Title: Why Do Aircraft Engines Have Two Spark Plugs Per Cylinder? | Boldmethod
Headings: Why Do Aircraft Engines Have Two Spark Plugs Per Cylinder?
Why Do Aircraft Engines Have Two Spark Plugs Per Cylinder?
1) Reliability
2) More Power
3) Even Combustion
https://www.flickr.com/photos/scsibug/
Spark Plug Fouling
AA1Car.com
Two Really Is Better Than One
Colin Cutler
Images Courtesy:

Content: 1) the fuel air mixture burns more quickly, and 2) the fuel air mixture burns more completely. And when you have both of those things happening in your cylinder, you get more power, which is something almost every pilot is looking for. 3) Even Combustion
Combustion is the last major factor in a dual spark plug configuration. When you only have one spark plug per cylinder, the fuel-air mixture burns top-down from the center, moving outward. But when you have two spark plugs on opposite sides of the cylinder, the fuel-air mixture burns from the edges of the cylinder, moving inward. This even burn helps prevent hot-spots in the cylinder, and distributes pressure more evenly across the cylinder, which is important with the big, high-compression, air cooled engines found in most airplanes general aviation airplanes. https://www.flickr.com/photos/scsibug/
Spark Plug Fouling
There's one last benefit to a dual spark plug configuration, and it has to do with spark plug fouling. 100LL Avgas contains lead. And to be more specific, it contains "TEL", or tetraethyllead. TEL is added to avgas to prevent engine knocking (also known as detonation).