Which statement about volumetric efficiency is true?

• A. It cannot exceed 100 percent.
• B. It is the volume of the charge to the area of the cylinder.
• C. It will not be affected by temperature.
• D. Volumetric efficiency may be more than 100 percent in supercharged engines.

Answer: (D)

Volumetric efficiency is about how effectively the engine fills its cylinders with air on the intake stroke. It’s the ratio of the actual air volume that enters the cylinder to the engine’s swept (displacement) volume. In a naturally aspirated engine this ratio is typically 100% or less because the intake pressure and flow limit how much air can be drawn in. But with forced induction, such as a supercharger, the intake pressure is boosted, pushing more air into the cylinder than the displacement would at ambient pressure. That means the volumetric efficiency can exceed 100%. So the statement that volumetric efficiency may be more than 100 percent in supercharged engines is the correct one. The other options are not accurate: the efficiency is a ratio, not simply the charge volume to the cylinder area; it can be affected by temperature since air density changes with temperature; and it can indeed exceed 100% with boosting.