What causes spark plug fouling in an aircraft engine?

Spark plug fouling in an aircraft engine occurs primarily due to an excessively rich fuel mixture. When the mixture is too rich, it means there is more fuel than air entering the combustion chamber. This results in incomplete combustion, leading to the accumulation of fuel residue, carbon deposits, and oil on the spark plugs. Over time, these deposits can cause the spark plugs to misfire, leading to engine performance issues.

In contrast, high RPM operation tends to create a better combustion environment due to the increased air and fuel flow, which reduces the likelihood of fouling. High cylinder head temperatures can promote more efficient combustion as well, preventing deposits from forming. Low engine temperatures, while they can impact performance, are not the primary cause of spark plug fouling caused by a rich fuel mix.