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Internal Combustion Engine: Lesson for Kids

Instructor: Shoshana Yarin

Shoshana has taught all grades with an emphasis in science and has a master's degree in science.

Have you ever wondered how a car engine works or thought maybe it was just too hard to understand? You can learn the basics of how an internal combustion engine works if you read this lesson.

Cars Run On Gas

How often do you ride in a car (or truck)? Well, hop on in because we're going for a ride!

Wait a minute! We need to put gasoline in the car before we go anywhere! Most cars have an internal combustion engine, which runs on gasoline. We're going to look at the four steps that create power in an engine, but first we'll talk about our fuel.

Gasoline is a liquid fuel that comes from processing oil. Engines were made to use gasoline because it is very combustible. That means it easily combusts, or burn by fire. Combustible materials can even explode!

Think of a burning candle. The wax burns (or combusts) and gives off energy in the form of heat and light. Gasoline gives off heat and light, too, but in a big bang sort of way. When gasoline combusts, it releases a LOT of energy. So much that it's enough to power a car!

Combustion of Gasoline
Combustion

The word 'internal' in 'internal combustion engine' means the combustion of gasoline takes place inside the engine. We don't see it happen. So let's look at the inside of an engine.

The Four-Part Cycle

There are lots of parts to a car but we're going to look at the four-part cycle that actually makes the car's power - enough for it to drive. Let's go through the steps of the four-part cycle of an internal combustion engine. As we go through, we'll be careful to call gasoline by its name. When we say 'gas,' we're talking about a state of matter like solids or liquids.

Step 1

A valve opens and closes to control a liquid or gas coming in. The 'intake valve' specifically lets in gasoline. Only a small amount of liquid gasoline comes through the valve.

Gasoline is very volatile which means it turns from the liquid state to the gas state very quickly. That's important because it must be in the gas state to combust. It also must have oxygen to combust, so the valve lets in air, too.

Valves in the Engine
Valves

Step 2

Inside is a piston, which is a cylinder-shaped object that moves up and down. The piston moves down to make room for the gas and air and then moves up to compress or smoosh the gases together and make the combustion bigger.

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