Stroke (engine) facts for kids

A stroke in an engine is like one complete breath and action cycle. Imagine a machine that needs to do four main things to make power: suck in air and fuel, squeeze it, light it up, and then push out the used gas. When an engine does all these steps, it's called one "stroke." This is how many engines, especially four-stroke engines, work.

When an engine completes these steps – taking in fuel, squeezing it, burning it, and pushing out the exhaust – it makes the engine's main shaft spin. This spinning action is what powers cars, motorcycles, and many other machines. The engine keeps repeating these strokes very fast, and how fast it spins is measured in "RPMs," which stands for revolutions per minute.

What is a Four-Stroke Engine?

Most cars and many other vehicles use a type of engine called a four-stroke engine. This name comes from the fact that the engine needs four main movements or "strokes" to complete one full power cycle. Each stroke is a specific action that helps turn fuel into movement.

The Four Steps of a Stroke

Let's look at the four important steps that happen inside a four-stroke engine:

1. Intake Stroke

This is the first step, like the engine taking a deep breath. A valve opens, and the piston (a part that moves up and down inside the engine) moves down. This creates a space that sucks in a mix of air and fuel into the engine's cylinder. It's like pulling air into a syringe.

2. Compression Stroke

After the air and fuel are inside, the intake valve closes. Then, the piston moves back up, squeezing the air and fuel mixture into a very small space. Squishing the mixture makes it very hot and ready to burn with a lot of power. Think of it like pressing down on a bicycle pump.

3. Power Stroke (Combustion)

This is where the magic happens! Once the mixture is squeezed, a spark plug creates a tiny spark. This spark ignites the highly compressed air and fuel, causing a small explosion. This explosion pushes the piston down with great force. This powerful push is what makes the engine's shaft spin and creates the energy to move a vehicle.

4. Exhaust Stroke

After the power stroke, the used-up gases need to leave the engine. An exhaust valve opens, and the piston moves back up, pushing all the burnt gases out of the cylinder and into the exhaust pipe. This clears the way for the next intake stroke to begin the whole process again.

Revolutions Per Minute (RPMs)

RPMs, or revolutions per minute, tell you how many times the engine's main shaft spins in one minute. Each time the shaft spins, the engine has completed several "strokes." A higher RPM means the engine is working faster and producing more power. For example, when you press the gas pedal in a car, the engine's RPMs go up, meaning it's doing more strokes per minute to make the car go faster.

Images for kids

• 

  The phases/strokes of a four-stroke engine. 1: intake 2: compression 3: power 4: exhaust

See also

In Spanish: Carrera (motor) para niños