Do-it-yourself caramel rocket. How do I make rocket engines. Three manufacturing methods
A few decades ago, when humanity was raving about space exploration, rocket science was rampant. Both schoolchildren and adult men enthusiastically designed in garages and kitchens from improvised materials. Now the hype has subsided a bit, but what could be more exciting than launching your own made aircraft into the air? How to make a rocket take off? The most accessible and practical is to use caramel fuel, a mixture of saltpeter and carbohydrate.
What will be required
The set of components is not so great.
1. Sugar or sorbitol - raw material for caramelization.
2. Saltpeter (you can use different ones, more on that below).
3. Metal container - most often they take ordinary cans, although it is preferable to take dishes with thick walls - for more uniform heating. Even better - enameled or stainless steel, so that there is no reaction of the solution with the material of the dishes.
4. Electric stove - you can't cook fuel on a gas stove!
5. Newspaper or other paper with good absorbent properties (if your goal is to make not just caramel fuel, but caramel paper). It is also used in rocket engines, impregnated with ready-made "caramel" and dried (without heating).
6. Protective equipment: goggles and gloves.
7. Ventilation.
Three manufacturing methods
You can make caramel fuel in different ways. The easiest thing is to just mix the ingredients. Another "caramel" is boiled - simply or with evaporation. With normal mixing, the fuel is poured into a glass jar and shaken several times, then tightly closed to prevent water absorption. When used directly in rocket engines, this type of fuel must be well compacted, otherwise an explosion is possible.
Boil, or rather, melt caramel fuel at a temperature of 120-145 degrees until the sugar is completely converted and a mass is formed that is similar in consistency to liquid semolina. It is not necessary to pre-grind the components. It is very important to constantly stir it so that air bubbles do not form. Evaporation cooking involves adding water and then evaporating it. The disadvantages of this method: moisture remains in the fuel, and this reduces the rate of its combustion.
Recipe #1
Caramel fuel from is the best option. The ingredients are taken in the following proportions: sugar or sorbitol - 35%; saltpeter - 65%. Saltpeter is dried in a flat wide frying pan about 100-150 degrees for about two hours. Then grind for about 20 seconds - you can use a mortar or coffee grinder.
Lay in equal portions, 50 grams each. In order not to bother with grinding sugar, it is better to buy ready-made powdered sugar. For "boiled" caramel fuel, nothing needs to be ground or dried. To increase efficiency, 1% iron oxide (Fe 2 O 3) can be added to the mixture.
Recipe number 2
Caramel fuel from sodium nitrate. Features of this mixture - it is more hygroscopic. It will take 70% saltpeter, 30% sugar and two volumes of water (200%).
Recipe number 3
It is not recommended to use it. fuel for (ammonium nitrate). Why is it better to pay attention to other recipes? Because this is an unstable connection, and when heated, anything can go wrong. As a result, the idea is likely to end in a fire!
In addition, in the manufacture of "caramel" from ammonium nitrate, extremely toxic fumes are released. Therefore, all recipes using ammonium nitrate contain additional components to convert it to sodium or potassium. The easiest option is with sodium. We take 40% saltpeter, 45% baking soda and 200% water. We note the liquid level and evaporate until the smell of ammonia disappears. Then we add water to the original level (it has also partially evaporated), add 15% sugar and wait for it to dissolve.
Catalysts
To increase the effectiveness of "caramel", various catalysts are added to it. The most popular is iron oxide. Less known caramel fuel with aluminum. Attention! A mixture of aluminum and nitrates may ignite in the presence of water. Especially dangerous is the presence of any alkaline impurities that may be present in saltpeter that is not pure enough or made by yourself. Therefore, in a fuel based on nitrates with aluminum as a catalyst, it is necessary to add 0.5-1% of some weak acid, and it is not a fact that this amount is enough - it all depends on the quality of the saltpeter. Boric is the best option. Oxalic and acetic are not suitable - aluminum reacts with them. If during the cooking process the mixture becomes very hot, foams and emits a strong smell of ammonia, you must immediately remove it from the stove and immerse it in water.
