6 / 20

During which two strokes of the four-stroke cycle does the piston travel upward from Bottom Dead Centre (BDC) toward Top Dead Centre (TDC)?

  • A

    The induction and compression strokes

  • B

    Compression and power strokes

  • C

    The compression and exhaust strokes

  • D

    The exhaust and power strokes

Refet to figure.
The four strokes in their correct sequence are induction, compression, power, and exhaust:

  • During induction, the piston moves downward from TDC to BDC, drawing the air-fuel charge in through the open inlet valve. 
  • During compression, the piston moves upward from BDC to TDC, compressing the charge with both valves closed, and the spark fires near TDC. 
  • During the power stroke, combustion pressure drives the piston downward from TDC to BDC, delivering work to the crankshaft. 
  • During the exhaust stroke, the piston moves upward from BDC to TDC, expelling the burned gases through the open exhaust valve. The two upward strokes (BDC to TDC) are therefore the compression stroke and the exhaust stroke.

The induction stroke and the compression stroke → INCORRECT. The compression stroke is correctly identified as an upward stroke (BDC to TDC). However the induction stroke is a downward stroke in which the piston moves from TDC to BDC to draw the intake charge into the cylinder through the open inlet valve.

Compression and power strokes → INCORRECT. The compression stroke is correctly identified as an upward stroke. However the power stroke is a downward stroke in which combustion pressure drives the piston from TDC to BDC to deliver work to the crankshaft.

The compression stroke and the exhaust stroke → CORRECT. Both the compression stroke and the exhaust stroke involve the piston travelling upward from BDC toward TDC. 

The exhaust and power strokes → INCORRECT. The exhaust stroke is correctly identified as an upward stroke (BDC to TDC). However the power stroke is a downward stroke where combustion pressure pushes the piston from TDC to BDC.

Your Notes (not visible to others)



This question has appeared on the real examination, you can find the related countries below.