Jet engine: principle of operation (briefly). The principle of operation of an aircraft jet engine

- Turboprop.

Such engines allow large aircraft to fly at acceptable speeds and use less fuel.

Two-blade turboprop engine

- Turbofan jet engine.

This type of engine is a more economical relative of the classic type. the main difference is that the input is set larger diameter fan, to which supplies air not only to the turbine, but alsocreates a sufficiently powerful flow outside of it. Thus, increased efficiency is achieved by improving efficiency.

As early as the beginning of the 20th century. Russian scientist K.E. Tsiolkovsky predicted that after the era of propeller-driven airplanes, the era of jet airplanes would come. He believed that only with a jet engine could supersonic speeds be reached.

In 1937, the young and talented designer A.M. Lyulka proposed the project of the first Soviet turbojet engine. According to his calculations, such an engine could accelerate the aircraft to unprecedented speeds at that time - 900 km / h! It seemed fantastic, and the proposal of the young designer was treated with caution. But, nevertheless, work on this engine began, and by the middle of 1941 it was almost ready. However, the war began, and the design bureau where A.M. Lyulka, was evacuated deep into the USSR, and the designer himself was switched to work on tank engines.

But A.M. Lyulka was not alone in his desire to create a jet aircraft engine. Just before the war, engineers from the design bureau V.F. Bolkhovitinov - A.Ya. Bereznyak and A.M. Isaev - proposed the project of the BI-1 fighter-interceptor with a liquid-propellant jet engine.

The project was approved, and the designers set to work. Despite all the difficulties of the first period of the Great Patriotic War, the experienced "BI-1" was nevertheless built.

On May 15, 1942, the world's first rocket fighter was hoisted into the air by an EY test pilot. Bakhchivandzhi. The tests continued until the end of 1943 and, unfortunately, ended in disaster. In one of the test flights, Bakhchivandzhi reached a speed of 800 km / h. But at this speed, the plane suddenly went out of control and rushed to the ground. New car and her brave tester perished.

The first jet-powered aircraft "Messer-schmitt Me-262" appeared in the sky just before the end of the Second World War. It was produced in well-camouflaged factories located in the forest. One of these factories in Gorgau - 10 km west of Augsburg on the autobahn - supplied the wings, nose and tail sections of the aircraft to another "forest" plant nearby, which carried out the final assembly and lifted the finished aircraft directly from the autobahn. The roof of the buildings was painted green, and it was almost impossible to detect such a "forest" plant from the air. Although the Allies managed to detect the Me-262 take-offs and bombed several uncovered planes, they were able to establish the location of the plant only after they had occupied the forest.

The Englishman Frank Whittle, the discoverer of the jet engine, received his patent back in 7930. The first jet the Gloster aircraft was built in 1941 and was tested in May. The government abandoned it - not powerful enough. Only the Germans fully revealed the potential of this invention, in 1942 they assembled the Messerschmitt Me-262, on which they fought until the end of the war. The first Soviet jet aircraft was the MiG-9, and its "descendant" - the MiG-15 - wrote many glorious pages in the combat history of the Korean War (1950-1953).

In the same years, in fascist Germany, which had lost air superiority on the Soviet-German front, work on jet aircraft was being developed more and more intensively. Hitler hoped that with the help of these aircraft he would again seize the initiative in the war and achieve victory.

In 1944, the Messerschmitt Me-262, equipped with a jet engine, was put into mass production and soon appeared at the front. German pilots were very wary of this unusual machine, which did not have the usual propeller. In addition, at a speed close to 800 km / h, it was pulled into a dive, and it was impossible to get the car out of this state. Further, the strictest instructions appeared in the aviation units - in no case should the speed be increased to 800 km / h.

Nevertheless, even with such a limitation, the Me-262 outperformed all other fighters of those years in speed. This allowed the commander of the Nazi fighter aviation, General Holland, to declare that the Me-262 was "the only chance to organize real resistance to the enemy."

On the Eastern Front"Me-262" appeared at the very end of the war. In this regard, the design bureaus received an urgent task to create devices for combating German jet aircraft.

