Valve timing (four-stroke petrol engine): when does the inlet valve open and close? State the most accurate generic timing description (qualitative) for the inlet valve events. Choose the correct option.
Mechanical Engineering
IC Engines and Nuclear Power Plants
Difficulty: Easy
Choose an option
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AOpens slightly before top dead centre (end of exhaust) and closes slightly after bottom dead centre (end of suction)
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BOpens exactly at TDC and closes exactly at BDC
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COpens after TDC during suction and closes at BDC
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DOpens at BDC and closes at the next TDC
Answer
Correct Answer: Opens slightly before top dead centre (end of exhaust) and closes slightly after bottom dead centre (end of suction)
Explanation
ConceptTypical valve timing uses valve lead and valve lag for better volumetric efficiency: the inlet valve usually opens a little before TDC (overlap with exhaust) and closes a little after BDC to take advantage of intake inertia.
Why other options are incorrectExact TDC/BDC opening/closing (Option B) is not used in practice; Options C and D misrepresent the standard timing sequence.
Final AnswerOpens slightly before TDC and closes slightly after BDC.