<\/a><\/noindex>*Here and further, we will be discussing subsonic speeds. At supersonic speeds, the physics changes, and everything is quite different. <\/p>\n
The compressor is a device that increases the pressure of the air. A compressor can be characterized by a parameter known as pressure ratio. In modern engines, it already exceeds 40 units. Additionally, the temperature within it increases (up to about 400 degrees Celsius).<\/p>\n
The combustion chamber is a device where heat from fuel combustion is supplied to compressed air (after the compressor). The temperature in the combustion chamber is very high, reaching up to 2000 degrees Celsius. You might think that the gas pressure in the chamber also increases significantly, but that's not the case. Theoretically, it is considered that heat is supplied at constant pressure. In reality, it falls slightly due to losses (a problem of design imperfection). <\/p>\n
A turbine is a device that converts part of the energy of gas after the combustion chamber into the energy needed to drive the compressor. Since turbines are used not only in aviation, a more general definition can be given: it is a device that converts the internal energy of the working medium (in this case, the working medium is gas) into mechanical work on the shaft. As you might understand, the turbine and compressor are on the same shaft and are rigidly connected. If the pressure of gas in the compressor increases, then in the turbine, conversely, it decreases, meaning the gas expands. <\/p>\n
A nozzle is a narrowing channel in which the potential energy of gas is transformed into kinetic energy (the remaining energy reserve of the gas after the turbine). As in the turbine, gas expansion occurs in the nozzle. A jet is formed, which, flowing out of the nozzle, propels the aircraft. <\/p>\n
We have covered the main elements. But still, it\u2019s not very clear how it works? Then let\u2019s go over it once more briefly. <\/p>\n
Air from the atmosphere enters the intake device, where it is slightly compressed and sent to the compressor. In the compressor, the air pressure increases even further, raising the temperature. After the compressor, the air enters the combustion chamber and ignites as it mixes with fuel, resulting in a significant increase in temperature at what can be considered constant pressure. After the combustion chamber, the hot compressed gas enters the turbine. Part of the gas's energy is used to rotate the compressor via the turbine (so it can perform its function described above), while another part of the energy is used for the necessary movement of the aircraft, as the gas, after passing through the turbine, transforms into a jet stream in the nozzle and rushes out of it into the atmosphere. Thus, the cycle concludes. Of course, in reality, all processes of the cycle occur continuously.<\/p>\n
This cycle is called the Brayton cycle, or the thermodynamic cycle with a continuous working process and heat supply at constant pressure. All gas turbine engines operate on this cycle.<\/p>\n
The Brayton cycle in P-V coordinates<\/i><\/p>\n
H-B \u2014 compression process in the intake device
Schematic design of a turbojet engine, where 0-0 is the engine axis<\/i><\/p>\n
A turbojet engine may have two shafts. In this case, the compressor consists of a low-pressure compressor (LPC) and a high-pressure compressor (HPC), while the work is performed by the low-pressure turbine (LPT) and high-pressure turbine (HPT) respectively. This scheme is more advantageous from a gas dynamics perspective.<\/p>\n
A real engine of this type in cross-section<\/i><\/p>\n
We have examined the operating principle of the simplest scheme of an aviation gas turbine engine. Naturally, modern \"Airbus and Boeing\" aircraft are equipped with turbojet engines whose design is significantly more complex, but they operate according to the same principles. Let\u2019s take a look at them.<\/p>\n
Dual-circuit turbojet engine<\/h2>\n \nThe turbofan engine (\u0422\u0420\u0414\u0414) primarily differs from the turbojet engine (\u0422\u0420\u0414) in that it has two circuits: an external and an internal one. The internal circuit contains the same components as the turbojet: a compressor (divided into high-pressure and low-pressure), a combustion chamber, a turbine (divided into high-pressure and low-pressure), and a nozzle. The external circuit consists of a duct with a nozzle at the end. It does not contain a combustion chamber or turbine. Before both circuits (immediately after the engine's intake device) is a compressor stage designed to work on both circuits. <\/p>\n
It's quite a perplexing picture, isn't it? Let's break down how it works.<\/p>\n
Schematic diagram of a two-shaft dual-circuit turbojet engine.<\/i><\/p>\n
Air entering the engine, after passing through the first stage of the low-pressure compressor, splits into two streams. One part of the air goes through the internal circuit, where the same processes occur as described when examining the turbojet. The second part of the air enters the external circuit, gaining energy from the first stage of the low-pressure compressor (the one that operates on both circuits). In the external circuit, the energy of the air is spent only on overcoming hydraulic losses (due to friction). Eventually, this air reaches the nozzle of the external circuit, creating immense thrust. The thrust generated by the external circuit can constitute 80% of the total engine thrust. <\/p>\n
One of the most critical characteristics of a turbofan engine is the bypass ratio. The bypass ratio is the ratio of air flow in the external circuit to the air flow in the internal circuit. This number can be either greater than or less than one. In modern engines, this number exceeds 12.
Turbojet engine (\u0422\u0420\u0414\u0414) of the Boeing 757-200. The intake device and fan are visible in the foreground.<\/i><\/p>\n
In some engines, the fan is driven by a separate turbine located closest to the nozzle of the internal circuit. This results in a three-shaft engine. For example, this configuration is used in the Rolls Royce RB211 engines (installed on L1011, B747, B757, B767), D-18T (An-124), D-36 (Yak-42).<\/p>\n
D-18T cross-section from the inside.<\/i><\/p>\n
The main advantage of the turboprop engine lies in its ability to generate high thrust and good fuel efficiency compared to turbojet engines. <\/p>\n
With this, I would like to conclude the discussion on turboprop engines and move on to the next type of engine \u2014 piston engines.<\/p>\n
Turboprop Engines<\/h2>\n \nA turboprop engine, like a turbojet engine, is classified as a gas turbine engine. It operates almost like a turbojet. A basic turboprop engine consists of familiar components: a compressor, a combustion chamber, a turbine, and a nozzle. It also includes a gearbox and a propeller. <\/p>\n
Schematic Diagram of a Piston Engine<\/i><\/p>\n
There is also another design of turboprop engines: with a free turbine.