In general, it is better for experienced rocket scientists who have mastered the simplest types of fuel to experiment with catalysts. Yes, and it doesn’t hurt to learn chemistry: it’s easy to use ready-made tips, but knowledge and understanding of what you are doing and what reactions occur in the mixture is much more valuable.
Aluminum is added to the potassium caramel. Permissible variations are from 2.5 to 20%. A different amount gives a different change in the burning rate of the fuel. It is recommended to use spherical aluminum ASD-4.
How to stay whole and healthy
The most dangerous way to prepare caramel fuel is by melting sugar and saltpeter, but this option is also the most effective. The container in which the "caramel" is boiled must be perfectly clean - foreign substances can cause a fire.
There should not be sources of open flame nearby - we don't need explosions in the kitchen. It is very important to monitor the temperature of the mixture - it should not rise above 180 degrees under any circumstances!
When stirring, it is better to use a wooden stick to avoid adverse reactions. It should be mixed very carefully, but evenly: air bubbles in the finished fuel, when used, lead to an explosion of the rocket. When pouring this fuel into molds, you also need to make sure that there are no bubbles. It is necessary to work with a hood or in the fresh air, especially for the recipe with ammonium nitrate.
Do not grind sugar and saltpeter together in a coffee grinder! You need to grind separately, mix, shaking, in a glass bowl.
Beginners should not mess with ammonium nitrate: first try the simplest and safest (based on potassium nitrate) caramel fuel. The manufacture of any homemade fuel must take place under the most careful control of the quality of ingredients, temperature, moisture content and in compliance with all safety measures!
Where to get the ingredients
Saltpeter is sold in agricultural supply stores and departments for summer residents as a fertilizer. Sorbitol is a sugar substitute for diabetics. Sold, respectively, in a pharmacy. Fe 2 O 3 - iron oxide - used to be sold under the name You can try to make it yourself by studying the relevant literature. Mineral hematite - this is also aluminum sold by chemical reagent manufacturers.
Standard blended solid propellants are out of reach for most rocket enthusiasts. We have to look for something simpler ... First you need to decide where space begins - where, in fact, you need to get. In recent years, it has been more or less agreed to consider that space begins at a height of 100 km. Although this is not entirely true - such an altitude is not enough for an orbital flight - but round numbers are psychologically attractive, so the 100-kilometer boundary suits most arguing.
Edition PM
First amateur space launch
Steve Bennet and his brainchild - the Starchaser Nova rocket
To space on the cheap
Nevertheless, the founders of the Cheap Access To Space Prize, or CATS Prize for short, were more decisive - in order to receive the prize, you need to deliver a payload of 2 kg to an altitude of 200 km. The competition started in November 1997, and in order to receive a prize of $ 250,000, it was necessary to have time to reach this height before November 8, 2000. More than 30 attempts were made, but no one managed to climb above 25 km, and the prize was never awarded. No one could claim the "consolation" prize of $25,000 for reaching a height of 125 km. Some of the teams continued to work even after the deadline - the impetus that the CATS Prize gave to amateur rocket science cannot be overestimated. Some teams have become real commercial firms, but they don’t make rockets anymore ...
space stuntman
Only one team - CSXT, led by former Hollywood stuntman and special effects artist Kai Michelson - continued to work, trying to achieve the original goal. Michelson, known in narrow circles under the name The Rocketman for his commitment to jet propulsion, even after going on vacation, continued his favorite pyrotechnics. After analyzing the failures of its predecessors, CSXT abandoned the exotic launch schemes from a stratostat or aircraft.
Balloon launches date back to the 1950s. Attempts to save on atmospheric losses were made even before the flight of the first satellite, but, both in the 1950s and in the 1990s, the result was unsatisfactory - a seemingly simple scheme was fraught with a lot of "rakes" that unsuccessful rocket scientists and through 40 years came with the same enthusiasm.
Kai Michelson also had to abandon the two-stage design - its reliability in amateur performance left much to be desired, as he was convinced during an unsuccessful attempt to reach the edge of space in 1997. The second stage simply did not start. In addition, after the unsuccessful starts of the CATS Prize contestants, obtaining permits to launch two-stage high-altitude rockets was surrounded by almost irresistible slingshots for amateurs.
