2‑Stroke vs 4‑Stroke Engines: Key Differences Explained

If you look around almost all mechanical devices are powered by either 2 stroke or 4 stroke engines. These two engines have an effective role in our daily life, from the transportation aspect to the small portable devices they powered. Though these engines are both internal combustion, their working principle is totally different. The existence of 2 strokes and 4 stroke engines are for specific reasons which are to power some types of applications. The term “stroke” is also called “cycle” hence 2 cycle and 4 cycle engines, having a great difference between them.

Today we’ll get to know the difference between 2-stroke and 4-stroke engines, their applications, working, and advantages and disadvantages.

The major difference between two-stroke and four-stroke engines is that it takes two strokes to completes a power cycle. That’s, the upward and downward movements of the piston are one revolution of the crankshaft. Whereas in four-stroke engines, it takes four strokes of the piston to complete a power cycle during two crankshaft revolutions.

In order words, the difference between two-stroke and four-stroke engines is how quickly the combustion cycle process occurs. in addition, it depends on the number of times the piston moves up and down during each cycle.

The terms “top dead center” (TDC) and “bottom dead center” (BDC) refers to the position of the piston within the cylinder. A stroke is completed when the piston moves from TDC to BDC or vice versa. A combustion cycle or combustion revolution is the complete process of gas and air being sucked into the piston, compressing, igniting, also releasing the exhaust.

Difference between two-stroke and four-stroke engines

Two-stroke engines

Two-stroke engines are often found in small applications such as hand-carried lawn and garden tools like string trimmers and chainsaws. All reciprocating internal combustion work through a five circle such as intake, compression, ignition, combustion, and exhaust. These five cycles are completed in two strokes of the piston in two-stroke engines which is one revolution of the crankshaft.

In 2 stroke engines, the compression stroke and combustion stroke of the compressed fuel occur simultaneously. Also, the intake and exhaust stroke takes place at the same time as the exhaust gas escape and a fresh fuel mixture enters the cylinder.

Because the power is produced once every 2 strokes of the piston, the spark plug fire once in every single revolution. Finally, the system requires oil to be pre-mixed with the fuel.

Advantages and disadvantages of two-stroke engines

Advantages:

• Designed for smaller applications
• Higher power to weight ratio compared to four-stroke engines
• Two-stroke engines are lighter.
• 2 stroke engines rev up to higher speeds compare to 4 stroke engines
• Small 2 stroke engines use intake and exhaust ports instead of valves, thus saving the weight and cost of a valve train.
• 2 stroke engines have simpler designs and can be easily fixed.
• 2 stroke engines are more powerful compare to 4.

Disadvantages:

• The engine is significantly louder and has a distinctive, high-pitched “buzzing” sound
• Wear tend to occur faster because it runs at a higher rpm.
• It’s not environmentally friendly as the premixed oil is released as exhaust.

Watch the video below to learn the working of two-stroke engines:

Four-stroke engines

Four-stroke engines are used in commercial cars, buses, trucks, etc. its piston completes 2 strokes during each revolution. The spark plug fire once in every other revolution and power is produced in every 4 strokes of the piston. Pre-mixing of oil and fuel is not needed in this system like the 2 strokes, it’s designed with a separate compartment for oil.

Advantages and disadvantages of four-stroke engines

Advantages:

• High efficiency because fuel is consumed once in every four strokes.
• Four-stroke engines are quiet and create a smooth sound
• Four-stroke engines are generally more durable compare to two strokes
• A four-stroke engine is environmentally friendly compare to two strokes

Disadvantages:

• Four-stroke engines are heavier, weigh about 50% more compare to two.
• It creates higher torque at a lower rpm
• The system has more parts which could cause a breakdown.
• It’s expensive and repairs cost more.

Watch the video below to learn the working of four-stroke engines:

Now let look at the difference between two-stroke and four-stroke engines in tabular form:

Difference between two 2 stroke and 4 stroke engines
s/n	2 stroke engines	4 stroke engines
1	Used in lighter applications	Used in heavier applications
2	High efficiency	Working efficiency is moderate
3.	More torque at a higher rpm is created	Higher torque at lower rpm is created
4.	The engine is louder and creates some buzzing sound	It’s quiet and makes a cool sound.
5.	The engine is more powerful	Its working is moderate
6.	It wears out faster	Engine is durable

In conclusion, knowing the difference between 2-stroke and 4-stroke engines is essential as an auto user. This is because they are common in applications to use in our daily life. I have covered the difference between two-stroke and four-stroke engines, their applications, working, advantages and disadvantages.

I hope you enjoyed reading the article, if so, kindly share it with other students. Thanks for reading, see you next time!