Valve timing for a four-stroke petrol engine: exhaust valve events Select the correct typical timing for the exhaust valve opening and closing in a four-stroke petrol engine. Choose the correct option.
Mechanical Engineering
IC Engines and Nuclear Power Plants
Difficulty: Medium
Choose an option
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AOpens at 50° before BDC and closes at 15° after TDC
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BOpens at BDC and closes at TDC
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COpens at 50° after BDC and closes at 15° before TDC
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DMay open and close anywhere
Answer
Correct Answer: Opens at 50° before BDC and closes at 15° after TDC
Explanation
ConceptTypical valve timing uses early exhaust opening (≈ 40–60° before BDC) for blow-down, and exhaust closing slightly after TDC (≈ 10–20°) to aid scavenging and benefit from exhaust inertia.
Why A is rightThe given pair (≈ 50° before BDC / 15° after TDC) lies within common textbook values.
Final AnswerOpens at 50° before BDC and closes at 15° after TDC