Space pass
In fact, American laws governing amateur rocket science are the most liberal in the world. In addition to the usual rocket models launched around the world, the High Power Rockets classes are defined in the USA and, for those who lack this, Experimental Rockets. The classification is based on both the total impulse of the engine (the product of thrust and the time of operation) and the launch mass and allows - with certain reservations - amateur rockets up to 16,000 N s in the High Power Rocketry class and up to 128,000 N s in the Experimental Rocketry class. Compare this to the maximum 80 Ns in rocket modeling competitions! In Europe, there is nothing like it for lovers of large rockets, so the European flight altitude record is still less than 10 km. Not only that, European amateurs are forced to take their rockets to the USA, equip and launch them in Nevada!
But even in the desert, laws monitor safety very carefully. Fans are forbidden to transport large charges from state to state - you need to equip the rocket right at the launch site. There are a lot of other restrictions that seem far-fetched at first glance, but most of them were created during the analysis of some kind of accident and are designed to eliminate such accidents in the future.
flying nail
All that Michelson could improve was rocket aerodynamics and fuel characteristics. CSXT has done a lot of research and development to achieve maximum performance. The scope of tests of engines of various calibers was unimaginable for most amateurs - more than a dozen home-made 6 and 8 caliber solid propellant rocket motors (15-20 cm) burned out during tests while trying to achieve reliable operation at the peak of their capabilities. They say the team's expenses exceeded $130,000! But finally, in January 2002, a rocket capable of reaching space was ready. She received the name Primera, in honor of the sponsoring company, the manufacturer of CDs. Only on June 1, it was possible to obtain permission to launch - however, it did not take place due to weather conditions. A new attempt at the end of September needed a new permit, which was received on 27 August. But on September 21, 2002, this rocket, having managed to rise to 720 m and gain speed of 1700 km / h in just three seconds, collapsed in the air due to burnout of the engine housing near the nozzle and the rocket turning across the flow.
Improvements and production of a new rocket, called GoFast, took a year and a half. The rocket became one and a half times heavier and weighed 328 kg at the start (of which 197.5 kg weighed fuel). The length of the rocket was 6.4 m, and the diameter of the body was only 25.4 cm, that is, the rocket looked as thin as a nail! In professional rocketry, such proportions are almost never found, but it was necessary at all costs to reduce aerodynamic drag, which at hypersonic speed is achievable only by reducing the diameter. Yes, yes, the rocket had to gain hypersonic speed even in a dense atmosphere - at an altitude of about 8-10 km, where conventional subsonic airliners fly. Therefore, her nose was a solid steel cone with a very small opening angle and thin at the top - the turner managed to carve this detail only on the third attempt.
First record
This time, fate was more favorable to the team. On May 15, 2004, with a monstrous acceleration of 21.5 g (more than that of a fighter pilot rescue catapult), a thin rocket rushed to the edge of space. Attracted observers by radar tracked the speed and height of the rocket. After 13 seconds, the fuel in the engine completely burned out and the rocket flew by inertia at a speed 5.2 times the speed of sound. It became clear that the record would take place. After 2.5 minutes, the rocket reached space. Five minutes after the launch, radio beacon signals were received - the payload module descended by parachute. Unfortunately - far from the estimated landing site. It was possible to find him when the batteries of the lighthouse were already exhausted. And the body of the accelerator had to be searched for more than two weeks - it fell 40 km from the launch site. These difficulties somewhat overshadowed the success, but the height of 115 km was taken, which, in addition to the radar, was now evidenced by the records of the onboard "black box"!
Almost a shuttle
But back to sugar. The fuel used in the GoFast rocket was the closest amateur approximation to the Shuttle Launch Booster (SRB) fuel. A typical mixed solid fuel consists of ammonium perchlorate, aluminum and synthetic rubber, initially liquid, solidifying directly in the engine. But ammonium perchlorate and rubber are substances that are practically inaccessible to most "rocket lovers". Their sale is under very serious control. Yes, and aluminum powder is not needed anyhow - "silver", for example, is not good, metal particles must have a spherical shape and a certain size.
