26-03-2012, 03:33 PM
ROCKET ANATOMY
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. INTRODUCTION:
A liquid rocket engine employs liquid propellants which are fed under pressure from tanks in to a combustion chamber. The propellants usually consist of a liquid oxidizer and a liquid fuel. In the combustion chamber the propellants chemically react (burn) to form hot gases which are then accelerated and ejected at high velocity through a nozzle, thereby imparting momentum to the engine. Momentum is the product of mass and velocity. The thrust force of a rocket motor is the reaction experienced by the motor structure due to the ejection of the high velocity matter. This is the same phenomenon which pushes a garden hose backward as water squirts from the nozzle or makes a gun recoil when fired.
PROPELLANT CHOICE:
Liquid rocket engines can burn a variety of oxidizer - fuel combinations, some of which are tabulated in Table I. Most of the propellant combinations listed is dangerous, toxic, and expensive. The amateur builder of rocket engines on the other hand, requires propellants that are readily available, reasonably safe and easy to handle, and inexpensive. Based on experience, ROCKETLAB recommends the use of gaseous oxygen as the oxidizer and a hydrocarbon liquid as the fuel. They give good performance, the combustion flame is readily visible, and their high combustion temperature presents an adequate design challenge to the amateur builder. The propellants are used in the Atlas missile and the Saturn space booster. In these systems, however, liquid rather than gaseous oxygen is used as the oxidizer.
3.3 Chamber Wall Thickness:
The combustion chamber must be able to withstand the internal pressure of the hot combustion gases. The combustion chamber must also be physically attached to the cooling jacket and, therefore, the chamber wall thickness must be sufficient for welding or brazing purposes.
Heat Transfer:
The largest part of the heat transferred from the hot chamber gases to the chamber walls is by convection. The amount of heat transferred by conduction is small and the amount transferred by radiation is usually less than 25%, of the total. The chamber walls have to be kept at a temperature such that the wall material strength is adequate to prevent failure. Material failure is usually caused by either raising the wall temperature on the gas side so as to weaken, melt, or damage the wall material or by raising the wall temperature on the liquid coolant side so was to vaporize the liquid next to the wall.
Materials:
The combustion chamber and nozzle walls have to withstand relatively high temperature, high gas velocity, chemical erosion, and high stress. The wall material must be capable of high heat transfer rates (which mean good thermal conductivity) yet, at the same time, have adequate strength to withstand the chamber combustion pressure. Material requirements are critical only in those parts which come into direct contact with propellant gases. Other motor components can be made of conventional material. Once the wall material of an operating rocket engine begins to fail, final burn-through and engine destruction are extremely rapid. Even a small pinhole in the chamber wall will almost immediately (within one second) open into a large hole because the hot chamber gases (4000-6000 F) will oxidize or melt the adjacent metal, which is then blown away exposing new metal to the hot gases.
CONCLUSION
In above report we are concluded that rockets are using nozzle to generate high
To generate high velocity gases. The rocket engine is basically employees basically operate on the principle of nozzle. By using different propellants in the combustion chamber resulting high pressure gases are expanded through specially shaped nozzles produce thrust failure of rockets is generally occurs due to some of the mentioned mechanical factors such as high pressurized gases low thermal energy levels inherent material properties etc.