Engine overview. railway and rdt. Why do Americans fight among themselves over Russian engines? Liquid rocket engine fuel

Design solid fuel engine(TTRD) is simple; it consists of a housing (combustion chamber) and a jet nozzle. The combustion chamber is the main load-bearing element of the engine and the rocket as a whole. The material for its manufacture is steel or plastic. Nozzle designed to accelerate gases to a certain speed and give the flow the required direction. It is a closed channel with a special profile. The housing contains fuel. The engine housing is usually made of steel, sometimes of fiberglass. The part of the nozzle that experiences the greatest stress is made of graphite, refractory metals and their alloys, the rest is made of steel, plastics, and graphite.

When the gas produced by the combustion of fuel passes through the nozzle, it is expelled at a speed that can be greater than the speed of sound. As a result, a recoil force appears, the direction of which is opposite to the outflow of the gas stream. This force is called reactive, or just traction. The housing and nozzle of operating engines must be protected from burnout; for this purpose, heat-insulating and heat-resistant materials are used.

Compared to other types of rocket engines, a turbojet engine is quite simply designed, but has reduced thrust, short operating time and difficulty in control. Therefore, being quite reliable, it is used mainly to create thrust during “auxiliary” operations and in the engines of intercontinental ballistic missiles.

Until now, turbojet engines have rarely been used on board spacecraft. One of the reasons for this is the excessive acceleration that is imparted to the design and equipment of the rocket during operation of the solid propellant engine. And to launch a rocket, it is necessary that the engine develop a small amount of thrust over a long period of time.

Solid propellant engines allowed the United States to launch its first artificial satellite in 1958, following the USSR, and put the spacecraft on a flight path to other planets in 1959. To date, the most powerful space turbojet engine, the DM-2, has been created in the United States, capable of developing a thrust of 1634 tons.

Prospects for the development of solid fuel space engines are:

• improvement of engine manufacturing technologies;
• development of jet nozzles that can operate for a longer time;
• use of modern materials;
• improvement of mixed fuel compositions, etc.

Solid propellant rocket engine (SRF)- an engine running on solid fuel is most often used in rocket artillery and much less often in astronautics; is the oldest of the heat engines.

The fuel used in such engines is a solid substance (a mixture of individual substances) that can burn without oxygen, releasing a large amount of hot gases that are used to create jet thrust.

There are two classes of rocket fuel: dual-base propellants and blended propellants.

Dual fuels- are solid solutions in a non-volatile solvent (most often nitrocellulose in nitroglycerin). Advantages - good mechanical, temperature and other structural characteristics, retain their properties during long-term storage, simple and cheap to manufacture, environmentally friendly (there are no harmful substances during combustion). The disadvantage is the relatively low power and increased sensitivity to shock. Charges made from this fuel are most often used in small corrective engines.

Blended fuels- modern mixtures consist of ammonium perchlorate (as an oxidizing agent), aluminum in powder form and an organic polymer to bind the mixture. Aluminum and polymer play the role of fuel, with the metal being the main source of energy and the polymer being the main source of gaseous products. They are characterized by insensitivity to impacts, high combustion intensity at low pressures and are very difficult to extinguish.

Fuel in the form of fuel charges is placed in the combustion chamber. After the start, combustion continues until the fuel is completely burned out; thrust changes according to laws determined by fuel combustion and is practically not regulated. Thrust variation is achieved by using fuel with different combustion rates and selecting a suitable charge configuration.

With the help of an igniter, the fuel components are heated, a chemical oxidation-reduction reaction begins between them, and the fuel gradually burns. This produces a gas with high pressure and temperature. The pressure of hot gases with the help of a nozzle is converted into jet thrust, which in its magnitude is proportional to the mass of combustion products and the speed of their departure from the engine nozzle.

Despite its simplicity, accurate calculation of turbojet engine operating parameters is a complex task.

Solid propellant engines have a number of advantages over liquid rocket engines: the engine is quite simple to manufacture, can be stored for a long time while maintaining its characteristics, and is relatively explosion-proof. However, in terms of power, they are inferior to liquid engines by about 10–30%, have difficulties in regulating power and have a large mass of the engine as a whole.

In some cases, a type of turbojet engine is used, in which one component of the fuel is in a solid state, and the second (most often an oxidizer) is in a liquid state.