Caramel
As a result, engines on such fuel, even in the United States, are available only to a few. The rest have to use something simpler. For example, the notorious sugar. "Caramel" rocket fuel is indeed an alloy of sugar and potassium nitrate. Its characteristics are modest, but still it is one and a half times better than the black powder known to everyone, on which rockets flew for almost a thousand years before pyroxylin was invented. In addition, "caramel" is at least 10-20 times cheaper than fuel based on ammonium perchlorate. Who came up with the "caramel" fuel is now difficult to establish, it appeared in the middle of the 20th century. American sources claim that it was first used by Bill Colburn in 1943 in California. Rare books about amateur rocket science did not reproduce its recipe, but its use was put on a scientific basis only in the mid-1990s - amateurs began to study the properties of the fuel, the dependence of its characteristics on the composition variation, on the initial temperature, pressure in the chamber, etc. Of course, professionals have energetically more favorable substances at their disposal, but amateurs needed all this information for serious and safe use, and they could only be obtained experimentally.
Not sugar
It turned out that this fuel stably burns in a wide range of pressures in the chamber, which made it possible to make on it both the simplest paper engines and rechargeable metal ones. Small deviations in the composition also do not interfere with its good work, so it is safer. However, this fuel also has disadvantages, first of all, it is fragility. For example, rubber-based fuels are very soft, professional rocket scientists
they say that you can pinch off a crumb from a piece of such fuel with your hands, this allows you to tightly fasten the charge to the body. The charge also serves as thermal protection - until it burns out completely, the engine case does not heat up. You can’t do this with caramel - it can crack under working pressure reaching up to fifty atmospheres! Therefore, the caramel charge is a supplementary charge; there should be a narrow gap between it and the body to equalize the pressure. But at the same time, the metal case must be protected from hot gases, because their temperature reaches almost 1400˚C, so the metal will inevitably lose strength.
Another disadvantage of "caramel" is a large amount of "condensed phase". This is how rocket scientists call combustion products that are not gases. Burning caramel produces potash, or potassium carbonate. In the chamber, it is liquid, and in the nozzle it becomes solid. The smallest particles of potassium carbonate create dense white smoke. This smoke is quite caustic, as potash is alkaline. Therefore, in no case should you burn "caramel fuel" indoors. But for a rocket engine, the condensed phase is harmful for another reason: solid or liquid particles cannot expand in the nozzle, like gases, and therefore do not create work; heat from them to the gas is transferred only by radiation, so the efficiency of the rocket engine decreases. This means that the actual specific impulse of "caramel" is noticeably lower than the theoretical one, calculated from the heat of chemical reactions.
And one more serious drawback - for classic sugar caramel, the temperature difference between the melting of sugar and the ignition of the finished mixture is too small. But this problem was successfully solved by replacing sugar with sorbitol. Sorbitol fuel burns more slowly than sugar, but it is much safer to work with, because sorbitol melts already at 125˚C, and sucrose only at 185˚. All other useful properties of sugar fuel have been preserved in sorbitol.
On parole
After the triumph of GoFast, many rocket scientists made claims to the CSXT team. They say that their rocket is “dishonest” because it cannot be reproduced by almost any amateur, and besides, due to the large deflection of their rocket, high-altitude launches are now under much tighter control: US officials have decided that their legislation is too liberal. But on the other hand, it is much easier to solve a problem once solved a second time. And Canadian Richard Nakka, one of the main enthusiasts of "caramel", decided to achieve an "honest" result from the point of view of amateur rocket science, to reach the edge of space on sugar - or sorbitol - fuel. The project was called Sugar Shot to Space, loosely translated "On sugar into space."
