

The major parts of a four-stroke petrol engines are the piston, crankshaft, connecting rod, flywheel, inlet and outlet valves, and spark plug.

Four-stroke petrol engines are the most common internal combustion engine design for motorized land transport, being used in automobiles, trucks, diesel trains, light aircraft, and motorcycles. The major alternative design is the two-stroke cycle.

The four-stroke cycle was originated by French engineer Alphonse Beau de Rochas in 1862. The four-stroke cycle is often called the Otto cycle, after the German engineer Nikolaus August Otto, who designed an engine on that principle in 1876. Learn the difference between four-stroke and two-stroke engines here!

Difference between 2 stroke and 4 stroke engines

Now, let’s go deep to explain what four-stroke engines are, their stroke cycle, diagram working, and benefits!

What is four-stroke engines?

A four-stroke cycle engine is an internal combustion engine that uses four different piston strokes such as intake, compression, power, and exhaust to complete one operating cycle. A stroke refers to the full travel of the piston along the cylinder, in either direction.

The piston make two complete passes in the cylinder to complete one operating cycle. An operating cycle requires two revolutions (720°) of the crankshaft.

This means that the crankshaft must go around twice, and each piston moves up and down two times, to produce one pulse of power. In another word, the piston goes up-down, up-down, for each firing of the spark plug for petrol engines.

Four-stroke engines are common internal combustion engine mostly used for land transportation such as automobiles, trucks, diesel trains, and motorcycles and it doesn’t matter if they burn petrol or diesel.

The four-stroke cycle is often called the Otto cycle, after the German engineer Nikolaus August Otto, who designed an engine on that principle in 1876.

The Four-Stroke Cycle

Intake/Inlet Stroke.

This is the first stroke cycle, also known as induction or suction stage. The stroke of the piston begins from the Top Dead Center (T.D.C.) and ends at the Bottom Dead Center (B.D.C.).

During this stroke, the intake valve is opened so that the piston can introduce the air-fuel mixture into the cylinder through a partial vacuum (negative pressure). This occurs during the downward movement of the piston.

Compression Stroke.

At this stage, the intake valve is closed, blocking the air-fuel mixture from escaping. The compression stroke begins at B.D.C, or just at the end of the suction stroke, and ends at T.D.C.

In this stroke, the piston compresses the air-fuel mixture in preparation for ignition during the power stroke. Both the intake and exhaust valves are closed during this stage.

At the end of the stroke, the availability of a spark plug allows the ignition of the air-fuel mixture, providing the energy required for combustion.

Combustion Stroke.

This stage is also known as the power or ignition stroke. It is the start of the second revolution of the four stroke cycle. The crankshaft is said to have completed a full 360 degree revolution at this point.

For gasoline engines, the compressed air-fuel mixture is ignited by a spark plug. While diesel engines is achieved by the heat generated by high compression. The piston is forcefully returned to the B.D.C which produces mechanical work from the engine to turn the crankshaft.

Exhaust Stroke.

This is the final stage of the combustion cycle, also known as outlet. It occurs when the piston moves back downward, and the exhaust valve opens. As the valve opens, the exhaust gas is pushed out by the piston when it moves back upwards.

In other words, the piston once again returns from B.D.C. to T.D.C. while the outlet valve is open. This action expels the spent air-fuel mixture through the exhaust port.

 

Diagram of four-stroke Cycle

 

Working

The thermal efficiency of an engine is the ability to convert the fuel (chemical energy) to mechanical energy. This energy will vary due to the design and model of the vehicle.

Typically, four-stroke petrol engines are opportune to convert 20% of fuel (chemical energy) to mechanical energy. 15% of it is used to move the wheels, and 5% is lost to its mechanical elements and friction. 

However, the engine can be improved through thermodynamic efficiency through a higher compression ratio. The ratio is determined between the maximum and minimum volume of the engine chamber.

An engine with a higher ratio will allow the fuel-air mixture to be immense, which will produce higher pressure, make the housing hotter, and increase thermal efficiency. Watch this video below to learn more on the working of four-stroke engines:

 

Benefits of Four-Stroke Engines

The four-stroke engine, a mainstay in automotive engineering, offers numerous benefits that make it the engine of choice for most gasoline-powered vehicles. Here are some key advantages:

1. Efficiency: The four-stroke engine is highly efficient due to its distinct intake, compression, power, and exhaust strokes. This cycle maximizes fuel combustion and energy production, leading to better fuel economy.
2. Power: Known for its robust power output, the four-stroke engine delivers smooth and consistent power throughout its operation. This makes it suitable for a wide range of vehicles, from compact cars to heavy-duty trucks.
3. Durability: With fewer moving parts and a design that reduces wear and tear, four-stroke engines are renowned for their durability. Regular maintenance can keep these engines running smoothly for many years, offering a long lifespan.
4. Reduced Emissions: Four-stroke engines are generally more environmentally friendly than their two-stroke counterparts. They produce fewer emissions due to more complete combustion of fuel, contributing to lower pollution levels.
5. Maintenance: While four-stroke engines require more complex maintenance than two-stroke engines, their design allows for easier diagnosis and repair of issues. This ensures that any necessary repairs can be handled efficiently, keeping downtime to a minimum.
6. Versatility: The versatility of the four-stroke engine allows it to be used in various applications, including cars, motorcycles, boats, and lawn equipment. Its adaptability is a testament to its superior design and functionality.

Bottom Line

The four-stroke engine stands as a cornerstone of modern automotive engineering, delivering a balance of power, efficiency, and reliability. Its cycle of intake, compression, power, and exhaust ensures optimal performance, making it a preferred choice for most gasoline-powered vehicles.

Understanding the intricacies of the four-stroke engine not only highlights in its design but also the importance of regular maintenance to keep your engine running smoothly.

Whether you’re a car enthusiast or a casual driver, appreciating the four-stroke engine’s role in your vehicle can enhance your driving experience and prolong your engine’s lifespan.

By familiarizing yourself with the Workings and maintenance of a four-stroke engine, you contribute to its longevity and efficiency, ensuring a smoother and more reliable ride.

That is all for this article, where I explained what four-stroke engines are, their stroke cycle, diagram working, and benefits. I hope it was helpful, if so, kindly share with others. Thanks for reading, see you around!