A complex air system is built into most turbine based jet engines, primarily to cool the turbine blades, vanes and discs.
Air, bled from the compressor exit, passes around combustor and is injected into the rim of the rotating turbine disc. The cooling air then passes through complex passages within the turbine blades. After removing heat from the blade material, the air (now fairly hot) is vented, via cooling holes, into the main gas stream. Cooling air for the turbine vanes undergoes a similar process.
Cooling the leading edge of the blade can be difficult, because the pressure of the cooling air just inside the cooling hole may not be much different from that of the oncoming gas stream. One solution is to incorporate a cover plate on the disc. This acts as a centrifugal compressor to pressurize the cooling air before it enters the blade. Another solution is to use an ultra-efficient turbine rim seal to pressurize the area where the cooling air passes across to the rotating disc.
A series of (e.g. labyrinth) seals allow a small flow of bleed air to wash the turbine disc to extract heat and, at the same time, pressurize the turbine rim seal, to prevent hot gases entering the inner part of the engine.Small quantities of compressor bleed air are also used to cool the shaft, turbine shrouds, etc.
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JET ENGINE
How does a jet engine work?
A jet engine uses a gas turbine to drive a fan that sucks in air, mixes it with burning fuel, and then blasts the expanded air-gas mixture out the back.
Because every action has an equal and opposite reaction, as the air streams backward the engine is forced forward.
turbine
Safety and reliability
Jet engines are usually very reliable and have a very good safety record. However failures do sometimes occur.The most likely failure is compressor blade failure, and modern jet engines are designed with structures that can catch these blades and keep them contained them within the engine casing. Verification of a jet engine design involves testing that this system works correctly.
model jet engine
combustion chamber
diagrams
In order to understand how an engine works..
we first need to understand the process of combustion. Combustion is defined as the burning, or oxidation, of matter to produce energy. Two substances are necessary for combustion to occur--a fuel and an oxidizer. A fuel can be anything from the wood, coal, or natural gas used to produce heat in a furnace to gasoline or hydrogen used in an internal combustion engine. An oxidizer, as its name implies, is a substance that contains oxygen.
The purpose of both the jet engine and the rocket engine is to combust a mixture of fuel and oxidizer. This combustion process generates a high-pressure exhaust that creates thrust to push a vehicle forward. The fundamental difference between the two types of engines, however, is where the oxidizer comes from.
A jet engine obtains its oxidizer from the external atmosphere, as illustrated in the diagram below. Air enters the engine through an inlet and is then slowed down and compressed by a series of compressor blades. The compressed air is then mixed with fuel, typically a petroleum-based liquid similar to kerosene, and burned. The high-pressure gas is exhausted through a nozzle to generate thrust.
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