But first it was necessary to find out whether this problem can be solved in principle. If the atmosphere did not interfere, a speed of 1400 m / s would be enough to “jump” from the surface of the Earth to a height of 100 km. But at GoFast, the atmosphere “ate” about 300 m/s (more than 1000 km/h!). To reduce the amount of losses, it is necessary to accelerate in more rarefied air, at a higher altitude, and for this it is necessary to reduce the starting overload and increase the engine operating time. But for an unguided rocket, this is undesirable, since the area on which the stabilizers do not work well increases. It is necessary to increase either the height of the guide or the size of the stabilizers, which increases the aerodynamic losses.
Your profile
The analysis of aerodynamics was carried out very carefully, as a result, the proportions of the rocket turned out even more strange than those of GoFast - the length is 30 times the diameter, three stabilizers instead of four, and they tried to optimize the shape of the nose. But all this did not bring closer to the desired result. I did not want to make a two-stage rocket, as this reduced reliability and increased the difficulty in obtaining permission to launch. Richard Nakka was familiar with these problems firsthand.
It was necessary to come up with such a thrust profile (dependence of thrust on time), which could be implemented in a caramel engine and which would reduce aerodynamic losses and not increase gravity losses too much. Anti-aircraft missiles use a fast launch stage with a thrust of a hundred tons and an acceleration of up to 50 g (in anti-missile systems) and a relatively "long-playing" march stage - with much less thrust. But the sustainer stage used to be made on a liquid-propellant rocket engine, and now it is on special solid fuels that provide a long time of operation. This is not suitable for amateurs - the volume of developmental tests is too large. For simple caramel engines, the operating time is closely related to the diameter.
ballistic pause
But the solution was found - it became a two-stage engine. Such an engine consists of two chambers with two charges of fuel, working in turn on a common nozzle. Between the chambers there is a plug made of combustible material, which should not allow hot gases to reach the second charge during the operation of the first. After the first stage burns out, the rocket will fly upward by inertia for some time, gradually losing speed, but also getting out of the dense layers of the atmosphere, and only after the end of the ballistic pause will the second half of the fuel supply ignite. In this case, the maximum speed will be noticeably lower than that of GoFast, and it will be possible to achieve it at a higher altitude - while aerodynamic losses will decrease.
However, with all the tricks, the launch mass and dimensions of a sugar-fueled rocket must be greater than that of a perchlorate-rubber rocket. Therefore, members of the SS2S group first built a model of a two-stage engine on a scale of 1:4 (in linear dimensions; in terms of fuel mass, this is 1/64). Only on the fourth attempt did they succeed - the most difficult thing was to ensure that the chamber of the first stage did not burn out during the operation of the second, because it received a double dose of heat load.
However, having overcome all the difficulties, rocket scientists realized that before building a full-sized rocket for storming space, they would first have to work out technical solutions on something cheaper, and now they are building a rocket on a 1:3 scale. The path of lovers into space is long! But we hope that over time they will succeed, and we wish them perseverance and success.
Racket fuel is made from saltpeter and newspapers.
You can use any saltpeter:
- POTASSIUM nitrate: KNO3 - also known as potassium nitrate, potassium nitrate, potassium nitrate, Indian nitrate (suitable in all respects).
- SODIUM nitrate: NaNO3 - it is also sodium nitrate, sodium nitrate, Chilean nitrate (it can become damp at high humidity)
- AMMONIUM NITER: NH4NO3 - aka ammonium nitrate, ammonium nitrate, ammonium nitrate, nitrogen fertilizer (recipe with conversion)
- CALCIUM nitrate: Ca (NO3) 2 - aka calcium nitrate, calcium nitrate, lime nitrate, Norwegian nitrate (recipe with conversion)
Making a saltpeter solution for impregnating newspapers
- Take any container of suitable size for measuring (cap, vial, glass, jar or bucket ;-) Don't do too much the first time! If saltpeter in granules is larger than buckwheat, grind it to the size of table salt before measuring. Sugar is measured in the form of sand. You need to measure as follows: Dial a full measure with a slide and press it to compact (by hand), fill it up and press it again. When the contents stop compacting, fold the excess evenly along the edge of the measure with a ruler or pencil body. This will be one measurement (percentages by weight are indicated in brackets).