A liquid rocket engine is an engine that uses liquefied gases and chemical liquids as fuel. Depending on the number of components, liquid rocket engines are divided into one-, two- and three-component ones.

Brief history of development

For the first time, the use of liquefied hydrogen and oxygen as fuel for rockets was proposed by K.E. Tsiolkovsky in 1903. The first prototype of a liquid-propellant rocket engine was created by the American Robert Howard in 1926. Subsequently, similar developments were carried out in the USSR, USA, and Germany. The greatest successes were achieved by German scientists: Thiel, Walter, von Braun. During World War II they created a whole line of rocket engines for military purposes. There is an opinion that if the Reich had created the V-2 earlier, they would have won the war. Subsequently, the Cold War and the arms race became a catalyst for accelerating the development of liquid propellant rocket engines for use in the space program. With the help of RD-108, the first artificial Earth satellites were launched into orbit.

Today, liquid-propellant rocket engines are used in space programs and heavy missile weapons.

Scope of application

As mentioned above, liquid-propellant rocket engines are used mainly as engines for spacecraft and launch vehicles. The main advantages of liquid propellant engines are:

• highest specific impulse in class;
• the ability to perform a full stop and restart paired with traction control gives increased maneuverability;
• significantly lower weight of the fuel compartment compared to solid fuel engines.

Among the disadvantages of liquid rocket engines:

• more complex device and high cost;
• increased requirements for safe transportation;
• In a state of weightlessness, it is necessary to use additional engines to settle the fuel.

However, the main disadvantage of liquid propellant engines is the limit of the energy capabilities of the fuel, which limits space exploration with their help to the distance of Venus and Mars.

Device and principle of operation

The principle of operation of a liquid propellant rocket engine is the same, but it is achieved using different device circuits. Using pumps, fuel and oxidizer are supplied from different tanks to the nozzle head, pumped into the combustion chamber and mixed. After combustion under pressure, the internal energy of the fuel turns into kinetic energy and flows out through the nozzle, creating jet thrust.

The fuel system consists of fuel tanks, pipelines and pumps with a turbine for pumping fuel from the tank into the pipeline and a control valve.

Pumping fuel supply creates high pressure in the chamber and, as a result, greater expansion of the working fluid, due to which the maximum value of the specific impulse is achieved.

Injector head - a block of injectors for injecting fuel components into the combustion chamber. The main requirement for an injector is high-quality mixing and speed of fuel supply into the combustion chamber.

Cooling system

Although the proportion of heat transfer from the structure during the combustion process is insignificant, the cooling problem is relevant due to the high combustion temperature (>3000 K) and threatens thermal destruction of the engine. There are several types of chamber wall cooling:

Regenerative cooling is based on creating a cavity in the walls of the chamber through which fuel passes without an oxidizer, cooling the chamber wall, and the heat, together with the coolant (fuel), is returned back to the chamber.

The wall layer is a layer of gas created from fuel vapors near the walls of the chamber. This effect is achieved by installing nozzles around the periphery of the head that supply only fuel. Thus, the combustible mixture lacks an oxidizer, and combustion at the wall does not occur as intensely as in the center of the chamber. The wall layer temperature insulates the high temperatures in the center of the chamber from the walls of the combustion chamber.

The ablative method of cooling a liquid rocket engine is carried out by applying a special heat-protective coating to the walls of the chamber and nozzles. At high temperatures, the coating changes from a solid to a gaseous state, absorbing a large proportion of heat. This method of cooling a liquid rocket engine was used in the Apollo lunar program.

Launching a liquid-propellant rocket engine is a very important operation in terms of explosion hazard in the event of failures in its implementation. There are self-igniting components with which there are no difficulties, but when using an external initiator for ignition, perfect coordination of its supply with the fuel components is necessary. The accumulation of unburnt fuel in the chamber has destructive explosive force and promises serious consequences.

The launch of large liquid-propellant rocket engines takes place in several stages, followed by reaching maximum power, while small engines are launched with immediate access to one hundred percent power.

The automatic control system for liquid-propellant rocket engines is characterized by the safe start of the engine and entry to the main mode, control of stable operation, adjustment of thrust according to the flight plan, adjustment of consumables, and shutdown when reaching a given trajectory. Due to factors that cannot be calculated, the liquid-propellant rocket engine is equipped with a guaranteed supply of fuel so that the rocket can enter a given orbit in the event of deviations in the program.

