Land-based Gas Turbines are classified into two types: heavy frame engines and aero-derivative engines. Heavy frame engines have low pressure ratios (usually less than 20) and a proclivity for size. The pressure ratio is the ratio of compressor discharge pressure to intake air pressure. Find out more about the working principles of gas turbines, their applications, and compressor and combustor types.
The Operation of a Gas Turbine
Any gas turbine cycle includes intake, compression, expansion, and exhaust. As a fundamental of the gas turbine working principle, the compressor first compresses the air, which is then driven through the combustion engine in each gas turbine type. For high-temperature and high-pressure gas processing, fuel is continuously burned. A gas turbine expands the gas produced by the combustor into the turbine, generating the rotary energy required by the compressor in the preceding stage. The remaining energy is routed through an output shaft.
Applications for Gas Turbines
In terms of gas turbine applications, these turbines are currently one of the most popular technologies for electricity generation. Their energy could also be used in chemical plants and refineries. In recent years, they have made significant contributions to cleaner power generation. The development of new and advanced technologies would allow for more efficient use of gas turbines in a variety of power sectors, from electricity generation to transportation and aviation, thereby improving the efficiency of all of these industries.
Apart from generating electricity in power and chemical plants, turbomachines are also the foundation of modern aviation and aircraft propulsion. Gas turbines of various types are used in aircraft ranging from small passenger planes like the beautiful Hawker 400, formerly known as the MU-300, to the magnificent A380. They are also used in cargo planes ranging in size from small to large, such as the Airbus Beluga. Jet engines are also used to propel military aircraft.
If you look even further back in time, you will find records of jet engines being proposed for locomotive, marine, and automotive propulsion.
Gas Turbine Types
The four major types of gas turbine engines are discussed in this section. Keep in mind that such a wide range of gas turbine designs is only found in aircraft gas turbines. The configuration of gas turbines used in power plants is similar to that of turbojet engines, which will be discussed further below.
Turbojet engines were the first type of gas turbine. Despite their appearance, they operate on the same principles as reciprocal engines: intake, compression, power, and exhaust. Air is moved at high speed to the fuel inlet and ignitor of the combustion chamber in this type of engine. By expanding air, the turbine causes accelerated exhaust gases.
A turboprop engine is the second type of gas turbine. It is a turbojet engine connected to a propeller by a gear system. The operation of a gas turbine of this type is as follows:
- The turbojet drives a shaft that is connected to a transmission gearbox.
- A transmission box slows the spinning process, and the transmission mechanism is attached to the slowest moving gear.
- The air propeller spins and produces thrust.
The best turbojets and turboprops in the world are paired with turbofan engines. A duct fan can connect a turbofan engine to the front of a turbojet engine. The fan then provides additional thrust, aids in engine cooling, and reduces engine noise output.
Turboshaft engines, which are mostly found on helicopters, are the fourth type of gas turbine. The main distinction is that turboshaft engines use the majority of their power to spin turbines rather than driving them out the back of the vehicle. Turboshaft engines are turbojet engines with a large shaft attached to the back.
Gas Turbine Engine Components
A gas-turbine engine can generate useful propellant thrust. In the case of a pure jet engine, this can power a generator, pump, or propeller as well as generate thrust through the nozzle. While the gas turbine engine is a simple system, components for a powerful machine must be carefully constructed and made from expensive materials due to high operating temperatures and stresses. As a result, gas turbine engine installations are typically limited to large units where they are cost effective.
Additionally, gas turbine components are basically: a compressor (takes in and compresses the air), combustor (Fuel is applied to the air and ignited), turbine (converts high-speed gas energy into rotary power through expansion), gearbox and shaft (provides the driven devices with rotary power), and exhaust nozzle (runs out of the turbine part the low emissions of spent gas).
It should be noted that gas turbine gearboxes are quite common in many current gas turbine designs used around the world. Based on its rotational speed and power output, this component is responsible for effectively delivering the turbine’s produced power to the moving parts. However, there are newer designs that have a direct drive configuration, which means that there is no gearbox inside the gas turbine engine and the turbine rotational power is transferred directly to where it is needed.
Gas Turbine Compressor
Whatever gas turbine type you consider, all gas turbines have a compressor that increases input air pressure before entering the combustion engine. The compressor’s output is critical for overall engine efficiency. The compression component of the gas turbine engine’s thermodynamic cycle is provided by gas turbine compressors. There are three types of gas turbine compressors: axial, centrifugal, and mixed flow.
The combustion chamber, also known as the combustor, is an important component of gas turbine engines in which the fuel molecules undergo the exothermic chemical reaction of combustion, also known as burning, which produces a tremendous amount of heat.
The chemical reaction produces a mixture of gases that are not only extremely hot due to the nature of the process, but also have a very high pressure because their parent gases came from the compressor. This causes them to beg to escape the chamber and expand in the turbine.
The mechanical power is generated in the turbine. This mechanical power is produced when hot gases exiting the chamber pass through the turbine blades, causing them to rotate about their axis. This power is now used differently in different design configurations.
In turbofans and turboshafts, the hot gases are expanded further in the turbine to generate more mechanical power to rotate the fans or helicopter blades, which are the primary sources of propulsion for aerial vehicles powered by these engine configurations.
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