Saltpeter Recipes
For potassium nitrate:
3 volumes of saltpeter + 1 volume of sugar
Sequencing:
- Measure: 3 saltpeters (80%), 1 sugar (20%) and 3 times more water (12 measures, 300%).
The solution is ready.
For sodium nitrate:
2 saltpeter + 1 sugar
Sequencing:
- Measure: 2 saltpeter (70%), 1 sugar (30%) and 2 times more water (6 measures, 200%).
- Heat with stirring until completely dissolved.
The solution is ready.
For ammonium nitrate with conversion to sodium:
2 saltpeter + 2 baking soda (NaHCO3) or 1 washing soda (Na2CO3) + 1 sugar
Sequencing:
- Ensure good ventilation!
- Measure: 2 saltpeter (40%), 2 baking soda (45%) or 1 washing and twice as much water (8 or 6 measurements, 200%).
- Boil for about an hour until the smell of ammonia almost disappears.
- Add 1 part sugar (15%).
The solution is ready.
In order not to spoil the air in the room with ammonia released as a result of the reaction with soda, cook under a hood or outdoors! If this is not possible, a jar of solution can be placed outside the window on the windowsill. For heating, you can use a small boiler.
For ammonium nitrate with conversion to potassium:
3 saltpeter + 3 potassium chloride (KCl) or 1 potassium carbonate (potash) (K2CO3) or 1 potassium sulfate (K2SO4) + 1 sugar
Sequencing:
- Measure out: saltpeter, potassium and twice as much water.
- Pour into any suitable container and mark the level.
- Boil for about an hour.
- Pour again into the container with the marked level and add water to the mark.
- Add 1 part sugar.
The solution is ready.
For calcium nitrate with conversion to sodium or potassium:
3 saltpeter + 3 baking soda or potassium sulfate or potassium sulfate + 1 sugar
Sequencing:
- Measure out: 3 saltpeter, 3 soda or potassium and twice as much water (12 measures).
- Heat up while stirring. The solution will become cloudy white.
- Let stand. The resulting chalk will precipitate.
- Carefully drain the saltpeter solution from the sediment.
- Discard the sediment.
- Add 1 part sugar to the solution.
The solution is ready.
Newspaper impregnation
If you burn a piece of caramel paper folded several times or rolled into a roll for testing, it should burn actively in about 3 to 5 seconds. with neon flame. In one layer, it can burn unstable and even go out.
Potassium nitrate can be used as rocket fuel for homemade rockets. We are talking about simple rackets that are assembled in a couple of minutes, on the knee.
First, about rockets.
The amount of gases released during the combustion of saltpeter with sugar is enough to lift a homemade rocket or pyrotechnic projectile into the air. But if the body of the rocket is too heavy, then it may not take off. Pressed cardboard tubes can be used to make the case. They can be taken from used pyrotechnic products, from the film in which the sausage is wrapped in stores, you can glue a couple of layers of cardboard yourself, just use silicate (stationery) - it is not combustible and heat-resistant. Good as a material in pyrotechnics aluminum foil for baking. You can completely make a rocket out of foil, but it is soft and so that it does not unfold with great pressure, it is pulled with a soft wire. The wire is also used to form a nozzle, from where a jet of flame will come from. In order for the rocket to fly smoothly, it needs a stabilizer (tail) in the form of a long stick. It is easiest to tear it off from a used Chinese rocket, or cut off and dry an even twig in the forest. As a fuse, I use a newspaper soaked in a solution of potassium nitrate. I prepare it in advance, roll it into a tube, bend it and plug the nozzle with it so that the fuel does not spill out.
Now about fuel
Potassium nitrate burns well with sugar. We mix the proportions of 5 parts of saltpeter and four sugars, for every 100 gr. saltpeter can be added 5 gr. soda. All fuel is ready.
If you bother about improving the combustion of the mixture, I advise you to grind all the ingredients in a coffee grinder. You can grind them together, mix even better. This is not dangerous. Having poured the mixture into a cardboard tube, you can tamp it down by tapping it with something flat, with an object close in diameter. I heard that burning will be better if, in a compacted mixture, leave a hole with a diameter of 8-10 mm for the entire length of the mixture. This can be done by inserting a long cylindrical object before tamping. Preferably smooth, so that it is easier to get it later, for example, a felt-tip pen.
