In describing an engine or gas compressor, the ratio of volume of working substance actually admitted, measured at specified temperature and pressure, to the full piston displacement volume. For a liquid-fuel engine, such as a diesel engine, volumetric efficiency is the ratio of volume of air drawn into a cylinder to the piston displacement. For a gas-fuel engine, such as a gasoline engine with carburetor, throttle body, or port injection, volumetric efficiency is based on the charge of fuel and air drawn into the cylinder.