Propellant components and their selection during the design process are critical to the design of a liquid propellant rocket engine. Based on this, the conditions of storage, transportation and production technology are determined. The most important indicator of the combination of components is the specific impulse, on which the distribution of the percentage of fuel and cargo mass depends. The dimensions and mass of the rocket are calculated using the Tsiolkovsky formula. In addition to the specific impulse, density affects the size of tanks with fuel components, the boiling point can limit the operating conditions of rockets, chemical aggressiveness is characteristic of all oxidizers and, if the tanks are not operated in accordance with the rules, can cause a tank fire, the toxicity of some fuel compounds can cause serious harm to the atmosphere and the environment . Therefore, although fluorine is a better oxidizing agent than oxygen, it is not used due to its toxicity.

Single-component liquid rocket engines use liquid as fuel, which, interacting with a catalyst, disintegrates with the release of hot gas. The main advantage of single-propellant rocket engines is the simplicity of their design, and although the specific impulse of such engines is small, they are ideal as low-thrust engines for orientation and stabilization of spacecraft. These engines use a displacement fuel supply system and, due to the low process temperature, do not require a cooling system. Single-component engines also include gas-jet engines, which are used in conditions where thermal and chemical emissions are inadmissible.

In the early 70s, the USA and the USSR were developing three-component liquid rocket engines that would use hydrogen and hydrocarbon fuel as fuel. This way the engine would run on kerosene and oxygen at startup and switch to liquid hydrogen and oxygen at high altitude. An example of a three-component liquid propellant engine in Russia is the RD-701.

Rocket control was first used in V-2 rockets using graphite gas-dynamic rudders, but this reduced engine thrust, and modern rockets use rotating cameras attached to the body with hinges, creating maneuverability in one or two planes. In addition to rotating cameras, control motors are also used, which are fixed with nozzles in the opposite direction and are turned on when it is necessary to control the device in space.

A closed-cycle liquid-propellant rocket engine is an engine in which one of the components is gasified when burned at a low temperature with a small part of the other component; the resulting gas acts as the working fluid of the turbine, and is then fed into the combustion chamber, where it burns with the remainder of the fuel components and creates jet thrust. The main disadvantage of this scheme is the complexity of the design, but at the same time the specific impulse increases.

The prospect of increasing the power of liquid rocket engines

In the Russian school of liquid propellant rocket engine creators, the leader of which was Academician Glushko for a long time, they strive for the maximum use of fuel energy and, as a consequence, the maximum possible specific impulse. Since the maximum specific impulse can be obtained only by increasing the expansion of the combustion products in the nozzle, all developments are being carried out in search of an ideal fuel mixture.

The recent accident of the Dnepr rocket, a space launch vehicle converted from the R-36M UTTH military rocket, has again sparked interest in rocket fuel.

V-2 (“V-2”) formed the basis of all post-war rocket technology, both American and Soviet

The launch of 900 V-2 rockets required 12 thousand tons of liquid oxygen, 4 thousand tons of ethyl alcohol, 2 thousand tons of methanol, 500 tons of hydrogen peroxide and 1.5 thousand tons of explosives

Instead of alcohol, which Wernher von Braun used along with liquid oxygen, Korolev chose kerosene for his first rockets

Neither gasoline, kerosene, nor diesel fuel ignite themselves when interacting with acid, and for military missiles, self-ignition is one of the key fuel requirements

The S-4B rocket, the third stage of another brainchild of Wernher von Braun - the most powerful American launch vehicle Saturn V. The latter has 13 successful launches (from 1967 to 1973). It was with her help that man stepped on the moon

Liquid rocket engines (LPRE) are very advanced machines, and their characteristics are determined by 90%, or even more, by the fuel used. The efficiency of the fuel depends on the composition and stored energy. An ideal fuel should consist of light elements - from the very beginning of the periodic table, which provide maximum energy during oxidation. But these are not all the requirements for fuel - it must also be compatible with construction materials, stable during storage and, if possible, inexpensive. But a rocket is not only an engine, but also tanks of limited volume: in order to take more fuel on board, its density must be higher. In addition to fuel, the rocket also carries an oxidizer.

The ideal oxidizing agent from a chemical point of view is liquid oxygen. But a rocket is not limited to chemistry alone; it is a design in which everything is interconnected. Wernher von Braun chose alcohol and liquid oxygen for the V-2, and the rocket had a range of 270 km. But if its engine ran on nitric acid and diesel fuel, then the range would increase by a quarter, because two tons more of such fuel fit into the same tanks!

