From Air to Power: Understanding the Gas Turbine Engine

Working Principle of Gas Turbine

The compressor, driven by the turbine, continuously draws in air from the atmosphere and compresses and increases its pressure. The compressed air enters the combustion chamber, mixes with the injected fuel and burns. After becoming high-temperature combustion gas, it flows into the turbine to expand and do work. After doing work, the pressure of the combustion gas drops to atmospheric pressure and is discharged into the atmosphere.

Therefore, the three main parts of a gas turbine are the compressor, the combustion chamber and the turbine.

An axial flow compressor has many blades, which are similar in shape to propeller blades, but are divided into “moving blades” and “stationary blades”. The moving blades rotate like a propeller, pushing the airflow backwards during the rotation. At this time, the pressure of the airflow will increase and the temperature will also rise.

The function of the stationary blades is to guide the rotating airflow generated by the action of the moving blades back to the axial direction and enter the next set of rotors at the correct angle. Usually a set of moving blades and a set of stationary blades are configured alternately, and a set of moving blades and a set of stationary blades are called a stage.

In addition, there is a radial compressor. It uses the centrifugal force generated by the rotation of the impeller to push the airflow outward, thereby generating a pressurized effect. A single-stage radial compressor can have the compression ratio of several stages of axial compressors, which is a good choice for smaller gas turbines.

The combustion chamber converts the chemical energy of the fuel into thermal energy, heating the high-pressure air pressed in by the compressor to a high temperature so that it can be expanded in the turbine to do work. The fuel can be liquid fuel (such as gasoline) or gaseous fuel (such as natural gas).

In front of the combustion chamber casing is the air inlet leading to the compressor, and behind is the hot gas outlet leading to the turbine.

The function of the turbine is to convert the energy in high-temperature and high-pressure combustion gas into mechanical energy.

At present, most of the axial flow turbines are used, which are characterized by high power, large flow and high efficiency. The centrifugal turbine is a radial flow turbine, which is mainly used in some small power gas turbines.

A gas turbine is an internal combustion power machine that uses a continuously flowing gas as a working fluid to drive the impeller to rotate at high speed, converting the energy of the fuel into useful work. It is a rotating impeller heat engine.

In the main process of air and gas in a gas turbine, there is only a gas turbine cycle consisting of three major components: a compressor, a combustion chamber, and a gas turbine, which is generally called a simple cycle. Most gas turbines use a simple cycle scheme.

The compressor inhales air from the external atmospheric environment and compresses it step by step through an axial flow compressor to increase the pressure, and the air temperature is also increased accordingly; the compressed air is pressed into the combustion chamber and mixed with the injected fuel to burn to generate high-temperature and high-pressure gas; then it enters the turbine to expand and do work, driving the turbine to drive the compressor and the external load rotor to rotate at high speed, realizing the partial conversion of the chemical energy of the gas or liquid fuel into mechanical work, and outputting electrical work. The exhaust gas discharged from the turbine is discharged to the atmosphere to release heat naturally. In this way, the gas turbine converts the chemical energy of the fuel into thermal energy, and then converts part of the thermal energy into mechanical energy. Usually in a gas turbine, the compressor is driven by the expansion work of the gas turbine, which is the load of the turbine. In a simple cycle, about 1/2 to 2/3 of the mechanical work generated by the turbine is used to drive the compressor, and the remaining 1/3 of the mechanical work is used to drive the generator. When the gas turbine is started, external power is first required. Generally, the starter drives the compressor until the mechanical work generated by the gas turbine is greater than the mechanical work consumed by the compressor. The external starter is tripped and the gas turbine can work independently.