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Concept
Compressor
Summary
A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor.
Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. The main distinction is that the focus of a compressor is to change the density or volume of the fluid, which is mostly only achievable on gases. Gases are compressible, while liquids are relatively incompressible, so compressors are rarely used for liquids. The main action of a pump is to pressurize and transport liquids.
Many compressors can be staged, that is, the fluid is compressed several times in steps or stages, to increase discharge pressure. Often, the second stage is physically smaller than the primary stage, to accommodate the already compressed gas without reducing its pressure. Each stage further compresses the gas and increases its pressure and also temperature (if inter cooling between stages is not used).
The main and important types of gas compressors are illustrated and discussed below:
A positive displacement compressor is a system that compresses the air by the displacement of a mechanical linkage reducing the volume (since the reduction in volume due to a piston in thermodynamics is considered as positive displacement of the piston).
Put another way, a positive displacement compressor is one that operates by drawing in a discrete volume of gas from its inlet then forcing that gas to exit via the compressor's outlet. The increase in the pressure of the gas is due, at least in part, to the compressor pumping it at a mass flow rate which cannot pass through the outlet at the lower pressure and density of the inlet.
Reciprocating compressor
Reciprocating compressors use pistons driven by a crankshaft. They can be either stationary or portable, can be single or multi-staged, and can be driven by electric motors or internal combustion engines. Small reciprocating compressors from 5 to 30 horsepower (hp) are commonly seen in automotive applications and are typically for intermittent duty.
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Turbojet
The turbojet is an airbreathing jet engine which is typically used in aircraft. It consists of a gas turbine with a propelling nozzle. The gas turbine has an air inlet which includes inlet guide vanes, a compressor, a combustion chamber, and a turbine (that drives the compressor). The compressed air from the compressor is heated by burning fuel in the combustion chamber and then allowed to expand through the turbine. The turbine exhaust is then expanded in the propelling nozzle where it is accelerated to high speed to provide thrust.
Intercooler
An intercooler is a heat exchanger used to cool a gas after compression. Often found in turbocharged engines, intercoolers are also used in air compressors, air conditioners, refrigeration and gas turbines. Most commonly used with turbocharged engines, an intercooler is used to counteract the heat of compression and heat soak in the pressurised intake air. By reducing the temperature of the intake air, the air becomes denser (allowing more fuel to be injected, resulting in increased power) and less likely to suffer from pre-ignition or knocking.
Internal combustion engine
An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is typically applied to pistons (piston engine), turbine blades (gas turbine), a rotor (Wankel engine), or a nozzle (jet engine).