What Are the Differences Between a 2-Stroke and a 4-Stroke Engine

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The motor internal combustion engine is divided into two categories: two-stroke and a four-stroke engine. These two categories dominate the styles of internal combustions engines. Both of them are powered by gas, but they have vast differences.

The motor engines have different efficiency, cycles, development curves and many more. In this article, we will compare the two types of engine in-depth.  You might have a question what’s the main difference between them?

So, Let’s find out…

2-Stroke and vs 4-Stroke Engine

Intake

A four-stroke engine completes four distinct cycles in one thermodynamic cycle. The stroke of the piston starts at the center. The valve comes down from the top side of the cylinder to the bottom. In this process, it increases the volume of the barrel.

A combination of air and fuel is forced by maximum atmospheric pressure into the cylinder via the intake port.

A two-stroke engine completes two different cycles in a single thermodynamic cycle. The mixture air and fuel is drawn into the crankcase that is developed during the upstroke of the cylinder by the vacuum.

Compression

In a four-stroke engine, compression occurs when intake and exhaust valves are closed. The piston returns to the top part of the cylinder. This process will then compress fuel or air combination into the head of the barrel.

During the downstroke in 2-stroke engine, the valve is closed due to atmospheric pressure. The mixture will be compressed in the crankcase; the piston will rise and drive the wheel momentum and compressed the combination of air and fuel. Another stroke happens beneath the cylinder at the same time.

Power

Power is the start of the 2nd revolution of the four cycles in four-stroke engine. The cycle occurs when the piston is close to TDC (Top Dead Centre). The spark plug will ignite gasoline engine due to a mixture of compressed of air and fuel. The ignition will also occur due to compression of a diesel engine. The outcome of the pressure from the combustion of the compressed fuel and air will force the piston back down to BDC (Bottom Dead Centre)

The spark plugs will ignite the air/fuel mixture at top dead center. The burnt fuel will expand and force the piston downwards. This process will compete for the second cycle. Another compression will continue to work beneath the stroke at the same time.

Exhaust

During Exhaust, the piston will again return to the top dead center. It occurs when the exhaust valve is open. The pressure will expel the mixture of air and fuel via the exhaust valve.

At the end of the stroke in two-stroke engine, the piston will open the intake valve and force the compressed fuel/air mixture to expel into the main cylinder. It will expel gases out of the exhaust valve usually found at the opposite of the barrel.

Comparison

Power

In a two-stroke engine, every cycle of the stroke is the power stroke. In four-stroke engine, power is delivered in one revolution only. This scenario offers a two-stroke engine a significant boost in power. Due to sufficient force, the acceleration will be high, and delivery of energy will be uniform.

Winner: 2-stroke engine

Torque

Overall, the 4-stroke engine makes additional stroke than a 2-stroke engine at low revolution power minute.  At high acceleration, the two-stroke engine gives high torque.

Draw

Fuel efficiency

The 4-stroke engine has the highest fuel efficiency because it consumes fuel only in one revolution every four strokes. In a 2-stroke engine, fuel is utilized in the entire alternate stroke. This reason makes the engine less fuel efficient.

Winner- 4-stroke engine

Construction and design

The 2-stroke engine does not have valves. It has an inlet and outlet port making its construction simple. 4- Stroke engine has complicated valves and mechanisms. It is operation by complex chain and gears. They are many parts which make it difficult to troubleshoot.

Winner- 2-stroke engine

Durability

As the engine runs fast, it tends to wear out. The 2-stroke engine is designed to have a high revolution per minute. For instance, an engine that can run for 10000RPM, the engine parts will wear out quickly. A 4-stroke engine with 100RPM lasts longer than a 2 –stroke engine.

Winner- 4-stroke engine

Pollution

For a 4-stroke engine power is generated once in every four strokes. There is also no oil or lubricants that are added hence environmental friendly due to less pollution. 2- Stroke engine produces more pollution due to combustion of fuel. A lot of smoke is developed and lead to dangerous pollutants.

Winner- 4-stroke

Cost

A 4-stroke engine has many parts than a 2-stroke engine. The engine of a 4-stroke requires repair and maintenance regularly hence many expenses.

Winner: 2-stroke engine

Fuel consumption and wastage

In a 4-stroke engine, only the moving parts need lubrication. There is no lubricant or oil is added to the fuel.

In a 2-stroke engine, fuel is added to replace gas that has undergone combustion and expelled as exhaust gases. This process results in significant wastage of fuel.

Additionally, there is incorrect combustion because many gases are trapped in the combustion chamber. Maximum power will not be delivered due to incomplete combustion of gases.

Winner – 4 stroke engine

The main points of the 4-stroke engine include:

  • High torque
  • Greatest fuel efficiency
  • Environmental friendly
  • Durable
  • Less wastage of fuel
  • Complicated design and construction
  • Expensive
  • Less powerful

While 2-stroke engine:

  • Simple installation and design
  • More powerful
  • Less fuel efficient
  • More pollution
  • High wastage of fuel
  • Incomplete combustion of fuel

Based on difference functionalities the winner goes to the 4-stroke engine due to performance. Many moving parts means that it can be improved using the latest technology, unlike 2-stroke engine.

Frequently Asked Questions (FAQs)

Is a 2-stroke engine potent than the 4-stroke engine?

A two-stroke engine is more powerful than 4-stroke engine because it produces power twice amount generated by the 4-stroke engine at the same size. 2-stroke engine ignites energy in each revolution while four-stroke engine fires once in all the four-revolutions. However, noise produced by the 2-stroke engine is equivalent to its power produced.

Are 2-stroke engines better than the four-stroke engines?

The two-stroke engine is an unusual type of engine that does not live as long a 4-stroke engine exists. It has no consistent lubrication and wear-out fast due to high acceleration. It needs a mixture of gas and oil to lubricate moving parts that connect cylinder walls and connecting rod.

Which one is faster between 2-stroke and 4-stroke engine?

Manufacturers design 2-stroke engine to accelerate faster than a 4-stroke engine. 2-stroke has two cycles; each cycle is doing many things than 4-stroke which has four periods and each cycle doing one task.

Final Thoughts

From the above information, both internal combustion engines have inherent advantages and disadvantages. You should select either 4-stroke or 2-stroke depending on a given work.

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