Rocket fuel is a storehouse of chemical energy in a compact form. The more energy it stores, the better the fuel. Therefore, substances that are good for rocket fuel are always extremely chemically active, constantly trying to release hidden energy, corroding, burning and destroying everything around them. All rocket oxidizers are either explosive, poisonous, or unstable. Liquid oxygen is the only exception, and only because nature has become accustomed to 20% free oxygen in the atmosphere. But even liquid oxygen requires respect.

Keep forever

The R-1, R-2 and R-5 ballistic missiles, created under the leadership of Sergei Korolev, not only showed the promise of this type of weapon, but also made it clear that liquid oxygen is not very suitable for combat missiles. Despite the fact that the R-5M was the first missile with a nuclear warhead, and in 1955 there was even a real test with the detonation of a nuclear charge, the military was not satisfied that the missile had to be refueled immediately before launch. A replacement for liquid oxygen was required, a complete replacement, such that it would not freeze in the Siberian frosts and would not boil away in the Karakum heat: that is, with a temperature range from -55 degrees to +55 degrees Celsius. True, no problems were expected with boiling in the tanks, since the pressure in the tank is increased, and with increased pressure the boiling point is higher. But oxygen will not be liquid at any pressure at a temperature above critical, that is -113 degrees Celsius. And such frosts don’t even happen in Antarctica.

Nitric acid HNO3 is another obvious oxidizing agent for liquid propellant engines, and its use in rocketry has paralleled that of liquid oxygen. Salts of nitric acid - nitrates, especially potassium nitrate - have been used for many centuries as an oxidizing agent for the very first rocket fuel - black powder.

A molecule of nitric acid contains, as ballast, only one nitrogen atom and “half” a water molecule, and two and a half oxygen atoms can be used to oxidize fuel. But nitric acid is a very “cunning” substance, so strange that it continuously reacts with itself - hydrogen atoms from one molecule of acid are split off and attached to neighboring ones, forming fragile, but extremely chemically active aggregates. Because of this, various types of impurities are necessarily formed in nitric acid.

In addition, nitric acid obviously does not meet the requirements of compatibility with structural materials—it is necessary to specifically select metal for tanks, pipes, and liquid-propellant rocket engine chambers. Nevertheless, “nitrogen” became a popular oxidizer back in the 1930s - it is cheap, produced in large quantities, stable enough to cool the engine chamber, and is fire and explosion proof. Its density is noticeably greater than that of liquid oxygen, but its main advantage compared to liquid oxygen is that it does not boil away, does not require thermal insulation, and can be stored indefinitely in a suitable container. But where can I get it, a suitable container?

The entire 1930s and 1940s were spent searching for suitable containers for nitric acid. But even the most resistant grades of stainless steel were slowly destroyed by concentrated nitrogen, resulting in the formation of a thick greenish “jelly” at the bottom of the tank, a mixture of metal salts, which, of course, cannot be fed into a rocket engine - it will instantly clog and explode.

To reduce the corrosive activity of nitric acid, various substances began to be added to it, trying, often through trial and error, to find a combination that, on the one hand, would not spoil the oxidizer, and on the other, would make it more convenient to use. But a successful additive was found only in the late 1950s by American chemists - it turned out that just 0.5% hydrofluoric acid reduces the corrosion rate of stainless steel tenfold! Soviet chemists were ten to fifteen years late with this discovery.

Secret additives

Nevertheless, the first missile interceptor aircraft in the USSR, BI-1, used nitric acid and kerosene. The tanks and pipes had to be made of Monel metal, an alloy of nickel and copper. This alloy was obtained “naturally” from certain polymetallic ores, and therefore was a popular construction material in the second third of the twentieth century. Its appearance can be judged by the metal rubles - they are made of an almost “rocket” alloy. During the war, however, there was a shortage not only of copper and nickel, but also of stainless steel. I had to use a regular one, coated with chrome for protection. But the thin layer was quickly eaten away by acid, so after each engine start, the remaining fuel mixture had to be removed from the combustion chamber with scrapers - the technicians inevitably inhaled toxic fumes. One of the pioneers of rocketry, Boris Chertok, once almost died when an engine for BI-1 exploded on a test bench; he described this episode in his wonderful book “Rockets and People.”

