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Gas turbine engines may be classified into the following groups: turbojet engines, turbofan engines, turboprop engines, turboshaft engines.
A turbojet derives its thrust by highly accelerating a small mass of air, which goes through the engine. This engine consists of a diffuser, a mechanical compressor, a combustion chamber, a mechanical turbine and an exhaust nozzle.
The function of a diffuser is to transform the kinetic energy of the entering air into a static pressure rise. The diffuser delivers its air to the mechanical compressor which further compresses the air and delivers it to the combustion chamber. There fuel nozzles feed fuel continuously, and continuous combustion takes place at approximately constant pressure. The high temperature and high pressure gasesthen enter the turbine, where they expand to provide power for the turbine.
The turbine is directly connected to the compressor, and all the power developed by the turbine is absorbed by the compressor and the auxiliary apparatus. The main function of the turbine is to provide power for the mechanical compressor. After the gases leave the turbine, they expand further in the exhaust nozzle and are ejected with a velocity greater than the flight-velocity to produce thrust for propulsion.
Because of turbine material limitations, only a relatively small amount of fuel can be burnt in the combustion chamber. The exhaust products downstream of the turbine still contain a considerable amount of excess oxygen. Additional thrust can therefore be obtained from the turbojet engine by providing an afterburner aft of the turbine. There additional fuel can be burned. Afterburning greatly increases the temperature and hence the velocity of the exhaust gases, providing greater thrust.
According to the type of compressor used turbojets are classified into two general types. These types are the centrifugal-flow compressor and the axial-flow compressor.
According to this principle the turbojets’ names are centrifugal-flow turbojets and axial-flow turbojets, respectively. The operation of both types is basically the same.
Since introduction of turbojets the performance of aircraft engine has been increased phenomenally. They are best for high-speed, high-altitude, long-distance flights. The turbojet engines are now in mass production for various aircraft.
Задание 9. Переведите вопросы на английский язык и ответьте на них.
1. Какие типы газотурбинных двигателей вы знаете?
2. Из каких компонентов состоит турбореактивный двигатель?
3. Какова функция диффузора?
4. Где сжимается воздух?
5. Какая форсунка подает топливо?
6. Какие газы поступают в турбину?
7. Какова функция турбины?
8. Какое количество топлива может быть сожжено в камере сгорания?
9. Как может быть получена дополнительная тяга?
10. Как действует форсажная камера?
11. Какие типы турбореактивных двигателей вы знаете?
12. К чему привело создание турбореактивных двигателей?
Задание 10. Переведите письменно текст.
Turbojet engines have been built in many sizes, ranging from a few hundred pounds of thrust to many thousand of pounds. The smaller engines are suitable for liaison – and training type aircraft, while the large engines are installed in high-performance fighter aircraft, bombers, transport, tankers, and commercial air liners.
The turbine supplies the power that drives the compressor: that is its main function in this type of engine.
In practice, this simple system is modified for various reasons. The more the pressure of the air is raised by the compressor, the higher the efficiency of the engine. Engines designed for the greatest economy have therefore tended towards higher compression ratios. This has led to splitting the compressor and turbine into two groups: a low-speed compressor driven by a low-speed turbine, and a separate high-speed compressor driven by a high-speed turbine, the two driving shafts being co-axial. This arrangement incorporates what is called a two-spool compressor.
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