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Whether you’re polishing up the basics before your next flight review or just embarking on your aviation adventure, knowing how your engine turns that propeller is a crucial piece of knowledge.
The Components
We’ll keep the components straightforward as there can be some variations among engines, but the principles remain the same.
The Four Strokes
Your engine’s operation can be broken down into four simple steps.
- Intake
- Compression
- Power
- Exhaust
Intake
In the intake manifold, your engine mixes fuel and air. As the intake valve opens while the piston descends, it draws in the fuel-air mixture into the combustion chamber.
Compression
As the name suggests, after the intake valve shuts, the piston is forced upward, compressing the fuel-air mixture before ignition.
Power
This is the only step that actually generates horsepower. Everything else is about getting everything in the right place at the right time.
Just before the piston reaches its highest point (top-dead-center), your spark plugs send a spark across their prongs, igniting the fuel-air mixture. Different engines have different designs, so the exact firing point varies depending on your engine model. As the fuel and air combust and expand, it pushes down the piston. The directional motion of the piston descending is converted into rotational motion as the 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. The exhaust valve opens, and the piston rises, pushing the exhaust gas out of the cylinder and into the exhaust system.
Now that you’ve explored each stroke individually, you can piece them together in the animation below.
Ignition
How do your spark plugs get their spark? Connected to your engine are (generally) two magnetos. Magnetos are permanent magnets that can generate a current when spun near 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 added 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 lose battery or alternator power in flight, your engine will keep running.
Want more power?
Some engines have a turbocharger or a supercharger to enhance the intake stroke and get more out of it.
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