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 lives, from the transportation aspect to the small portable devices they power. 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, have 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.
Contents
The major difference between two-stroke and four-stroke engines is that it takes two strokes to complete a power cycle. That is, 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) refer 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.
Check out: Understanding two-stroke diesel and gasoline engines
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 works through five circles 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 fires 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 compared 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 compared to 4.
Disadvantages:
- The engine is significantly louder and has a distinctive, high-pitched “buzzing” sound
- Wear tends to occur faster because it runs at a higher rpm.
- It’s not environmentally friendly as the premixed oil is released as exhaust.
Check out: Applications, Pros, and Cons of Two-Stroke Engines
Watch the video below to learn the workings 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 fires 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-stroke
- A four-stroke engine is environmentally friendly compared to a strokes
Disadvantages:
- Four-stroke engines are heavier and weigh about 50% more compared 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.
Check out: Diesel engines and gasoline engines: Detailed explanation
Watch the video below to learn the workings of four-stroke engines:
Now let’s 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 |
Related Article:
- Applications, Pros and Cons of Two-Stroke Engines
- Understanding four-stroke engines
- Understanding two-stroke diesel and gasoline engines
- Difference between SI (Spark ignition) and CI (Compression ignition) engines
- Understanding the basic parts of a car engine
Conclusion
In conclusion, knowing the difference between 2-stroke and 4-stroke engines is essential for an auto user. This is because they are common applications to use in our daily lives. 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!
