Detonation in spark-ignition engines — primary consequence Which of the following is a significant effect of detonation (knock) during engine operation?

Introduction / Context:
Detonation is the auto-ignition of end-gas after spark, producing pressure waves that ring the combustion chamber. It is harmful to performance and components.

Given Data / Assumptions:

• Spark-ignition petrol engine under high load or advanced timing.
• Low-octane fuel or high intake temperature.
• No pre-ignition assumed (a different fault).

Concept / Approach:
Knock disrupts controlled flame propagation, reducing effective mean pressure and forcing the ECU (if present) to retard timing, both of which reduce power. Prolonged knock also increases thermal and mechanical stresses, risking overheating and damage.

Step-by-Step Solution:
End-gas auto-ignites → pressure oscillations → unstable combustion.Engine control retards ignition to avoid knock → lower torque output.Net result: noticeable loss of power and drivability.

Verification / Alternative check:
Dyno testing with induced knock shows reduced brake mean effective pressure once timing is pulled back.

Why Other Options Are Wrong:
Ignition delay refers to time before combustion starts; knock is not a delay but abnormal rapid combustion.

Overheating can occur but is a secondary consequence; the primary immediate effect felt by a driver is power loss.

Overcooling and improved economy are incorrect.

Common Pitfalls:
Confusing detonation with pre-ignition; using too low octane; excessive intake air temperature; carbon deposits elevating compression.

Final Answer:
loss of power