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Eaton Char-Lynn Motor - Solid Rocket Motor : Principle Structure


The Eaton Char-lynn Motor solid rocket motor is a chemical rocket engine that uses solid propellant. Solid propellants include polyurethane, polybutadiene, hydroxyl terminated polybutadiene, nitrate plasticized polyether, and the like.

  The solid rocket motor consists of a fuel column, a combustion chamber, a nozzle assembly, and an ignition device. The drug column is a hollow cylinder made of a propellant and a small amount of additives (the hollow
portion is a combustion surface, and its cross-sectional shape is circular, star-shaped, etc.). The column is placed in a combustion chamber (generally the engine housing). When the propellant is burned, the combustion chamber must withstand a high temperature of 2,500 to 3,500 degrees and a high pressure of 102 to 2 x 107 Pa, so it must be made of high-strength alloy steel, titanium alloy or composite material, and between the grain and the inner wall of the
combustion. Equipped with thermal insulation.

  Ignition devices are used to ignite the charge, usually consisting of an electric fire tube and a gunpowder box (black powder or pyrotechnic charge). After the power is turned on, the black powder is ignited by the electric heating wire, and then the black powder is used to ignite the medicine.

  In addition to accelerating the gas to accelerate the thrust, the nozzle is often combined with the thrust vector control system to control the thrust direction. The system can change the gas injection angle to achieve a change in thrust direction.

  When the column is burned, the engine stops working.

  Compared with liquid rocket engines, solid rocket motors have the advantages of simple structure, high propellant density, and propellant can be stored in the combustion to be used and easy to operate. The disadvantage is that the "specific impulse" is small (also called the specific thrust, which is the ratio of the engine thrust to the weight of the propellant consumed per second, in seconds). The solid rocket motor has a specific stroke of 250 to 300
seconds, and the working time is short. The acceleration is too large, which makes the thrust difficult to control, and the repeated starting is difficult, which is not conducive to manned flight.

  Solid rocket motors are mainly used as engines for rockets, missiles and sounding rockets, as well as booster engines for spacecraft launches and aircraft takeoffs.

  The solid rocket motor is mainly composed of four parts: shell, solid propellant, nozzle assembly and ignition device. The solid propellant formula and molding process, nozzle design and materials and manufacturing process, shell material and manufacturing process are the most The key link directly affects the performance of the solid engine. The performance of a solid engine mainly depends on both thrust and specific impulse. For engines with special requirements such as ballistic missiles or anti-missile interceptor, it also pursues fast-burning performance.

  The materials used in solid engine housings have evolved from high-strength metals (ultra-high-strength steels, titanium alloys, etc.) to advanced composites that are always high-performance carbon fibers. However, for
space launches, solid rocket engines do not pursue the weight reduction of the casing too much, so many solid rockets still use high-strength steel as the casing, such as the S-125 booster used by the Indian GSLV rocket, using the
M250. High strength steel. Lightweight high-strength carbon composites are mainly used on ballistic missiles, especially third-class engines.

  The propellant of a solid engine can be divided into low-energy, medium-energy, high-energy propellants according to energy. The specific impulse is greater than 2,450 N/s/kg (250 seconds) for high energy,
2255 N/s/kg (or 230 seconds) to 2,450. / sec / kg for medium energy, less than 2255 N / s / kg for low energy; according to the characteristic signal is divided into smoke, micro smoke, smokeless propellant, in general, smokeless
propellant relative to smoke propellant, will There is no small loss compared to the rush; according to the material formula combination can be divided into single base, double base, composite propellant, single base propellant has a
single compound composition, such as fire cotton, the ratio is too low is not applicable. The double-base propellant consists of fire cotton or nitroglycerin and some additives. The specific pressure is still insufficient and the
application is not much. The composite propellant is a combination of a separate combustion agent and an oxidant material. The liquid polymer binder is used as a fuel, a crystalline oxidant solid filler and other additives are added, and the mixture is solidified into a multi-phase object. In order to increase energy and density, some powdery light metal materials may be added as a combustible agent, such as aluminum powder. The composite propellant is usually named after the chemical name of the binder fuel, such as HTPB (hydroxyl polybutadiene), and the oxidant is mainly a perchlorate such as ammonium perchlorate. Composite propellants are generally cast and are the absolute mainstream of solid propellants. In addition, modified double-base propellants include composite modified double-base propellant (CMDB) and cross-linked modified double-base propellant (XLDB). On the basis of the double-base propellant, the proportion of the basic component fire cotton and nitroglycerin is greatly reduced, and the
high-energy solid components such as the oxidant perchlorate and the fuel aluminum powder are added, and the composite modified double-base propellant is further The addition of a polymer compound as a crosslinking agent becomes a crosslinked modified double-base propellant. NEPE (Nitrate Plasticized Polyether) in cross-linked modified double-base propellant is the most practical solid propellant. The third-stage engine of China's DF-31A missile is NEPE
China No. N) -15) Propellant.

  The rocket engine nozzle is a convergent-diffusion type nozzle (ie, Laval-DeLaval nozzle), which is composed of an inlet section (convergence section), a throat (throat liner), an outlet cone (diffusion section or an expansion section), and its function It is the conversion of the thermal energy of the combustion products into the kinetic energy of the high-speed jet to generate thrust. The expansion ratio, that is, the area ratio of the throat and the spout, directly affects the performance of the engine, and the well-designed nozzle has a great influence on the performance of the engine. In addition, unlike the liquid engine, which uses a cooling nozzle, the solid engine uses an ablation nozzle. The inner wall of the nozzle is coated with ablation material, which absorbs heat through ablation evaporation of the material to prevent the nozzle from overheating and burning. In general, bell nozzles are used in the expansion section of the engine nozzle.

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