Spark timing in a four-stroke petrol (SI) engine: identify the usual ignition timing. Choose the standard practice for when the charge is ignited relative to top/bottom dead centre (TDC/BDC).
Mechanical Engineering
IC Engines and Nuclear Power Plants
Difficulty: Easy
Choose an option
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A30° before top dead centre
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B30° after top dead centre
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C30° before bottom dead centre
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D30° after bottom dead centre
Answer
Correct Answer: 30° before top dead centre
Explanation
Concept/ApproachTo allow flame development and complete combustion near TDC, spark timing is advanced. Typical advance is of the order of 10°–30° before TDC depending on speed/load.
Final Answer30° before top dead centre (representative textbook value).