A.I. Mikoyan and P.O. Sukhoi, to help the conventional piston motor located in the bow of the apparatus, added a motor-compressor motor designed by K.V. Kholshchevnikov, installing it in the tail of the aircraft. An additional engine had to be started when the aircraft needed to be given significant acceleration. This was dictated by the fact that the K.V. Kholshchevnikov worked no more than three to five minutes.

The first to finish work on the high-speed fighter A.I. Mikoyan. His I-250 aircraft flew in March 1945. During the tests of this machine, a record speed of 820 km / h was recorded, which was first achieved in the USSR. Fighter P.O. The Sukhoi Su-5 entered testing in April 1945, and after turning on the additional tail engine, a speed exceeding 800 km / h was obtained.

However, the circumstances of those years did not allow the launch of new high-speed fighters into mass production. Firstly, the war ended, even the vaunted Me-262 did not help the Nazis regain their lost air superiority.

Secondly, the skill of Soviet pilots made it possible to prove to the whole world that even jet aircraft can be shot down by flying an ordinary serial fighter.

In parallel with the development of an aircraft equipped with a “pushing” motor-compressor engine, the design bureau of P.O. Sukhoi, the Su-7 fighter was created, in which, together with a piston engine, the liquid-jet RD-1, developed by designer V.P. Glushko.

Flights on the Su-7 began in 1945. Its pilot G. Komarov tested it. When the "RD-1" was turned on, the aircraft's speed increased by an average of 115 km / h. This was a good result, but soon the tests had to be stopped due to the frequent failure of the jet engine.

A similar situation has developed in the design bureaus of S.A. Lavochkin and AS. Yakovlev. On one of the prototype La-7R aircraft, the accelerator exploded in flight, the test pilot miraculously managed to escape. But when testing the Yak-3 with the RD-1 accelerator, the plane exploded and its pilot died. The frequent accidents led to the fact that the tests of aircraft with the "RD-1" were terminated. In addition, it became clear that piston engines were to be replaced by new engines - jet engines.

After the defeat of Germany, German jet aircraft with engines were taken as trophies of the USSR. The Western allies got not only samples of jet aircraft and their engines, but also their developers and equipment from fascist factories.

To gain experience in jet aircraft construction, it was decided to use German JUMO- 004" and "BMW-003", and then create your own based on them. These engines were named "RD-10" and "RD-20". In addition, designers A.M. Lyulke, A.A. Mikulin, V.Ya. Klimov was instructed to create a "completely Soviet" aircraft jet engine.

While the "engines" were working, P.O. Sukhoi developed the Su-9 jet fighter. Its design was made according to the scheme of twin-engine aircraft - two captured JUMO-004 (RD-10) engines were placed under the wings.

Ground tests of the RA-7 jet engine were carried out on the airfield of the airfield in Tushino. While working, he made a terrible noise and threw out clouds of smoke and fire from his nozzle. The roar and glow from the flames were noticeable even at the Moscow Sokol metro station. Not without curiosity. Once, several fire engines rushed to the airfield, called by Muscovites to put out the fire.

The Su-9 aircraft could hardly be called just a fighter. The pilots usually called it a "heavy fighter", since a more accurate name - a fighter-bomber - appeared only by the middle of the 50s. But in its powerful cannon and bomb weapons"Su-9" could well be considered the prototype of such an aircraft.

This arrangement of motors had both disadvantages and advantages. The disadvantages include the large frontal resistance created by the motors located under the wings. But on the other hand, the placement of engines in special outboard engine nacelles opened up unhindered access to them, which was important during repairs and adjustments.

In addition to jet engines, the Su-9 aircraft contained a lot of "fresh" design solutions. So, for example, P.O. Sukhoi installed on his aircraft a stabilizer controlled by a special electromechanism, starting powder boosters, an ejection seat for the pilot and a device for emergency resetting a lantern covering the cockpit, air brakes with a landing shield, and a braking parachute. We can say that the Su-9 was entirely created from innovations.

