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Text 3. Gas Turbines
A gas turbine is a machine which has a single-stage centrifugal compressor, turbine, a recuperator and foil bearings. A gas turbine extracts energy from a flow of hot gas produced by combustion of gas or fuel oil in a stream of compressed air. It has an upstream air compressor (radial or axial flow) mechanically coupled to a downstream turbine and a combustion chamber. “Gas turbine” may also refer to just the turbine element. Energy is released when compressed air is mixed with fuel and ignited in the combustion chamber. The resulting gases are directed over the turbine blades, spinning the turbine and mechanically powering the compressor. Finally, the gases are passed through a nozzle, generating additional thrust by accelerating the hot exhaust gases by expansion back to atmospheric pressure.
Energy is extracted in the form of shaft power, compressed air and thrust in any combination and used to power aircraft, trains, ships, electrical generators, and even tanks.
With all cyclic heat engines, higher combustion temperature means greater efficiency. The limiting factor is the ability of the steel, nickel, ceramic or other materials that make up the engine to withstand heat and pressure. Considerable engineering goes into keeping the turbine parts cool. Most turbines also try to recover exhaust heat, which otherwise is wasted energy. Recuperators are heat exchangers that pass exhaust heat to the compressed air prior to combustion. Combined cycle designs pass waste heat to steam turbine systems. A co-generation of heat and power uses waste heat for hot water production.
Mechanically, gas turbines can be considerably less complex than internal combustion piston engines. Simple turbines might have one moving part: the shaft, compressor, turbine, alternative rotor assembly not counting the fuel system.
More sophisticated turbines (such as those found in modern jet engines) may have multiple shafts, hundreds of turbine blades, movable stator blades, a vast system of complex piping, combustors and heat exchangers.
Thrust bearings and journal bearings are a critical part of design. Traditionally they have been hydrodynamic oil bearings or oil-cooled ball bearings. This is giving way to foil bearings, which have been successfully used in micro turbines and auxiliary power units.
Jet engines are gas turbines optimized to produce thrust from the exhaust gases or from ducted fans connected to the gas turbines. Jet engines that produce thrust primarily from the direct impulse of exhaust gases are often called turbojets. Jet engines that generate most of their thrust from the action of a ducted fan are often called turbofans or (rarely) fanjets.
Auxiliary power units (APUs) are small gas turbines designed for auxiliary power of larger machines, such as those inside an aircraft. They supply compressed air for aircraft ventilation (with an appropriate compressor design), start-up power for larger jet engines, electrical and hydraulic power.
Exercise 22. Answer the questions on text 3.
1. What is a gas turbine?
2. What is the purpose of a gas turbine?
3. When is energy released?
4. How is the compressor powered?
5. How is additional thrust produced?
6. What kind of energy is used to power aircraft, trains, ships, electrical generators, tanks?
7. Why are cyclic heat engines more efficient?
8. How does the engine withstand heat and pressure?
9. What is the purpose of a recuperator?
10. What is used for hot water production?
11. How are more sophisticated turbines designed in comparison with simple turbines?
12. What is a critical part of a turbine design?
13. What is called jet engines?
14. What jet engines are called turbojets?
15. What jet engines are called turbofans?
16. What are auxiliary power units designed for?
Exercise 23. Say whether the given statements are true or false. If a statement is wrong, correct. If true, enrich it with details.
1. Gas turbine may refer to just the turbine element.
2. Higher combustion temperature means less efficiency.
3. The engine is made up of steel, nickel, ceramic and the materials to withstand heat and pressure.
4. Nozzles pass exhaust heat to the compressed air prior to combustion.
5. Gas turbines can be considerably more complex than internal combustion engines.
6. Turbojets produce thrust from the action of a ducted fan.
7. Auxiliary power units supply compressed air for aircraft ventilation, start-up power for larger jet engines.
Exercise 24. Memorize the following words and word combinations to text 4.
Match – відповідати (вимогам), підходити
gearbox – редуктор, коробка передач
frequency – частота; частотність; повторюваність
power grid – електромережа
avoid – уникати
dedicated enclosure – відповідне огородження/огороджена територія
base load power plant – електростанція зі статичним (основним) навантаженням
advantage – перевага
peak demand – період найвищого попиту
generating capacity – виробничі потужності
shortage – скорочення
load – навантаження
cycle – цикл, круговий процес
train – зубчата передача
liquefaction – зжиження
favour – віддавати перевагу
power-to weight ratio - потужність на одиницю ваги (двигуна)
road vehicle – автотранспорт
performance – технічна характеристика; технологічність
resist – протистояти, протидіяти
regardless of – незалежно від, не дивлячись на, не приймаючи до уваги
unless – якщо не, поки не
Exercise 25. Read, translate and give the gist of text 4.