In addition to additives that reduce the aggressiveness of nitric acid, they tried to add various substances to it in order to increase its effectiveness as an oxidizing agent. The most effective substance was nitrogen dioxide, another "strange" compound. Usually it is a brown gas with a sharp, unpleasant odor, but as soon as it is slightly cooled, it liquefies and two molecules of dioxide stick together into one. Therefore, the compound is often called nitrogen tetroxide, or nitrogen tetroxide - AT. At atmospheric pressure, AT boils at room temperature (+21 degrees), and freezes at -11 degrees. The closer to the freezing point, the paler the color of the compound, eventually becoming pale yellow, and in the solid state - almost colorless. This is because the gas consists mainly of NO2 molecules, the liquid consists of a mixture of NO2 and N2O4 dimers, and in the solid only colorless dimers remain.

The addition of AT to nitric acid increases the efficiency of the oxidizer for many reasons at once - AT contains less “ballast”, binds water entering the oxidizer, which reduces the corrosive activity of the acid. The most interesting thing is that with the dissolution of AT in AA, the density of the solution first increases and reaches a maximum at 14% dissolved AT. It was this version of the composition that American rocket scientists chose for their combat missiles. Ours sought to improve engine performance at any cost, so the AK-20 and AK-27 oxidizers contained 20% and 27%, respectively, of dissolved nitrogen tetroxide. The first oxidizer was used in anti-aircraft missiles, and the second in ballistic missiles. Yangel Design Bureau created the R-12 medium-range missile, which used the AK-27 and a special grade of kerosene TM-185.

Lighters

In parallel with the search for the best oxidizer, there was a search for the optimal fuel. The military would be most satisfied with the product of petroleum distillation, but other substances, if they were produced in sufficient quantities and were inexpensive, could also be used. There was only one problem - neither gasoline, nor kerosene, nor diesel fuel ignite on their own when in contact with nitric acid, and for military missiles, self-ignition is one of the key requirements for fuel. Although our first intercontinental rocket, the R-7, used a kerosene-liquid oxygen pair, it became clear that pyrotechnic ignition was inconvenient for combat rockets. When preparing the rocket for launch, it was necessary to manually insert into each nozzle (and the R-7 has no less than 32-20 main chambers and 12 steering ones) a wooden cross with an incendiary bomb, connect all the electrical wires that ignite the bombs, and do many other things preparatory operations.

In the R-12, these shortcomings were taken into account, and ignition was provided by starting fuel, which self-ignited upon contact with nitric acid. Its composition was discovered by German rocket scientists during World War II, and it was called Tonka-250. Our rocket scientists renamed it in accordance with GOSTs as TG-02. Now the rocket could sit fueled for several weeks, and this was a great success, since it could be launched within a couple of hours instead of three days for the R-7. But three components is a lot for a combat missile, and for use as the main fuel, the TG-02 was only suitable for anti-aircraft missiles; for long-range ballistic missiles, something more effective was needed.

Hypergolics

Chemists called pairs of substances that spontaneously ignite on contact “hypergolic,” that is, roughly translated from Greek, having excessive affinity for each other. They knew that substances containing nitrogen, in addition to carbon and hydrogen, ignite best with nitric acid. But “better” – how much?

Autoignition delay is a key property for the chemical vapors we want to burn in a rocket engine. Imagine - the supply is turned on, fuel and oxidizer accumulate in the chamber, but there is no ignition! But when it finally happens, a powerful explosion blows the rocket engine chamber into pieces. To determine the self-ignition delay, different researchers built stands of varying complexity - from two pipettes, synchronously squeezing out a drop of oxidizer and fuel, to small rocket engines without a nozzle - an injector head and a short cylindrical pipe. All the same, explosions were heard very often, getting on the nerves, knocking out windows and damaging sensors.

Very quickly the “ideal hypergol” was discovered - hydrazine, an old friend of chemists. This substance, which has the formula N2H4, is very similar in physical properties to water - the density is several percent higher, the freezing point is +1.5 degrees, the boiling point is +113 degrees, viscosity and everything else is like water, but the smell...

Hydrazine was first obtained in pure form at the end of the 19th century, and was first used in rocket fuel by the Germans in 1933, but as a relatively small additive for self-ignition. As an independent fuel, hydrazine was expensive, its production was insufficient, but, most importantly, the military was not satisfied with its freezing temperature - higher than that of water! What was needed was “hydrazine antifreeze,” and the search for it was ongoing. Hydrazine is really good! For the launch of the first US satellite, Explorer, Wernher von Braun replaced the alcohol in the Redstone rocket with Hydyne, a mixture of 60% hydrazine and 40% alcohol. This fuel improved the energy efficiency of the first stage, but to achieve the required characteristics it was necessary to lengthen the tanks.