You can boil the mixture. Pour water into a small saucepan to just cover the bottom. We turn on a small fire, and begin to pour out in parts, stirring constantly, so that everything has time to melt. The mixture melts, then darkens, resembles caramel - you can remove and pour into molds. Do not overheat the mixture, otherwise it will burn in the pan, so do not leave it unattended on fire. Let the mixture cool, it will harden. You can make long sticks and use them as a wick.
Carry out tests on the street, otherwise the balcony or entrance can be burned down.
By the way, saltpeter burns very well with ground barbecue coal. Maybe even better than sugar. After all, the composition of gunpowder is saltpeter, coal, and a little sulfur. You can also experiment how saltpeter burns with: sorbitol, starch, dry alcohol.
Video demonstrating the burning of saltpeter and sugar
In less than a minute, I concocted a rocket or something, and it crawled along the ground. If the body is lightened, then it is possible to launch it into the sky. It is necessary to try an empty bolonchik with a dezica or a freshener.
Here's a video:
Relating to mixed fuels with an organic binder. The basic, most studied and frequently used composition is 65% KNO 3 and 35% sorbitol (by mass). Such a composition is close to the optimum in terms of the achievable specific impulse at small expansion ratios typical for model solid propellant rocket motors. The moderate exponent in the combustion law makes the fuel suitable for operation in a wide range of pressures, and, as a result, suitable for homemade solid propellant rocket motors with a noticeable spread in geometric characteristics.
The energy characteristics of this composition are very moderate. The theoretical specific impulse of caramel fuel on potassium nitrate is 153 kgf * s / kg, and practically achievable does not exceed 125 units. This is less than that of cheap ballistic fuels based on nitrocellulose, so this composition is not used industrially. However, this is significantly more than that of black powder, in addition, the manufacture of caramel fuel does not require the specific equipment necessary for the production of gunpowder, therefore it is popular with manufacturers of model rocket engines, both artisanal and serial commercial.
The main disadvantages of this fuel are hygroscopicity and a large amount of condensed phase in combustion products. The fragility of this fuel should also be recognized as a disadvantage, which narrows the choice of solid propellant rocket engines with its use. Finally, the disadvantage is significant shrinkage (reduction in volume) during hardening, which can cause distortion of the shape of the checker or peeling of the armor.
When replacing sorbitol in the fuel composition with sucrose, the combustion rate increases quite significantly, by 40% at atmospheric pressure, but other properties of the fuel (density, specific impulse, exponent in the combustion law, etc.) hardly change. The main disadvantage of the sugar composition is the much more dangerous cooking process, as more heat is required.
Caramel fuel is so named because of the use of sugar or sorbitol in its composition, as well as the appearance of the finished fuel. The English term "rocket candy" characterizes the attitude towards it in the same way.
Despite being relatively safe compared to other formulations, caramel fuel requires the same precautions in use as any other rocket fuel, as it is a high-energy formulation.
The original fuel is of low toxicity, but its combustion products can irritate the mucous membranes and respiratory organs, since potassium carbonate, which is released in a highly dispersed form and has an alkaline reaction, can cause a chemical burn even after cooling to room temperature. The combustion temperature of the base composition is approximately 1400 degrees Celsius, which is enough to soften the steel body of the solid propellant rocket engine when exposed to it without thermal protection.
The finished fuel consists of a solid solution of saltpeter in sorbitol and fine particles of undissolved saltpeter suspended in it. The melting point of the finished fuel is much lower than that of the original components. The solubility of saltpeter in sorbite in solid form is much less than in the melt, therefore, when cooling, the fuel gains strength gradually, since the volume of crystals is released from the solid solution, and a certain amount of heat is released. Large checkers remain soft for more than a day.
The pioneer of the use of caramel fuel is considered to be Bill Colburn, who used it for the first time in 1948, and this fuel became widely known in the United States with the release of the book by Bertrand Brinley in 1960. It is widely used in improvised rockets due to the availability of components.
