What is preignition in the context of engine operation?

Preignition is defined as the premature ignition of the fuel-air mixture in the combustion chamber of an engine due to the presence of hot spots, such as carbon deposits or excessively hot spark plugs. These hot spots can ignite the mixture before the spark plug fires, leading to a variety of adverse effects including loss of power, increased engine temperatures, and potentially harmful engine knock. This situation can be detrimental as it occurs outside the intended timing of the ignition process, which is finely tuned for optimal engine performance and efficiency. Addressing and preventing preignition involves ensuring that the engine is properly maintained and free from conditions that might create these hot spots.