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SESK: Stuff Everyone Should Know · sesk.info/pilot-preignition-hot-spot

What usually causes preignition in a piston engine?

A hot spot in the combustion chamber lights the mixture early.

  1. Fuel with too high an octane rating
  2. A hot spot in the combustion chamber ✔
  3. Leaving carburetor heat on too long

Why: Preignition means the mixture lights before the spark plug fires. A glowing carbon deposit or cracked spark plug insulator can act like a tiny igniter. It is often hard to tell apart from detonation.

Huh, didn't know that: Detonation and preignition both reduce engine performance, so pilots often cannot tell which one is happening.

The dad joke
Why was the fuel-air mixture always early? It couldn't wait for its spark.
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Sources

  1. FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Chapter 7 https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/faa-h-8083-25c.pdf

Test yourself in the game

Flying & DronesPer the FAA, carburetor icing can occur at outside air temperatures as high as about what?Flying & DronesAs an airplane climbs with the mixture left at full rich, the fuel-air mixture becomes what?Flying & DronesWhat is detonation in a piston aircraft engine?

That's stuff everyone should know.