Page 13 - Automotive Engineering

CH AP TER 1 .1 Piston-engine cycles of operation

Fig. 1.1-3 Four-stroke-cycle petrol engine.

1.1.1.3 Valve timing diagrams the exhaust valve opens before BDC and closes after
TDC. These early and late opening and closing events can
In practice, the events of the four-stroke cycle do not be shown on a valve timing diagram such as Fig. 1.1-4.
start and finish exactly at the two ends of the strokes – to Valve lead This is where a valve opens so many
improve the breathing and exhausting, the inlet valve is degrees of crankshaft rotation before either TDC or
arranged to open before TDC and to close after BDC and BDC.

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