Soon an experimental version of the Su-9 fighter was built. However, attention was drawn to the fact that the execution of turns on it is physically difficult for the pilot.

It became obvious that with increasing speeds and flight altitude it would be more and more difficult for the pilot to cope with control, and then a new device was introduced into the aircraft control system - a booster amplifier, similar to a power steering. But in those years, the use of a complex hydraulic device on an aircraft caused controversy. Even experienced aircraft designers were skeptical of him.

And yet the booster was installed on the Su-9. Sukhoi was the first to completely shift efforts from the aircraft control sticks to the hydraulic system. The positive reaction of the pilots was not long in coming. Aircraft control has become more pleasant and not tiring. The maneuver was simplified and became possible at all flight speeds.

It should be added that in order to achieve the perfection of the design, P.O. Sukhoi "lost" in the competition between the bureaus of Mikoyan and Yakovlev. The first jet fighters of the USSR - "MiG-9" and "Yak-15" took off on the same day - April 26, 1946. They took part in the air parade in Tushino and were immediately put into production. And the Su-9 appeared in the air only in November 1946. However, the military liked it very much and in 1947 it was recommended for mass production. But he did not go into the series - aircraft factories were already loaded with work on the production of jet MiGs and Yakovs. Yes, and P.O. By that time, Dry was already finishing work on a new, more advanced machine - the Su-11 fighter.

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A jet engine is an engine that creates the traction force necessary for movement by converting the internal energy of the fuel into the kinetic energy of the jet stream of the working fluid.

The working fluid flows out of the engine at high speed, and, in accordance with the law of conservation of momentum, a reactive force is formed that pushes the engine in the opposite direction. To accelerate the working fluid, both the expansion of a gas heated in one way or another to a high thermal temperature (the so-called thermal jet engines) and other physical principles, for example, the acceleration of charged particles in an electrostatic field (see ion engine), can be used.

A jet engine combines the engine itself with a propeller, that is, it creates traction only through interaction with the working fluid, without support or contact with other bodies. For this reason, it is most commonly used to propel aircraft, rockets, and spacecraft.

In a jet engine, the thrust force necessary for movement is created by converting the initial energy into the kinetic energy of the working fluid. As a result of the expiration of the working fluid from the engine nozzle, a reactive force is formed in the form of recoil (jet). The recoil moves the engine and the device structurally connected with it in space. The movement occurs in the direction opposite to the outflow of the jet. Various types of energy can be converted into the kinetic energy of a jet stream: chemical, nuclear, electrical, solar. The jet engine provides its own movement without the participation of intermediate mechanisms.

To create jet thrust, a source of initial energy is needed, which is converted into the kinetic energy of a jet stream, a working fluid ejected from the engine in the form of a jet stream, and the jet engine itself, which converts the first type of energy into the second.

The main part of a jet engine is the combustion chamber, in which the working fluid is created.

All jet engines are divided into two main classes, depending on whether they use the environment in their work or not.

The first class is jet engines (WFD). All of them are thermal, in which the working fluid is formed during the oxidation reaction of a combustible substance with oxygen from the surrounding air. The main mass of the working fluid is atmospheric air.

In a rocket engine, all components of the working fluid are on board the apparatus equipped with it.

There are also combined engines that combine both of the above types.

For the first time, jet propulsion was used in Heron's ball, the prototype of a steam turbine. Solid fuel jet engines appeared in China in the 10th century. n. e. Such rockets were used in the East, and then in Europe for fireworks, signaling, and then as combat ones.

An important stage in the development of the idea of ​​jet propulsion was the idea of ​​using a rocket as an engine for an aircraft. It was first formulated by the Russian revolutionary N. I. Kibalchich, who in March 1881, shortly before his execution, proposed a scheme for an aircraft (rocket plane) using jet thrust from explosive powder gases.

N. E. Zhukovsky in his works "On the reaction of outflowing and inflowing fluid" (1880s) and "On the theory of ships set in motion by the reaction force of outflowing water" (1908) first developed the main issues of the theory of a jet engine.