Hydrazine, like ammonia NH3, consists only of nitrogen and hydrogen. But if energy is released during the formation of ammonia from elements, then during the formation of hydrazine energy is absorbed - this is why direct synthesis of hydrazine is impossible. But the energy absorbed during formation will then be released during the combustion of hydrazine in a liquid-propellant rocket engine and will be used to increase the specific impulse - the main indicator of engine perfection. The oxygen-kerosene pair allows you to obtain a specific thrust for the first stage engines in the region of 300 seconds. Replacing liquid oxygen with nitric acid worsens this value to 220 seconds. Such deterioration requires almost doubling the starting mass. If you replace kerosene with hydrazine, most of this deterioration can be reversed. But the military needed the fuel to not freeze, and they demanded an alternative.

The paths diverged

And here the paths of our and American chemists diverged! In the USSR, chemists came up with a method for producing unsymmetrical dimethylhydrazine, while the Americans preferred a simpler process in which monomethylhydrazine was obtained. Both of these liquids, despite their extreme toxicity, suited both the designers and the military. The rocket scientists were no strangers to being careful when handling hazardous substances, but the new substances were still so toxic that an ordinary gas mask could not cope with clearing their vapors from the air! It was necessary to either use an insulating gas mask or a special cartridge that oxidized toxic fumes to a safe state. But methylated hydrazine derivatives were less explosive, absorbed less water vapor, and were thermally more stable. But the boiling point and density decreased compared to hydrazine.

Therefore, the search continued. At one time, the Americans very widely used Aerosin-50, a mixture of hydrazine and UDMH, which was a consequence of the invention of a technological process in which they were produced simultaneously. Later, this method was supplanted by more advanced ones, but Aerozin-50 managed to spread, and both the Titan-2 ballistic missiles and the Apollo spacecraft flew on it. The Saturn V rocket propelled it toward the Moon on liquid hydrogen and oxygen, but Apollo's own engine, which had to be fired several times during the week-long flight, had to use a self-igniting, long-lasting fuel.

Greenhouse conditions

But then an amazing metamorphosis occurred with ballistic missiles - they hid in silos to protect them from the enemy’s first strike. At the same time, frost resistance was no longer required, since the air in the mine was heated in winter and cooled in summer! Fuel could be selected without taking into account its frost resistance. And engine engineers immediately abandoned nitric acid, switching to pure nitrogen tetroxide. The one that boils at room temperature! After all, the pressure in the tank is increased, and at increased pressure the boiling point worries us much less. But now the corrosion of tanks and pipelines has decreased so much that it has become possible to keep the missile fueled throughout the entire period of combat duty! The first rocket that could stand fueled for 10 years in a row was the UR-100 designed by the Chelomey Design Bureau. Almost simultaneously with it, the much heavier R-36 from Yangel appeared. Its current descendant, the latest modification of the R-36M2, except for the tanks, has little in common with the original missile.

In terms of energy characteristics, the pairs “oxygen - kerosene” and “nitrogen tetroxide - UDMH” are very close. But the first pair is good for space launch vehicles, and the second is good for silo-based ICBMs. To work with such toxic substances, a special technology was developed - ampulization of the rocket after refueling. Its meaning is clear from the name: all highways are irreversibly blocked in order to avoid even the slightest leaks. It was first used on missiles for submarines, which also used such fuel.

Solid fuel

American rocket scientists preferred solid fuel for combat missiles. It had slightly worse characteristics, but the rocket required much less preparatory operations during launch. Ours also tried to use solid-fuel rockets, but the last stage still had to be made liquid in order to compensate for the variation in the operation of solid-fuel engines, which cannot be adjusted in the same way as liquid ones. And later, when missiles with multiple warheads appeared, the last liquid stage was tasked with “separating” them into targets. So the AT-UDMH pair was not left without work. It doesn’t remain even now: the engines of the Soyuz spacecraft, the International Space Station and many other devices run on this fuel.

