Which of the following is an example of a positive displacement air compressor?
Reciprocating piston compressor
Air compressors fall into two broad families based on how they raise pressure:
The distinction between the two families is fundamental:
| Positive displacement | Dynamic (roto-dynamic) |
|---|---|
| Traps a fixed volume of air in a chamber and mechanically reduces that volume to raise pressure | Imparts high velocity (kinetic energy) to the air with an impeller/blades, then converts that velocity into pressure in a diffuser |
| Reciprocating (piston), and rotary types: vane, screw, lobe/Roots | Centrifugal (radial) and axial-flow compressors |
Among the choices, the reciprocating piston compressor is the classic positive-displacement machine: the piston draws air into the cylinder, the valves close to trap a definite volume, and the piston then compresses that trapped charge each stroke. It therefore delivers high pressure ratios in relatively small flow rates.
Why the other choices are wrong: the centrifugal compressor, the radial dynamic compressor, and the axial flow compressor are all dynamic machines. They do not trap and squeeze a fixed pocket of air; instead they accelerate a continuous stream and then decelerate it to build pressure. Hence none of them is a positive-displacement type. (Other positive-displacement machines not listed here include screw, vane and lobe compressors.)
Important Questions from IC Engine Cycles
The pressure of charge inducted through the inlet port inside the cylinder in the case of a two-stroke engine is _______.
From which of the following air standard cycles an Otto cycle may be obtained if constant pressure heat addition is removed?
Lenoir cycle is used for:
The constant volume cycle is also called
_______ engines is work in vacuum
