Engine abnormal sounds: The loud, sharp, pulsating noise observed within an internal combustion engine cylinder due to rapid pressure rise of end-gas is called ________.

Introduction / Context:
Engines can exhibit abnormal combustion that creates distinctive noises. Recognizing whether the sound is detonation (knock) or something else is vital for protecting the engine and improving performance.

Given Data / Assumptions:

• A spark-ignition engine operating under load.
• End-gas may auto-ignite after the spark-initiated flame begins to propagate.
• Mechanical noise is distinguished from combustion-induced knock.

Concept / Approach:
Detonation (knock) is spontaneous combustion of the unburned end-gas ahead of the flame front, creating strong pressure waves that ring the combustion chamber. This causes a characteristic metallic, pulsating knock. Turbulence is a flow property aiding flame speed; pre-ignition is early ignition due to hot spots; supercharging increases intake density and is not a noise phenomenon.

Step-by-Step Solution:

Verification / Alternative check:
Knock sensors detect characteristic vibration frequencies linked to resonant modes of the cylinder, confirming the detonation mechanism.

Why Other Options Are Wrong:

• Turbulence: Enhances combustion stability, not a noise source by itself.
• Pre-ignition: Earlier-than-spark ignition; may not create the same ringing knock signature.
• Supercharging: A hardware/operating condition, not a noise type.

Common Pitfalls:
Assuming any loud engine noise is “knock.” Mechanical issues (e.g., bearings) can also be noisy; diagnosis should consider timing and load correlation.

Final Answer:
detonation