مهندسی مکانیک - Jet Engines
مطالب خواندنی پیرامون مکانیک و تکواندو

Jet Engines

That which separates an airplane from a glider is the presence of some sort of engine or motor. Before the invention of powered flight by the Wright brothers, gliders and balloons were the only way to fly. The Wright brothers took the idea of a glider and added an engine to it. They riggd the engine up to turn a propeller and the prop. pulled the airplane into the air. From that time on, until the advent of W.W.II, the propeller was the only way known of providing thrust for an airplane. When W.W.II broke out, both sides rushed to design the best aircraft possible. During the developement process of designing faster fighter aircraft, German engineers developed a new type of engine capable of propelling an airplane at immense speeds and has since become the only known for getting an airplane up to, and beyond, the speed of sound. There are a number of different types of jet engine, these are:

A diagram explaining how a Ramjet works
  • Ramjet: Ramjets work by having air pushed in to a chamber where it is compressed. In this chamber the air, which was heated by compression, is mixed with fuel. The fuel is ignited by the heated air and creates hot expanded gas is forced out of the exhaust. The ramjet cannot start by itself its needs to gain speed to compress the air, so it must be started out. The ramjet is generally not used in planes because it runs at a high steady speed. Although the it is used in such things as cruise missiles.

  • Turbojet: In a turbojet the air is sucked into the intake and pushed into the compression chamber by a series of compression fans. It is then mixed with fuel that is added through fuel injectors. Then the high temperature of the hot air ignites the fuel which creates hot gas which rapidly expands and pushes towards the exhaust. This gas is pushed past a turbine, the turbine is what turns the compression fans. After that the remaining gas is forced out of the exhaust and creates the thrust of the jet. A jet can create anywhere from 2,500 to 30,000 pounds of force.

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  • Pulse Jet:The pules jet was one of the earliest forms of jet propulsion. It was used by the Germans during W.W.II in their V-1 rockets. The theory it works on is very simple. It has inlet valves that let in air. These valves are spring loaded in the open position. The valves let in air that is heated by burning fuel. These burning gases expand and force the inlet valve closed and the gases are then pushed out the outlet duct to produce thrust. In the absence of burning gas the inlet valves open and let in more air and the cycle repeats. This charge then fire procedure give it a pulse of thrust and then a short stop thus its name the pulse jet.

  • Turbofan:Another commonly used kind of jet propulsion is the turbofan. This kind of jet is used on most large jet liners such as the 747, 727, 767, and 737. This engine is basically the same as the turbo jet except the central fan axle is also connected to a large fan in front of the engine. This fan pushes air into the jet but it also pushes air around the jet creating more thrust.
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