Clearance volume is defined as which space in the cylinder?

• A. Volume below piston at BDC
• B. Space above piston when at TDC
• C. Volume of crankcase
• D. Volume of intake manifold

Answer: (B)

Clearance volume is the gas-filled space inside the cylinder that remains when the piston is at the top of its travel. In other words, it is the space above the piston at the upper dead center position, inside the combustion chamber, between the piston crown and the cylinder head (including any valve pockets). This small volume is what you have to compress along with the incoming charge, and it directly affects the compression ratio: CR = (swept volume + clearance volume) / clearance volume.

The other spaces aren’t part of the clearance: the space below the piston at bottom dead center is the swept volume, not the remaining gas after compression. The crankcase volume and the intake manifold volume are outside the cylinder and do not contribute to the cylinder’s clearance volume.