Interesting work on the study of rocket flight also belongs to the famous Russian scientist I. V. Meshchersky, in particular in the field of the general theory of the motion of bodies of variable mass.

In 1903, K. E. Tsiolkovsky, in his work "Investigation of the World Spaces with Reactive Devices", gave a theoretical justification for the flight of a rocket, as well as a schematic diagram of a rocket engine, which anticipated many of the fundamental and design features of modern liquid-propellant rocket engines (LRE). So, Tsiolkovsky provided for the use of liquid fuel for a jet engine and its supply to the engine with special pumps. He proposed to control the flight of the rocket by means of gas rudders - special plates placed in a jet of gases emitted from the nozzle.

A feature of a liquid-propellant engine is that, unlike other jet engines, it carries with it the entire supply of oxidizer along with the fuel, and does not take the oxygen-containing air necessary for burning fuel from the atmosphere. This is the only engine that can be used for ultra-high-altitude flight outside the earth's atmosphere.

The world's first rocket with a liquid-propellant rocket engine was created and launched on March 16, 1926 by the American R. Goddard. It weighed about 5 kilograms, and its length reached 3 m. Goddard's rocket was fueled by gasoline and liquid oxygen. The flight of this rocket lasted 2.5 seconds, during which it flew 56 m.

Systematic experimental work on these engines began in the 30s of the XX century.

The first Soviet rocket engines were designed and built in 1930–1931. in the Leningrad Gas Dynamic Laboratory (GDL) under the guidance of the future academician V.P. Glushko. This series was called ORM - an experienced rocket motor. Glushko applied some novelties, for example, cooling the engine with one of the fuel components.

In parallel, the development of rocket engines was carried out in Moscow by the Jet Propulsion Study Group (GIRD). Its ideological inspirer was F. A. Zander, and the organizer was the young S. P. Korolev. Korolev's goal was to build a new rocket apparatus - a rocket plane.

In 1933, F.A. Zander built and successfully tested the OR1 rocket engine, which ran on gasoline and compressed air, and in 1932–1933. - engine OP2, on gasoline and liquid oxygen. This engine was designed to be installed on a glider that was supposed to fly as a rocket plane.

In 1933, the first Soviet liquid-fuel rocket was created and tested at GIRD.

Developing the work begun, Soviet engineers subsequently continued to work on the creation of liquid-propellant jet engines. In total, from 1932 to 1941, 118 designs of liquid-propellant jet engines were developed in the USSR.

In Germany in 1931, rockets were tested by I. Winkler, Riedel, and others.

The first flight on a rocket-propelled aircraft with a liquid-propellant engine was made in the Soviet Union in February 1940. An LRE was used as the power plant of the aircraft. In 1941, under the leadership of the Soviet designer V.F. Bolkhovitinov, the first jet aircraft was built - a fighter with a liquid-propellant engine. His tests were carried out in May 1942 by pilot G. Ya. Bakhchivadzhi.

At the same time, the first flight of a German fighter with such an engine took place. In 1943, the United States tested the first American jet aircraft, on which a liquid-propellant engine was installed. In Germany, in 1944, several fighters with these Messerschmitt-designed engines were built and in the same year they were used in a combat situation on the Western Front.

In addition, liquid propellant rocket engines were used on German V2 rockets, created under the direction of W. von Braun.

In the 1950s, liquid rocket engines were installed on ballistic missiles, and then on artificial satellites of the Earth, the Sun, the Moon and Mars, automatic interplanetary stations.

The rocket engine consists of a combustion chamber with a nozzle, a turbopump unit, a gas generator or a steam-gas generator, an automation system, control elements, an ignition system and auxiliary units (heat exchangers, mixers, drives).

The idea of ​​jet engines has been put forward more than once in different countries. The most important and original works in this respect are the studies carried out in 1908–1913. French scientist R. Loren, who, in particular, in 1911 proposed a number of schemes for ramjet engines. These engines use atmospheric air as an oxidizer, and the air in the combustion chamber is compressed by dynamic air pressure.