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Rocket fuel (RT)

A substance or a set of substances that is a source of energy and working fluid to create reactive force in a rocket engine (RE). Based on the type of energy source, a distinction is made between chemical and nuclear RTs. The greatest practical application for the RDs of intercontinental ballistic missiles (ICBMs) used in the Strategic Missile Forces are chemical rocket launchers, which are both a source of energy released due to exothermic combustion reactions and a source of working fluid, which is the products of fuel combustion. Chemical RTs according to their state of aggregation are divided into liquid (LRT), solid (SRT) and mixed aggregate composition.

LRT - rocket fuels that are in a liquid aggregate state under operating conditions. Liquid fuels are divided into single-component (unitary) and two-component fuels, also called separate-feed fuels. Chemical substances or their mixtures that, under certain conditions, are capable of chemical decomposition or combustion reactions with the release of thermal energy can be considered as single-component liquid fuels. Such substances include, for example, hydrazine N2H4, hydrogen peroxide H2O2, ethylene oxide CH2CH2O, etc. Single-component liquid propellant rocket engines are used in low-thrust liquid propellant rocket engines, as fuel for rocket propellant control and orientation systems, as well as for gas-generating systems. Two-component liquid propellants consist of an oxidizer and a fuel. Substances containing predominantly atoms of oxidizing elements are used as oxidizing agents. These substances include liquid fluorine F2 and oxygen O2, concentrated nitric acid HNO3, nitric tetroxide N2O4. The most effective flammable liquid fuels are liquid hydrogen H2, kerosene T-1 (fraction with a boiling point of 150...280°C), hydrazine N2H4, unsymmetrical dimethylhydrazine H2NN(CH3)2 (UDMH). The metals Mg, Al and their hydrides, introduced into the composition of liquid fuels in the form of dispersed powders with the formation of gels, can also be used as fuels. When fed into the combustion chamber of RD, the components of the liquid propellant can spontaneously ignite (for example, N2O4 + H2NN(CH3)2) or not spontaneously ignite (liquid H2 + liquid O2). In the latter case, special ignition systems or special starting fuels are used. Two-component liquid propellant rockets are used primarily in propulsion engines of rockets and their stages. To impart a complex of required properties to liquid fuel components, special additives are usually introduced, which contribute, for example, to increasing the stability of the physical and chemical properties of the components during storage or operation. The main advantage of LRT, which determines the feasibility of their use, is the possibility of obtaining a high level of energy characteristics.

For example, for fuel based on liquid O2 and H2 at p/pa = 7/0.1 MPa, a specific impulse of up to 3835 m/s is realized, while for the most high-energy solid fuels its value does not exceed 3000 m/s under comparable conditions.

LRT components are divided into high-boiling and low-boiling. A high-boiling component is a component of liquid fuel that has a boiling point above 298K under standard conditions. High-boiling components in the operating temperature range are liquids. High-boiling components include nitric acid oxidizers, nitrogen tetroxide, as well as a number of widely used fuels - T-1 kerosene, unsymmetrical dimethylhydrazine, etc.

A low-boiling component is a component of liquid fuel that has a boiling point below 298K under standard conditions. In the temperature range of rocket technology operation, low-boiling components are usually in a gaseous state. To keep low-boiling components in a liquid state, special technological equipment is used. Among the low-boiling components, so-called cryogenic components are distinguished, having a boiling point below 120K. Cryogenic components include liquefied gases: oxygen, hydrogen, fluorine, etc. To reduce evaporation losses and increase density, it is possible to use a cryogenic component in a slurry state, in the form of a mixture of solid and liquid phases of this component.

TRT - homogeneous or heterogeneous explosive systems capable of self-combustion in a wide range of pressures (0.1...100 MPa) with the release of a significant amount of heat and gaseous combustion products. Based on their chemical composition and production method, they are divided into ballistic and mixed. The structural and energetic basis of ballistites are cellulose nitrates - colloxylins with a nitrogen content of about 12%, plasticized with low-volatile active solvents (nitroglycerin, dinitrate diethylene glycol) or other liquid nitroethers. Ballistites can contain powerful explosives (HMX) - octogen or hexogen, and also include chemical resistance stabilizers, combustion stabilizers, combustion modifiers, technological and energy additives (Al, Mg powders or their alloys). Ballistites are solid solutions located in the operating temperature range in a glassy physical state.

