Pre-ignition vs. detonation in SI engines: evaluate the truth of the statement. Statement: “Pre-ignition occurs before the spark is produced, whereas detonation (knock) develops after the introduction of the spark.” Choose whether this statement is correct or incorrect.

Concept/Approach
Pre-ignition is spontaneous ignition of the mixture before the intended spark event due to hot spots (e.g., glowing deposits, overheated plug). Detonation (knock) is the auto-ignition of the end-gas that occurs after the normal flame is initiated by the spark.

Why the statement is correct
The timing of the phenomena is the key: pre-ignition precedes the spark; knock follows spark initiation.

Final Answer
Agree.