Four Strokes to Go: How a Car Engine Actually Fires
Right now, if a car engine is running nearby, tiny explosions are happening inside it, thousands of them every single minute! Each explosion pushes a metal piston, and that push is what eventually spins the wheels. This whole process repeats in a pattern called the four-stroke cycle, and once you learn the four steps, you'll never look at a car the same way again.
What You'll Learn
- The name and job of each of the four strokes - What a piston and cylinder actually do - Why the process is called combustion - How this cycle repeats to keep a car moving
Stroke 1: Intake
Inside the engine is a hollow tube called a cylinder, and inside that tube is a piston, a solid metal plug that slides up and down. In the intake stroke, the piston slides DOWN, and as it does, a valve opens to let in a mix of fuel (gasoline) and air. Think of it like pulling back a syringe to suck in liquid.
Stroke 2: Compression
Next, the valve closes and the piston slides back UP, squeezing that fuel-air mixture into a much smaller space. Squeezing gas into a tighter space is called compression, and it makes the mixture much easier to ignite, like packing a snowball tightly before you throw it.
At the top of compression, a spark plug fires a tiny electric spark, hotter than lightning for a split second, and ignites the compressed fuel-air mixture. This is the moment of combustion, a small controlled explosion that happens dozens of times per second while an engine runs.
Stroke 3: Power
That explosion from combustion pushes the piston back DOWN with tremendous force, this is the power stroke, the only one of the four strokes that actually generates power. This downward push is transferred through a rod to the crankshaft, a rotating metal shaft that turns that up-and-down motion into the spinning motion that eventually reaches the wheels.
Stroke 4: Exhaust
Finally, a different valve opens and the piston slides back UP one more time, pushing the leftover burned gas out of the cylinder and out the tailpipe as exhaust. Then the whole cycle starts over again with intake. A typical car engine repeats this full four-stroke cycle thousands of times every minute while driving.
Match each stroke to what happens during it.
Terms
Definitions
Drag terms onto their definitions, or click a term then click a definition to match.
Which stroke is the only one that actually generates power to move the car?
Why does the engine compress the fuel-air mixture before igniting it?
Build a Four-Stroke Flip Book
Draw four simple diagrams, one per index card or paper square: Intake, Compression, Power, and Exhaust. In each drawing, show the piston position (up or down), whether a valve is open, and label what is happening to the fuel or gas. Staple the cards together in order and flip through them to show the full cycle repeating.
Flashcards — click each card to reveal the answer
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