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RECOMMENDATIONS FOR SELECTING FUEL OIL FOR ENGINES
Sometimes a mixture consisting of 60% potassium nitrate KNОз (saltpeter) is used as well as 40% powdered sugar (by weight), called “caramel fuel”. This is the simplest in the main view, the fuel is able to raise a small rocket (about 300 mm long ) to a height of up to 300 m , but the means of its preparation is very unsafe for hapless pyrotechnics. The difficulty lies in the fact that if both components become entangled at a high temperature, then a slight overheating, as if as well as mixing, is threatened with an explosion.
In addition, poorly crushed and mixed components cracked after drying, resulting in air cracks inside the fuel. After ignition of the fuel prepared in this way, a sudden and uncontrolled increase in pressure in the engine's combustion chamber results, and it also explodes.
The use of the above components in powder form eliminates the risk of an explosion, but requires careful preparation of the engine control as well, as if melted sugar clogs the nozzle also often leads to the formation of cracks in the walls.
Among the many varieties of solid fuels it is difficult to find a completely safe and at the same time high-calorific. Therefore, there is no need to conduct research in this course, and even more so to experiment - this has already been done by experts in return.
For amateur rocket production, only one fuel is recommended, but it is a mixture of zinc and sulfur in the form of finely ground powder. This fuel has already been well studied and tested. Nevertheless, it is intended for relatively large rockets — amateur as well as research ones.
It can also be used in circles working under the guidance of specialist instructors. Powdered zinc mash with sulfur forms a chemical combination - zinc sulfide. The efficiency of this fuel depends on various factors, for example, such as the engine system (especially the nozzle) and even on the humidity and ambient temperature. A mixture of zinc and sulfur ignited by the electrical ignition system is also not sensitive to shock effects.
Dust mixture, rising in the air, acts on the mucous membrane of the nose and the eye. Therefore, when powder is poured, it is necessary to use a dustproof - protecting mask. Attention should be paid to the fact that zinc dust (as well as any metal) in certain thermal conditions can be ignited in contact with the atmosphere.
Therefore, when transferring the powder in large quantities, it is necessary to observe special care. It is necessary to mix components in wooden ware (but in no way in metal), rotating it, as it is the work of workers who mix cement.
The following weight proportion is recommended: 2.04: 1.0 (zinc 2.04; sulfur 1.0) , which follows from the ratio of the atomic weights of both components. The atomic weight of zinc ( Zn ) is 65.38 veins, but sulfur ( S ) is 32.07 . As a result of a chemical reaction occurring in the engine's combustion chamber, zinc sulphide Zn + S = ZnS is formed . Refuel the engine with the fuel you need with a wooden spoon in an open atmosphere or in a well-ventilated place. Due to the danger that lies in the self-made, primitive preparation of rocket fuel, specialists started the development of fuels and engines, as a result of which industrial-model model engines appeared, fueled with precisely calculated energy reserves, also simple in design. However, it is most proud that the engine with industrial fuel alienates the rocket model significantly an impressive guarantee of safety than the best prepared fuel of its own manufacture.