How Does A Small Engine Work? 2 & 4 Cycle

Summary

This video script provides an educational overview of small engine mechanics, focusing on the differences between two-stroke and four-stroke engines. It explains the four-stroke cycle, which includes intake, compression, power, and exhaust, using a lawnmower engine as an example. The script also touches on the two-stroke engine, which combines the intake and compression strokes and uses a mixture of oil and gas for lubrication. The presenter humorously introduces 'four-mix' engines, which are four-stroke engines that require oil mixed with gas, and encourages viewers to subscribe and engage with the content for more insights.

Takeaways

• 🔧 The script explains the workings of small engines, specifically focusing on four-stroke and two-stroke engines.
• 🌀 A four-stroke engine completes one cycle through four distinct strokes: intake, compression, power, and exhaust.
• 💧 In a four-stroke engine, the intake stroke involves drawing a fuel-air mixture into the combustion chamber as the piston moves downward.
• 🔥 The compression stroke sees the piston compressing the fuel-air mixture in the combustion chamber, preparing it for ignition.
• ⚙️ The power stroke occurs when the spark plug ignites the compressed fuel-air mixture, causing an explosion that drives the piston downward.
• 🌬️ The exhaust stroke expels the burnt gases from the combustion chamber as the piston moves upward and the exhaust valve opens.
• 🛠️ A key difference between four-stroke and two-stroke engines is the presence of a crankcase for engine oil in four-stroke engines, versus a combined oil-gas mixture in two-stroke engines.
• 🚫 Two-stroke engines do not have a separate crankcase for engine oil; instead, oil is mixed with the fuel for lubrication.
• 🔄 The script humorously suggests that small engines 'run on magic,' highlighting the complexity of their operation.
• 🛑 The script also touches on 'four-mix' engines, which are four-stroke engines that require oil mixed with the fuel, similar to two-stroke engines.
• 👨‍🏫 The educational nature of the script is intended to clarify the differences between engine types and their operational cycles.

Q & A

What is the difference between a four-stroke and a two-stroke engine?

A four-stroke engine completes one cycle through four separate strokes: intake, compression, power, and exhaust. It has a separate crankcase for engine oil. A two-stroke engine completes its cycle in only two strokes: the intake and compression occur simultaneously, followed by combustion and exhaust in the second stroke. It mixes oil with the fuel for lubrication, as it doesn't have a separate crankcase for engine oil.

What are the four strokes of a four-stroke engine?

The four strokes of a four-stroke engine are intake, compression, power, and exhaust. During the intake stroke, the air-fuel mixture is drawn into the combustion chamber. The compression stroke compresses the mixture, the power stroke ignites the mixture causing the piston to move, and the exhaust stroke expels the burnt gases.

How does the carburetor play a role in the intake stroke of a four-stroke engine?

The carburetor mixes air and fuel before the intake stroke. As the piston moves downward, it draws air across the carburetor, pulling fuel from the float bowl through the center nozzle. The air and fuel mix is then carried into the combustion chamber through the intake manifold as the intake valve opens.

What is the purpose of the compression release on some engines?

The compression release is used to relieve some of the compression in the engine to make it easier to start. It works by momentarily bumping the valve open during the compression stroke, reducing the pressure. When the engine is running, centrifugal force keeps the compression release disengaged to prevent continuous bumping.

How does the spark plug contribute to the power stroke in a four-stroke engine?

The spark plug ignites the compressed air-fuel mixture in the combustion chamber during the power stroke. This ignition causes a small explosion that pushes the piston downward, providing power to the engine.

What is the role of the exhaust valve in the exhaust stroke of a four-stroke engine?

The exhaust valve opens during the exhaust stroke to expel the burnt gases from the combustion chamber. The piston moves upward, pushing the exhaust gases out through the open exhaust valve.

Why is it necessary to mix oil with gasoline in a two-stroke engine?

In a two-stroke engine, oil is mixed with gasoline to provide lubrication since there is no separate crankcase for engine oil. Without oil mixed in the fuel, the engine would lack lubrication and could be damaged.

What are the two strokes of a two-stroke engine?

The two strokes of a two-stroke engine are the intake and compression stroke followed by the combustion and exhaust stroke. The air-fuel mixture is drawn in and compressed in the first stroke, and then ignited and expelled in the second stroke.

What is a four-mix engine and how does it differ from a typical four-stroke engine?

A four-mix engine is a four-stroke engine that does not have a separate crankcase for engine oil. Instead, it requires oil to be mixed with the gasoline, similar to a two-stroke engine, for lubrication.

What are some variations in how two-stroke engines deliver the air-fuel mix to the combustion chamber?

Two-stroke engines can use a reed valve or piston porting to deliver the air-fuel mix to the combustion chamber. Some engines may also have a wedge on the piston to help deflect exhaust gases out during the exhaust stroke.