Which of the following statements regarding preignition and detonation is true?

Preignition and detonation are both critical phenomena in engine operation, particularly in reciprocating engines. Understanding their definitions and implications is essential for effective engine management.

Preignition refers to the premature ignition of the air-fuel mixture before the piston reaches the optimal point in its compression cycle. This can lead to engine knock, reduced performance, and potential damage because the flame propagates at a non-optimal time relative to the engine's timing, causing pressure increases that are undesirable and can harm the engine.

Detonation, on the other hand, occurs when the combustion process does not proceed smoothly. Instead, it causes a rapid spike in pressure and temperature, leading to a knock that can be damaging to engine components. It can occur due to various reasons, including high cylinder pressure, excessive engine temperatures, or the use of fuel with an improper octane rating.

If the statements provided in the question were incorrectly asserting that either preignition or detonation is benign or does not have severe consequences, then that would validate the reasoning for selecting that neither statement is true. This highlights the importance of both understanding the mechanics of these occurrences and recognizing their implications on engine performance and reliability.