In May 1939, the first test of a rocket with a ramjet engine designed by P. A. Merkulov took place in the USSR. It was a two-stage rocket (the first stage was a powder rocket) with a takeoff weight of 7.07 kg, and the weight of fuel for the second stage of a ramjet engine was only 2 kg. During the test, the rocket reached a height of 2 km.

In 1939–1940 for the first time in the world in the Soviet Union, summer tests of jet engines installed as additional engines on an aircraft designed by N.P. Polikarpov were carried out. In 1942, ramjet engines designed by E. Senger were tested in Germany.

The jet engine consists of a diffuser in which air is compressed due to the kinetic energy of the oncoming air flow. Fuel is injected into the combustion chamber through the nozzle and the mixture ignites. The jet stream exits through the nozzle.

The operation of the WFD is continuous, so there is no starting thrust in them. In this regard, at flight speeds less than half the speed of sound, jet engines are not used. The use of WFD is most effective at supersonic speeds and high altitudes. The takeoff of an aircraft with a jet engine is carried out using solid or liquid propellant rocket engines.

Another group of jet engines, turbocompressor engines, has received more development. They are divided into turbojet, in which thrust is created by a jet of gases flowing from a jet nozzle, and turboprop, in which the main thrust is created by a propeller.

In 1909, the design of a turbojet engine was developed by engineer N. Gerasimov. In 1914, Lieutenant of the Russian Navy M.N. Nikolskoy designed and built a model of a turboprop aircraft engine. The gaseous combustion products of a mixture of turpentine and nitric acid served as the working fluid for driving the three-stage turbine. The turbine worked not only on the propeller: the exhaust gaseous products of combustion, directed to the tail (jet) nozzle, created jet thrust in addition to the thrust force of the propeller.

In 1924, V. I. Bazarov developed the design of an aircraft turbocompressor jet engine, which consisted of three elements: a combustion chamber, a gas turbine, and a compressor. For the first time, the compressed air flow here was divided into two branches: the smaller part went into the combustion chamber (to the burner), and the larger part was mixed with the working gases to lower their temperature in front of the turbine. This ensured the safety of the turbine blades. The power of the multistage turbine was used to drive the centrifugal compressor of the engine itself and partly to rotate the propeller. In addition to the propeller, thrust was created by the reaction of a jet of gases passed through the tail nozzle.

In 1939, the construction of turbojet engines designed by A. M. Lyulka began at the Kirov Plant in Leningrad. His trials were interrupted by the war.

In 1941, in England, the first flight was made on an experimental fighter aircraft equipped with a turbojet engine designed by F. Whittle. It was equipped with a gas turbine engine that drove a centrifugal compressor that supplied air to the combustion chamber. Combustion products were used to create jet thrust.

Whittle's Gloster aircraft (E.28/39)

In a turbojet engine, air entering during flight is compressed first in the air intake and then in the turbocharger. Compressed air is fed into the combustion chamber, where liquid fuel (most often aviation kerosene) is injected. Partial expansion of the gases formed during combustion occurs in the turbine that rotates the compressor, and the final expansion occurs in the jet nozzle. An afterburner can be installed between the turbine and the jet engine, designed for additional combustion of fuel.

Today, most military and civil aircraft, as well as some helicopters, are equipped with turbojet engines.

In a turboprop engine, the main thrust is created by a propeller, and an additional (about 10%) - by a jet of gases flowing from a jet nozzle. The principle of operation of a turboprop engine is similar to a turbojet engine, with the difference that the turbine rotates not only the compressor, but also the propeller. These engines are used in subsonic aircraft and helicopters, as well as for the movement of high-speed ships and cars.

The earliest solid propellant jet engines were used in combat missiles. Their widespread use began in the 19th century, when missile units appeared in many armies. At the end of the XIX century. the first smokeless powders were created, with more stable combustion and greater efficiency.

In the 1920s-1930s, work was underway to create jet weapons. This led to the appearance of rocket launchers - "Katyusha" in the Soviet Union, six-barreled rocket mortars in Germany.

