Swept volume in an engine is defined as the volume of air displaced during what movement?

Swept volume, also known as displacement volume, in an engine specifically refers to the volume of air or fuel-air mixture displaced by the movement of the piston within the cylinder. This definition is most accurately represented by the movement of the piston from Top Dead Center (TDC) to Bottom Dead Center (BDC).

During this stroke, the piston travels its full distance within the cylinder, sweeping out a volume equal to the cross-sectional area of the cylinder multiplied by the stroke length. This volume is crucial because it represents the amount of air that can be drawn into the combustion chamber for combustion in a four-stroke engine cycle. Therefore, the correct understanding of swept volume hinges on this specific movement of the piston during the intake or power strokes, as it directly corresponds to the volume of air that is replaced in the cylinder.

The other scenarios presented do not deal with the full movement of the piston through the cylinder, and hence do not represent the complete volume displacement properly defined as swept volume.