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How Does a Piston Engine Work?

Boldmethod

Whether you're brushing up on the basics before your next flight review, or you're just starting out, knowing how your engine turns your prop is a must-know.

Looking for how a jet engine works? We have an article for that too.

The Components

We'll keep the components simple since there is some variation between engines, but the principles will stay the same.

The Four Strokes

You know the players, now it's time to learn the game. Your engine's operation can be broken down into 4 simple steps.

  • Intake
  • Compression
  • Power
  • Exhaust

Intake

Your engine mixes fuel and air in the intake manifold. As it mixes, the intake valve opens as your piston moves down, drawing the fuel-air mixture into the combustion chamber.

Compression

As the name suggests, the piston is forced up after the intake valve closes, compressing the fuel-air mixture before it is ignited.

Power

This is the only step that actually provides you with horsepower. Everything else is simply about getting everything in the right place, at the right time.

Right before the piston reaches it's highest point (top-dead-center), your spark plugs send a current arching across their prongs, igniting the fuel-air mixture. Different engines have different designs, so their exact firing point will vary depending on your engine's model. As the fuel and air combust they expand, pushing down the piston. The directional motion of the piston moving down is converted to rotational motion as your piston turns the crankshaft, providing power.

Exhaust

Now that your engine has extracted the potential energy from the fuel-air mixture you sucked into the cylinders, it's time to set it up again. Your exhaust valve opens, and the piston moves up, pushing the exhaust gas out of the cylinder and into the exhaust system.

Now that you've explored all the strokes individually, you can piece them together in the animation below.

Ignition

How do your spark plugs get their current? Connected to your engine are (generally) two magnetos. Magnetos are permanent magnets that can generate a current when spun close to a coil of wire (electromagnetic induction). This current then flows to your sparkplugs to ignite the fuel-air mixture.

But how are your Mags powered? For increased redundancy your aircraft's ignition system isn't tied to your battery, so your mags use the rotational motion generated by your engine to spin them. Meaning, if you turned off or lost your battery or alternator power in flight, your engine would keep working.

Want more power?

Some engines have a turbocharger or a supercharger to get more out of your intake stroke.

Nicolas Shelton

Nicolas is a commercial pilot from Southern California. He is currently studying at Purdue University, where he is working on advanced pilot ratings. You can reach him at nicolas@boldmethod.com.

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