Obtaining new types of gunpowder made it possible to use solid-propellant jet engines in combat missiles, including ballistic ones. In addition, they are used in aviation and astronautics as engines of the first stages of launch vehicles, starting engines for aircraft with ramjet engines and brake engines for spacecraft.

A solid propellant jet engine consists of a body (combustion chamber) in which the entire supply of fuel and a jet nozzle are located. The body is made of steel or fiberglass. Nozzle - made of graphite, refractory alloys, graphite.

The fuel is ignited by an igniter.

Thrust is controlled by changing the combustion surface of the charge or the area of ​​the critical section of the nozzle, as well as by injecting liquid into the combustion chamber.

The direction of thrust can be changed by gas rudders, a deflecting nozzle (deflector), auxiliary control engines, etc.

Jet solid propellant engines are very reliable, can be stored for a long time, and therefore, are constantly ready for launch.

JET ENGINE, an engine that creates the traction force necessary for movement by converting potential energy into kinetic energy of the jet stream of the working fluid. Under the working fluid m, in relation to engines, understand the substance (gas, liquid, solid), with the help of thermal energy, released during the combustion of fuel, is converted into useful mechanical work. As a result of the expiration of the working fluid from the engine nozzle, a reactive force is formed in the form of a reaction (recoil) of a jet directed in space in the direction opposite to the outflow of the jet. Various types of energy (chemical, nuclear, electrical, solar) can be converted into the kinetic (speed) energy of a jet stream in a jet engine.

A jet engine (direct reaction engine) combines the engine itself with a propeller, that is, it provides its own movement without the participation of intermediate mechanisms. To create jet thrust (engine thrust) used by a jet engine, you need: a source of initial (primary) energy, which is converted into the kinetic energy of the jet stream; the working fluid, which is ejected from the jet engine in the form of a jet stream; the jet engine itself is an energy converter. Engine thrust - this is a reactive force, which is the result of gas-dynamic forces of pressure and friction applied to the internal and external surfaces of the engine. Distinguish between internal thrust (reactive thrust) - the resultant of all gas-dynamic forces applied to the engine, without taking into account external resistance and effective thrust, taking into account the external resistance of the power plant. The initial energy is stored on board an aircraft or other apparatus equipped with a jet engine (chemical fuel, nuclear fuel), or (in principle) can come from outside (solar energy).

To obtain a working fluid in a jet engine, a substance taken from environment(for example, air or water); a substance located in the tanks of the apparatus or directly in the chamber of a jet engine; a mixture of substances coming from the environment and stored on board the apparatus. In modern jet engines, the most commonly used primary energy is chemical energy. In this case, the working fluid is incandescent gases - products of combustion chemical fuel. During the operation of a jet engine, the chemical energy of the burning substances is converted into thermal energy of combustion products, and the thermal energy of hot gases is converted into mechanical energy. forward movement jet stream and, consequently, the apparatus on which the engine is installed.

The principle of operation of a jet engine

In a jet engine (Fig. 1), a jet of air enters the engine, meets with turbines rotating at great speed compressor , which sucks in air from the external environment (using a built-in fan). Thus, two tasks are solved - the primary air intake and the cooling of the entire engine as a whole. Compressor turbine blades compress the air by about 30 times or more and "push" it (inject) into the combustion chamber (the working fluid is generated), which is the main part of any jet engine. The combustion chamber also acts as a carburetor, mixing fuel with air. This can be, for example, a mixture of air and kerosene, as in a turbojet engine of a modern jet aircraft, or a mixture of liquid oxygen and alcohol, as in some liquid rocket engines, or some kind of solid propellant for powder rockets. After the formation of the fuel-air mixture, it is ignited and energy is released in the form of heat, i.e., only such substances can serve as fuel for jet engines, which, when chemical reaction in the engine (combustion) they release a lot of heat, and also form a large number of gases.

