Передмова (стр. 31 )

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 bined 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 – відповідна огорожа / 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 – зрідження

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.

Text 4. Industrial Gas Turbines

Gas turbines are widely used in industry for electrical power production. Industrial gas turbines range in size from truck-mounted mobile plants to enormous complex systems. They can be particularly efficient up to 60%, when waste heat from the gas turbines is recovered by a heat recovery steam generator to power a conventional steam turbine in a combined cycle configuration. They can also be used for space or water heating, cooling or refrigeration. The power turbines in the largest industrial gas turbines operate at 3,000 or 3,600 rpm to match the AC power grid frequency and to avoid the need for a reduction ch engines require a dedicated enclosure. Simple cycle gas turbines in the power industry require smaller capital investment than either coal or nuclear power plants and can generate small or large amounts of power. Also, the actual construction process can take as little as several weeks to a few months, compared to years for base load power plants. Their other main advantage is the ability to be turned on and off within minutes, supplying power during peak demand. Since they are less efficient than combined cycle plants, they are usually used as peaking power plants, which operate anywhere from several hours per day to a couple dozen hours per year, depending on the electricity demand and the generating capacity of the region. In areas with a shortage of base load and load following power plant capacity a gas turbine power plant may regularly operate during most hours of the day and even into the evening. A typical large simple cycle gas turbine may produce 100 to 300 megawatts of power and have 35-40 % thermal efficiency. The most efficient turbines have reached 46 % efficiency.

Turboshaft engines are often used to drive compression trains (for example in gas pumping stations or natural gas liquefaction plants) and are used to power almost all modern helicopters.

Gas turbine engines have some essential advantages:

-  very high power-to-weight ratio, compared to reciprocating engines (i. e. most road vehicle engines);

-  smaller than most reciprocating engines of the same power rating;

-  moves in one direction only, with far less vibration than a reciprocating engine, so very reliable;

-  simpler design;

-  low operating pressures;

-  high operation speeds;

-  low lubricating oil cost and consumption.

Gas turbine engines also have some disadvantages:

-  cost is much greater than for a similar-sized reciprocating engine (very high-performance, strong, heat-resistant materials needed);

-  use more fuel when compared to reciprocating engines and not so good unless in continual operation.

These disadvantages explain why road vehicles, which are smaller, cheaper and follow a less regular pattern of use than tanks, helicopters, large boats and so on, do not use gas turbine engines regardless of the size and power advantages.

Exercise 26. Translate the following universal words. Mind the difference in pronunciation and meanings in English and Ukrainian.

Mechanically, extract, atmospheric, form, combination, cycle, temperature, limit, factor, material, system, complex, maximum, micro, critical, optimize, ventilation, hydraulic, megawatt, configuration, mobile, refrigeration, reduction, investment, construction, process, base, minute, peak, region, typical, modern, prototype, stress, aerodynamic, optimal, radial, tank, optimal, integrity.

Exercise 27. Determine the parts of speech of the following words. Explain their grammar forms, name the affixes, if any, and translate.

Smaller, cheaper, less, regardless, single-stage, recuperator, expansion, atmospheric, pressure, thermodynamically, higher, withstand, might, hydraudynamic, oil-cooled, successfully, largely, largest, enormous, conventional, enclosure, several, anywhere, turboshaft, shortage, most, efficient, almost, all, both, well, thinner, power-to-weight, same, far, simpler, high-performance, heat-resistant, similar-sized, unless, gearbox, upstream, downstream, start-up, continual.

Exercise 28. Match the English terms in the left column with their Ukrainian equivalents in the right column.

1)  ball bearing 2)  piston 3)  ducted fan 4)  gearbox 5)  turbojets 6)  combustion chamber 7)  heat exchanger 8)  housing 9)  journal bearing 10)  thrust bearing

a)  редуктор b)  корпус c)  упорний підшипник d)  поршень e)  тяговий вентилятор f)  радіальний підшипник g)  камера згоряння h)  кульковий підшипник i)  теплообмінник j)  турбореактивні двигуни

Exercise 29. Translate the following attributive word combinations.

1) n + n:

single-stage compressor, gas turbines, fuel oil, air compressor, downstream turbine, combustion chamber, turbine blade, shaft power, heat engine, combustion temperature, heat exchanger, piston engine, rotor assembly, fuel system, thrust bearing, rotation rate, oil bearing, ball bearing, foil bearing, power plant, reduction gearbox, turboshaft engine, can combustion system, pressure ratio, diffuser exit, rotor suspension, power demand, power grid, rotor support, generator speed requirements.