Translate the following passage about internal combustion engine from Ukrainian into English.
Двигу́н вну́трішнього згоряння — тип двигуна, теплова машина, в якій хімічна енергія палива, що згоряє в робочій зоні, перетворюється в механічну роботу. Поряд з електричним двигуном двигун внутрішнього згоряння є одним із найпоширеніших типів двигунів. Найчастіше він використовується у транспортних засобах: автомобілях, мотоциклах, поїздах, авіації, водному транспорті тощо. Двигуни внутрішнього згоряння застосовуються також в автономних електричних генераторах для виробництва електроенергії.
Назва двигуна внутрішнього згоряння пов'язана з тим, що, на відміну від парової машини, горіння відбувається в закритій камері, в яку спеціально сконструйованими системами подається рідке або газоподібне паливо та повітря, кисень у складі якого виконує роль окисника. Гарячі гази, що утворюються при згорянні палива, створюють значний тиск, енергія якого перетворюється у механічну роботу.
У двигунах внутрішнього згоряння процеси згоряння палива, виділення теплоти й перетворення її в механічну енергію відбуваються безпосередньо у середині двигуна. До двигунів внутрішнього згоряння належать: поршневі та роторно-поршневі двигуни, газові турбіни і реактивні двигуни.
Найбільш економічними є поршневі двигуни внутрішнього згоряння. Основним недоліком цих двигунів є наявність кривошипно-шатунного механізму, що ускладнює конструкцію й обмежує можливість підвищення частоти обертання.
UNIT 5
GAS-TURBINE ENGINE
LEAD-IN
Try to give definitions of the following words which are used to talk about gas-turbine engines.
Internal-combustion engine, compressor, combustion chamber, turbine, reciprocating motion, rotary motion, piston, fuel. |
Look at the diagram and try to explain how the open-cycle constant-pressure gas-turbine engine works.
READING
Read the text and answer the questions that follow.
GAS-TURBINE ENGINE
Gas-turbine is any internal-combustion engine employing a gas as the working fluid used to turn a turbine. The term also is conventionally used to describe a complete internal-combustion engine consisting of at least a compressor, a combustion chamber, and a turbine.
Useful work or propulsive thrust can be obtained from a gas-turbine engine. It may drive a generator, pump, or propeller or, in the case of a pure jet aircraft engine, develop thrust by accelerating the turbine exhaust flow through a nozzle. Large amounts of power can be produced by such an engine that, for the same output, is much smaller and lighter than a reciprocating internal-combustion engine. Reciprocating engines depend on the up-and-down motion of a piston, which must then be converted to rotary motion by a crankshaft arrangement, whereas a gas turbine delivers rotary shaft power directly. Although conceptually the gas-turbine engine is a simple device, the components for an efficient unit must be carefully designed and manufactured from costly materials because of the high temperatures and stresses encountered during operation. Thus, gas-turbine engine installations are usually limited to large units where they become cost-effective.
IDEALIZED SIMPLE OPEN-CYCLE GAS-TURBINE ENGINE
Most gas turbines operate on an open cycle in which air is taken from the atmosphere, compressed in a centrifugal or axial-flow compressor, and then fed into a combustion chamber. Here, fuel is added and burned at an essentially constant pressure with a portion of the air. Additional compressed air, which is bypassed around the burning section and then mixed with the very hot combustion gases, is required to keep the combustion chamber exit (in effect, the turbine inlet) temperature low enough to allow the turbine to operate continuously. If the unit is to produce shaft power, the combustion products (mostly air) are expanded in the turbine to atmospheric pressure. Most of the turbine output is required to operate the compressor; only the remainder is available to supply shaft work to a generator, pump, or other device. In a jet engine the turbine is designed to provide just enough output to drive the compressor and auxiliary devices. The stream of gas then leaves the turbine at an intermediate pressure (above local atmospheric pressure) and is fed through a nozzle to produce thrust. A simplified schematic of a gas turbine engine is shown in Figure in exercise 2.
The efficiency of the gas-turbine cycle is limited by the need for continuous operation at high temperatures in the combustion chamber and early turbine stages. A small, simple-cycle gas turbine may have a relatively low thermodynamic efficiency, comparable to a conventional gasoline engine. Advances in heat-resistant materials, protective coatings, and cooling arrangements have made possible large units with simple-cycle efficiencies of 34 percent or higher.
In a combined-cycle power plant, the considerable heat remaining in the gas turbine exhaust is directed to a boiler called a heat-recovery steam generator. The heat so recovered is used to raise steam for an associated steam turbine. The combined output is approximately 50 percent greater than that of the gas turbine alone. Combined cycles with thermal efficiency of 52 percent and higher are being put into service. Gas turbines have been applied to the propulsion of ships and railroad locomotives. A modified form of gas turbine, the turbojet, is used for airplane propulsion. Heavy-duty gas turbines in both simple and combined cycles have become important for large-scale generation of electricity. Unit ratings in excess of 200 megawatts (MW) are available. The combined-cycle output can exceed 300 MW.
The usual fuels used in gas turbines are natural gas and liquids such as kerosene and diesel oil. Coal can be used after conversion to gas in a separate gasifier.
From Encyclopædia Britannica
1. What is a gas-turbine and what are its main components?
2. Why are gas-turbine engines much smaller and lighter than reciprocating internal-combustion engines?
3. Where is air fed at the beginning of the simple open cycle?
4. What happens after that?
5. What is the most of the turbine output spent for?
6. How efficient is the simple gas-turbine cycle?
7. Where is heat remaining in the gas turbine exhaust directed in a combined-cycle power plant?
8. What is the recovered heat used for?
9. Which is more efficient: a simple-cycle gas turbine or a combined-cycle power plant? Why?
10. Where are turbojets used?
11. What kind of fuels are used in gas turbines?
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