Solve this multiple-choice question and choose the correct option.

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Effect of compression ratio on knock in petrol (SI) engines: evaluate the statement. Statement: “Detonating (knocking) tendency in petrol engines increases as compression ratio increases.” Choose whether the statement is correct.

Difficulty: Easy

Agree
Disagree
True only at very low speeds
False; higher CR always reduces knock

Correct Answer: Agree

Explanation:

Concept/ApproachHigher compression ratio raises end-gas temperature and pressure, reducing the ignition delay of the end-gas and making auto-ignition (knock) more likely for a given fuel octane. Therefore, knock tendency increases with CR unless higher-octane fuel or mitigating design measures are used.

Final AnswerAgree.

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