Which statement is true about volumetric efficiency under boosted conditions?

• A. It is always less than 100 percent.
• B. It cannot be more than 100 percent.
• C. It depends on engine speed only.
• D. It may be more than 100 percent in supercharged engines.

Answer: (D)

Under boosted conditions, the intake charge is pressurized by a supercharger or turbocharger, increasing air density inside the cylinder. Volumetric efficiency measures how effectively the engine fills its cylinders with air relative to their displacement. Because the air entering the cylinders is at a higher pressure than atmospheric, more air mass can be packed into the same cylinder volume per cycle than would occur at standard pressure. This can push volumetric efficiency above 100 percent, since the actual air inducted can exceed the amount that would fill the displacement at ambient pressure. Engine speed influences VE too, but boosting changes the filling amount independently of speed, so VE can indeed be greater than 100 percent in supercharged engines.