Schematic Diagram of a Piston Engine with a Free Turbine<\/i><\/p>\n
I want to emphasize that turboprop engines should not be viewed as an inefficient relic of the past. I have heard such statements several times, but they are incorrect.
This concludes our discussion on turboprop engines. We are gradually moving towards the concept of a turboshaft engine.<\/p>\n
Turboshaft Engine<\/h2>\n \nIt is likely that most readers are hearing this name for the first time. This type of engine is primarily used in helicopters. <\/p>\n
The turboshaft engine is very similar to the turboprop engine with a free turbine. It also consists of a compressor, combustion chamber, compressor turbine, followed by a free turbine, which is only gas dynamically linked to the entire preceding system. However, it does not generate jet thrust, as it lacks a jet nozzle, only producing exhaust. The free turbine has its own shaft that connects to the helicopter's main rotor gearbox. Yes, all helicopters I am familiar with have such a gearbox, which is typically quite large. The reason is that the rotor speed of a helicopter is very low. For an airplane, as I mentioned earlier, it can reach 1500 RPM, while a helicopter, such as the Mi-8, achieves only 193 RPM.
Schematic Design of a Turboshaft Engine<\/i><\/p>\n
The TV3-117 engine from the Mi-8 helicopter. The exhaust pipe and drive shaft are visible on the right.<\/i><\/p>\n
We have looked at four types of gas turbine engines. I hope my text was clear and useful to you. Please feel free to post any questions or comments. <\/p>\n
Thank you for your attention.habr.com<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"\u0412\u0441\u0435\u043c \u043f\u0440\u0438\u0432\u0435\u0442! \u0412 \u044d\u0442\u043e\u0439 \u0441\u0442\u0430\u0442\u044c\u0435 \u044f \u0445\u043e\u0447\u0443 \u0440\u0430\u0441\u0441\u043a\u0430\u0437\u0430\u0442\u044c \u043e \u0442\u043e\u043c, \u043a\u0430\u043a \u0440\u0430\u0431\u043e\u0442\u0430\u044e\u0442 \u0430\u0432\u0438\u0430\u0446\u0438\u043e\u043d\u043d\u044b\u0435 \u0433\u0430\u0437\u043e\u0442\u0443\u0440\u0431\u0438\u043d\u043d\u044b\u0435 \u0434\u0432\u0438\u0433\u0430\u0442\u0435\u043b\u0438 (\u0413\u0422\u0414). \u042f \u043f\u043e\u0441\u0442\u0430\u0440\u0430\u044e\u0441\u044c \u0441\u0434\u0435\u043b\u0430\u0442\u044c \u044d\u0442\u043e \u043d\u0430\u0438\u0431\u043e\u043b\u0435\u0435 \u043f\u0440\u043e\u0441\u0442\u044b\u043c \u0438 \u043f\u043e\u043d\u044f\u0442\u043d\u044b\u043c \u044f\u0437\u044b\u043a\u043e\u043c. \u0410\u0432\u0438\u0430\u0446\u0438\u043e\u043d\u043d\u044b\u0435 \u0413\u0422\u0414 \u043c\u043e\u0436\u043d\u043e \u043c\u043e\u0436\u043d\u043e \u0440\u0430\u0437\u0434\u0435\u043b\u0438\u0442\u044c \u043d\u0430: \u0442\u0443\u0440\u0431\u043e\u0440\u0435\u0430\u043a\u0442\u0438\u0432\u043d\u044b\u0435 \u0434\u0432\u0438\u0433\u0430\u0442\u0435\u043b\u0438 (\u0422\u0420\u0414) \u0434\u0432\u0443\u0445\u043a\u043e\u043d\u0442\u0443\u0440\u043d\u044b\u0435 \u0442\u0443\u0440\u0431\u043e\u0440\u0435\u0430\u043a\u0442\u0438\u0432\u043d\u044b\u0435 \u0434\u0432\u0438\u0433\u0430\u0442\u0435\u043b\u0438 (\u0422\u0420\u0414\u0414) \u0422\u0443\u0440\u0431\u043e\u0432\u0438\u043d\u0442\u043e\u0432\u044b\u0435 \u0434\u0432\u0438\u0433\u0430\u0442\u0435\u043b\u0438 (\u0422\u0412\u0414) \u0422\u0443\u0440\u0431\u043e\u0432\u0430\u043b\u044c\u043d\u044b\u0435 \u0434\u0432\u0438\u0433\u0430\u0442\u0435\u043b\u0438 (\u0422\u0412\u0430\u0414) \u041f\u0440\u0438\u0442\u043e\u043c, \u0422\u0420\u0414 \u0438 \u0422\u0420\u0414\u0414 \u043c\u043e\u0433\u0443\u0442 \u0441\u043e\u0434\u0435\u0440\u0436\u0430\u0442\u044c \u0432 \u0441\u0435\u0431\u0435 \u0444\u043e\u0440\u0441\u0430\u0436\u043d\u0443\u044e \u043a\u0430\u043c\u0435\u0440\u0443, \u0432 […]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[702],"tags":[],"class_list":["post-35229","post","type-post","status-publish","format-standard","hentry","category-news"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t
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