FAA Powerplant Written Practice Test

What does a spark plug's heat range determine?

1. The amount of fuel burned

2. The spark timing accuracy

3. Its ability to transfer heat to the cylinder head

4. The size of the electrode

The correct answer is: Its ability to transfer heat to the cylinder head

The heat range of a spark plug refers to its ability to transfer heat away from the tip, where combustion occurs, to the cylinder head. This characteristic is crucial because it affects how effectively the spark plug can handle the temperatures generated in the combustion chamber. If a spark plug operates too hot, it may lead to pre-ignition or detonation, which can damage the engine. Conversely, if it is too cold, it may not reach the necessary temperature for proper combustion, leading to fouling due to unburned fuel deposits. A spark plug's design includes various features like the length and diameter of the ceramic insulator, the material and size of the electrode, and the configuration of the plug, all of which are related to its heat transfer capabilities. Therefore, when we refer to the heat range, we are specifically addressing how well the spark plug can manage heat in relation to the engine's operational requirements.