In the process of ignition, there is a significant heating of the mixture and surrounding parts, as well as volumetric expansion. In fact, the jet engine uses a controlled explosion for propulsion. The combustion chamber of a jet engine is one of its hottest parts (the temperature in it reaches 2700 ° C), it must be constantly cooled intensively. The jet engine is equipped with a nozzle through which hot gases, the products of fuel combustion in the engine, flow out of the engine at great speed. In some engines, gases enter the nozzle immediately after the combustion chamber, for example, in rocket or ramjet engines. In turbojet engines, the gases after the combustion chamber first pass through turbine , which is given part of its thermal energy to drive a compressor that compresses air in front of the combustion chamber. But anyway, the nozzle is the last part of the engine - gases flow through it before leaving the engine. It forms a direct jet stream. The cold air forced by the compressor is directed into the nozzle to cool the internal parts of the engine. The jet nozzle may have various forms and design depending on the type of engine. If the outflow velocity must exceed the speed of sound, then the nozzle is given the shape of an expanding pipe, or first narrowing and then expanding (Laval nozzle). Only in a pipe of this shape can gas be accelerated to supersonic speeds, to step over the "sonic barrier".

Depending on whether or not the environment is used during the operation of a jet engine, they are divided into two main classes - jet engines(WFD) and rocket engines(RD). All WFD - heat engines, the working fluid of which is formed during the oxidation reaction of a combustible substance with atmospheric oxygen. The air coming from the atmosphere makes up the bulk of the working fluid of the WFD. Thus, an apparatus with a WFD carries a source of energy (fuel) on board, and draws most of the working fluid from the environment. These include turbojet engine (TRD), ramjet engine (ramjet), pulsed jet engine (PuVRD), hypersonic ramjet engine (scramjet). Unlike the WFD, all components of the working fluid of the RD are on board the vehicle equipped with the RD. The absence of a propeller interacting with the environment and the presence of all components of the working fluid on board the vehicle make the RD suitable for space operation. There are also combined rocket engines, which are, as it were, a combination of both main types.

Main characteristics of jet engines

Main technical parameter characterizing a jet engine is thrust - the force that the engine develops in the direction of movement of the device, specific impulse - the ratio of engine thrust to the mass of rocket fuel (working fluid) consumed in 1 s, or an identical characteristic - specific fuel consumption (the amount of fuel consumed for 1 s per 1 N of the thrust developed by the jet engine), the specific mass of the engine (the mass of the jet engine in working condition per unit of thrust developed by it). For many types of jet engines important characteristics are dimensions and resource. Specific impulse is an indicator of the degree of perfection or quality of the engine. The above diagram (Fig. 2) graphically presents the upper values ​​of this indicator for different types of jet engines, depending on the flight speed, expressed in the form of a Mach number, which allows you to see the scope of each type of engine. This indicator is also a measure of the efficiency of the engine.

Thrust - the force with which a jet engine acts on a device equipped with this engine - is determined by the formula: $$P = mW_c + F_c (p_c - p_n),$$ where $m$ is the mass flow rate (mass flow rate) of the working fluid for 1 s; $W_c$ is the speed of the working fluid in the nozzle section; $F_c$ is the area of ​​the outlet section of the nozzle; $p_c$ – gas pressure in the nozzle section; $p_n$ – ambient pressure (usually Atmosphere pressure). As can be seen from the formula, the thrust of a jet engine depends on the ambient pressure. It is greatest in emptiness and least of all in the densest layers of the atmosphere, i.e., it varies depending on the flight altitude of an apparatus equipped with a jet engine above sea level, if flight in the Earth’s atmosphere is considered. The specific impulse of a jet engine is directly proportional to the speed of the outflow of the working fluid from the nozzle. The outflow rate increases with an increase in the temperature of the outflowing working fluid and a decrease in the molecular weight of the fuel (the less molecular mass fuel, the greater the volume of gases formed during its combustion, and, consequently, the rate of their expiration). Since the rate of exhaust of combustion products (working fluid) is determined by physical and chemical properties components of the fuel and the design features of the engine, being a constant value with not very large changes in the operating mode of the jet engine, then the magnitude of the reactive force is determined mainly by the mass second fuel consumption and varies over a very wide range (minimum for electric ones - maximum for liquid and solid propellant rocket engines) . Small thrust jet engines are mainly used in stabilization and control systems. aircraft. In space, where gravitational forces are felt weakly and there is practically no medium, the resistance of which would have to be overcome, they can also be used for overclocking. RD with maximum thrust is necessary for launching rockets at long ranges and altitudes, and especially for launching aircraft into space, i.e., for accelerating them to first space velocity. Such engines consume a very large amount of fuel; they usually work for a very short time, accelerating the rockets to a given speed.