Mixed TRTs are heterogeneous mixtures of an oxidizer (mainly ammonium perchlorate NH4ClO4, potassium perchlorate KClO4 or ammonium nitrate NH4NO3) and a combustible binder, which is a plasticized polymer (for example, butyl rubber, polybutadiene, polyurethane) with the ingredients of the curing system, technological and special additives. In order to improve their energy characteristics, mixed TRTs can contain powerful high explosives (RDX or HMX) in amounts of up to 50% and up to 20% of metal combustibles (Al, Mg or their hydrides). Regulation of ballistic characteristics (burning rate and its dependence on various factors) of TRT is usually carried out by changing the dispersion of powder components or by introducing combustion modifiers into the fuel composition. The components of mixed TRT usually perform several functions: oxidizers are fillers of the polymer matrix and provide the required level of ballistic and energy-mass characteristics; combustibles, which in most cases are plasticized polymers, ensure the solidity of the solid propellant charge and the required level of its mechanical characteristics; metal fuel is designed to increase the density of the fuel and increase its energy capabilities.

A quantity of solid propellant determined by mass, which is the main source of energy and working fluid, having a given shape, size and initial combustion surface is called a solid fuel charge (SFC). In relation to solid propellant motors, solid propellant motors are understood as the part of the propellant rocket motor that ensures the required law of gas formation of the working fluid. According to the method of installation in the solid propellant rocket motor, charges are divided into inserted, firmly fastened, cast into the body and cast into the body, secured with cuffs.

In the operating temperature range, mixed TRTs are in a highly elastic state. TRTs are easier to operate than LRTs, but have inferior energy characteristics.

Fuels of mixed aggregate composition (hybrid) are two-component fuels in which the components, being in different aggregate states, can be liquid, solid or gaseous. Due to the complexity of the taxiway layout, hybrid RTs are used to a limited extent.

The Strategic Missile Forces' RD ICBMs use both high-boiling self-igniting liquid fuel fluids (mainly N2O4+H2NN(CH3)2) and mixed fuel rocket engines. LRTs are used in the taxiways of ampulized silo-based missiles, and TRTs are used in the taxiways of both silo-based and mobile-based missiles.

Table 1. Main characteristics of two-component liquid propellants at p k / p a = 7/0.1 MPa

Table 2. Principal composition and main characteristics of ballistic TRT

Solid rocket fuel is a solid substance (a mixture of substances) that can burn without air and at the same time release many gaseous compounds heated to a high temperature. Such compositions are used to create rocket engines.

Rocket fuel is used as an energy source for In addition to solid fuel, there are also gel-like, liquid and hybrid analogues. Each type of fuel has its own advantages and disadvantages. Liquid fuels are single-component and two-component (fuel + oxidizer). Gel fuels are compositions thickened to a gel state with the help of Hybrid fuels are systems that include a solid fuel and a liquid oxidizer.

The first types of rocket fuel were solid. Gunpowder and its analogues were used as a working substance, which were used in warfare and to create fireworks. Now these compounds are used only for the manufacture of small model rockets, as rocket fuel. The composition allows you to launch small (up to 0.5 m) rockets to several hundred meters in height. The engine in them is a small cylinder. It is filled with a solid flammable mixture, which is ignited with a hot wire and burns for only a few seconds.

Solid rocket fuel most often consists of an oxidizer, a fuel and a catalyst that allows it to maintain stable combustion after the composition is ignited. In the initial state, these materials are powdery. To make rocket fuel out of them, it is necessary to create a dense one that will burn for a long time, evenly and continuously. Solid rocket engines use: as an oxidizer, (carbon) as fuel, and sulfur as a catalyst. This is the composition of black powder. The second combination of materials that are used as rocket fuel are: Berthollet salt, aluminum or magnesium powder and sodium chlorate. This composition is also called white powder. Solid combustible fillers for military missiles are divided into ballistic (nitroglycerin compressed gunpowder) and mixed ones, which are used in the form of channel bombs.

A solid propellant rocket engine works as follows. After ignition, the fuel begins to burn at a given speed, ejecting a hot gaseous substance through the nozzle, which provides thrust. The fuel in the engine burns until it runs out. Therefore, it is impossible to stop the process and turn off the engine until the filler burns out completely. This is one of the serious disadvantages of solid fuel engines compared to other analogues. However, in real space ballistic carriers, solid propellant materials are used only at the initial stage of flight. At the next stages, other types of rocket fuel are used, so the disadvantages of solid propellant compositions do not pose a significant problem.