Mechanical Engineering - Compressors, Gas Dynamics and Gas Turbines - Discussion

Answer is C : Root Blower.

External compression refers to pumps that transfer air at ambient pressure into the engine. If the engine is running under boost conditions, the pressure in the intake manifold is higher than that coming from the supercharger. That causes a backflow from the engine into the supercharger until the two reach equilibrium. It is the backflow that actually compresses the incoming gas. This is an inefficient process and the main factor in the lack of efficiency of Roots superchargers when used at high boost levels. The lower the boost level the smaller is this loss, and Roots blowers are very efficient at moving air at low-pressure differentials, which is what they were invented for (hence the original term "blower").

Centrifugal compressors, sometimes called radial compressors, are a sub-class of dynamic axisymmetric work-absorbing turbomachinery.

They achieve a pressure rise by adding kinetic energy/velocity to a continuous flow of fluid through the rotor or impeller. This kinetic energy is then converted to an increase in potential energy/static pressure by slowing the flow through a diffuser. The pressure rise in the impeller is in most cases almost equal to the rise in the diffuser.

Centrifugal Compressor is most commonly used followed by Roots Blower.

So the answer is C.

Here, Centrifugal Compressor is used normally.

But radial flow compressor are centrifugal.