In a four-stroke cycle diesel engine, the intake valves open __________.
β’ Valve timing in a four-stroke diesel engine (intake, compression, power, exhaust) β’ Piston positions: TDC (Top Dead Center) and BDC (Bottom Dead Center) β’ Why intake valves often open slightly before or slightly after these dead-center positions
β’ Think about when you want fresh air to start entering the cylinder: should the valve start to open exactly at TDC, or slightly before/after, to get better filling? β’ As the piston moves from TDC to BDC on the intake stroke, does it make sense for the intake valve to close exactly at BDC, or a bit before/after, to keep air flowing? β’ In real engines (not the ideal textbook diagram), are valves timed to open and close exactly at dead centers, or do they lead/lag those positions for efficiency?
β’ Identify which options have the intake valve open during the entire intake stroke (from just before/after TDC to just before/after BDC). β’ Eliminate any option where the valve timing would clearly cut off air too early or start intake too late to fill the cylinder properly. β’ Remember that practical engines usually use valve lead and lag, meaning timing is advanced or retarded slightly from exact TDC/BDC.
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