WFDs use ambient air as the main component of the working fluid, which is much more economical. WJDs can operate continuously for many hours, making them suitable for aviation use. Different schemes allowed them to be used for aircraft operated in different flight modes. Turbojet engines (TRDs) are widely used, which are installed on almost all modern aircraft without exception. Like all engines that use atmospheric air, turbojet engines need a special device to compress the air before it enters the combustion chamber. In a turbojet engine, a compressor is used to compress the air, and the design of the engine largely depends on the type of compressor. Uncompressor jet engines are much simpler in design, in which the necessary pressure increase is carried out in other ways; these are pulsating and direct-flow motors. In a pulsating jet engine (PUVRD), this is usually done by a valve grill installed at the engine inlet, when a new portion of the fuel-air mixture fills the combustion chamber and a flash occurs in it, the valves close, isolating the combustion chamber from the engine inlet. As a result, the pressure in the chamber rises, and the gases rush out through the jet nozzle, after which the whole process is repeated. In a compressorless engine of another type, a ramjet, there is not even this valve grid and atmospheric air, entering the engine inlet at a speed equal speed flight, is compressed due to the velocity pressure and enters the combustion chamber. The injected fuel burns, the heat content of the flow increases, which flows out through the jet nozzle at a speed greater than the flight speed. Due to this, the jet thrust of the ramjet is created. The main disadvantage of the ramjet is the inability to independently provide takeoff and acceleration of the aircraft (LA). It is required first to accelerate the aircraft to a speed at which the ramjet is launched and its stable operation is ensured. The peculiarity of the aerodynamic scheme of supersonic aircraft with ramjet engines (ramjet engines) is due to the presence of special accelerating engines that provide the speed necessary to start stable operation of the ramjet. This makes the tail part of the structure heavier and requires the installation of stabilizers to ensure the necessary stability.

History reference

The principle of jet propulsion has been known for a long time. Heron's ball can be considered the ancestor of the jet engine. Solid rocket motors(RDTT - solid fuel rocket engine) - powder rockets appeared in China in the 10th century. n. e. For hundreds of years, such missiles were used first in the East, and then in Europe as fireworks, signal, combat. An important stage in the development of the idea of ​​jet propulsion was the idea of ​​using a rocket as an engine for an aircraft. It was first formulated by the Russian revolutionary Narodnaya Volya N. I. Kibalchich, who in March 1881, shortly before his execution, proposed a scheme for an aircraft (rocket plane) using jet propulsion from explosive powder gases. Solid propellant rocket engines are used in all classes of military missiles (ballistic, anti-aircraft, anti-tank, etc.), in space (for example, as starting and sustainer engines) and aviation technology(aircraft takeoff accelerators, in systems ejection), etc. Small solid propellant engines are used as boosters for aircraft takeoff. Electric rocket engines and nuclear rocket engines can be used in spacecraft.

Turbojet engines and dual-circuit turbojet engines are equipped with most military and civil aircraft around the world, they are used in helicopters. These jet engines are suitable for flights at both subsonic and supersonic speeds; they are also installed on projectile aircraft, supersonic turbojet engines can be used in the first stages aerospace aircraft, rocket and space technology, etc.

Great importance to create jet engines had the theoretical work of Russian scientists S. S. Nezhdanovsky, I. V. Meshchersky, N. E. Zhukovsky, the works of the French scientist R. Enot-Peltri, the German scientist G. Oberth. An important contribution to the creation of the VRD was the work of the Soviet scientist B. S. Stechkin, The Theory of an Air Jet Engine, published in 1929. Practically more than 99% of aircraft use a jet engine to one degree or another.