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Файл:Jet Propulsion Engine Fundamentals английский язык для студентов специальности «Проектирование авиационных и ракетных двигателей». Учебное пособие
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The gas generator mixture ratio is usually
fuel or oxidizer rich …
through one or two separate small lowarea-ratio nozzles (at relatively low
specific impulse).
In closed cycles all the working fluid
from the turbine is injected …
and sometimes reduces the hardware
mass, volume, and cost.
An arrangement with the fuel and
oxidizer pump driven by the same turbine
is also feasible …
the specific propellant flow paths through
the major engine components, the method
of providing the hot gas to one or more
turbines, and the method of handling the
turbine exhaust gases.
Engines with turbopumps are preferred
for booster and sustainer stages of space
launch vehicles, long-range missiles, …
directly by the jet engine.
Typically, the turbine exhaust gas is
discharged overboard …
so that the gas temperatures are low
enough to allow the use of uncooled
turbine blades and uncooled nozzle exit
segments.
For aircraft performance augmentation
the rocket pump can be driven …
and in the past for aircraft performance
augmentation.
Task 11. Read the following text and try to understand its subject matter.
Translate the text into Russian. Use the dictionary if necessary.
TURBOPUMP FEED SYSTEMS AND ENGINE CYCLES
In the expander cycle most of the engine coolant (usually hydrogen fuel) is fed to
low-pressure-ratio turbines (турбины с низкой степенью сжатия) after having
passed through the cooling jacket where it picked up energy. Part of the coolant,
perhaps 5 to 15%, bypasses the turbine and rejoins the turbine exhaust flow before
the entire coolant flow is injected into the engine combustion chamber where it mixes
and burns with the oxidizer. The primary advantages of the expander cycle are good
specific impulse, engine simplicity, and relatively low engine mass. In the expander
cycle all the propellants are fully burned in the engine combustion chamber and
expanded efficiently in the engine exhaust nozzle. This cycle is used in the RL10
hydrogen/oxygen rocket engine, and different versions of this engine have flown
successfully in the upper stages of several space launch vehicles. A recent
modification of RL10-A3-3A, the RL10B-2 with an extendible nozzle skirt
(сопловой насадок) delivers the highest specific impulse of any chemical rocket
engine to date. Heat absorbed by the thrust chamber cooling jacket gasifies and raises
the gas temperature of the hydrogen so that it can be used to drive the turbine, which
(Part 2)
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in turn drives a single-stage (одноступенчатый) liquid oxygen pump (насос для
подачи жидкого кислорода) (through a gear case (редуктор)) and a two-stage
liquid hydrogen pump. The cooling down of the hardware to cryogenic temperatures
is accomplished by flowing (prior to engine start) cold propellant through cooldown
valves (клапаны системы охлаждения). Thrust is regulated by controlling the flow
of hydrogen gas to the turbine, using a bypass (параллельный контур) to maintain
constant chamber pressure. Helium is used as a means of power boost
(форсирование наддува) by actuating several of the larger valves through solenoid-
operated pilot valves (клапан с электромагнитным управлением (соленоидный
клапан)).
In the staged combustion cycle, the coolant flow path through the cooling jacket is
the same as that of the expander cycle. Here a high-pressure precombustor
(предтопок) (gas generator) burns all the fuel with part of the oxidizer to provide
high-energy gas to the turbines. The total turbine exhaust gas flow is injected into the
main combustion chamber where it burns with the remaining oxidizer. This cycle
lends itself to high-chamber-pressure operation, which allows a small thrust chamber
size. The extra pressure drop in the precombustor and turbines causes the pump
discharge pressures (давление нагнетания насоса) of both the fuel and the oxidizer
to be higher than with open cycles, requiring heavier and more complex pumps,
turbines, and piping. The turbine flow is relatively high and the turbine pressure drop
is low, when compared to an open cycle. The staged combustion cycle gives the
highest specific impulse, but it is more complex and heavy.
In contrast, an open cycle can allow a relatively simple engine, lower pressures,
and can have a lower production cost. A variation of the staged combustion cycle is
used in the Space Shuttle main engine. This engine actually uses two separate
precombustion chambers, each mounted directly on a separate main turbopump. In
addition, there are two more turbopumps for providing a boost pressure (давление
подкачки) to the main pumps, but their turbines are not driven by combustion gases;
instead, high-pressure liquid oxygen drives one booster pump (бустер-помпа) and
evaporated hydrogen drives the other. While the space shuttle main engine
(главный/маршевый двигатель) (burning hydrogen with oxygen) has fuel-rich
preburners (газогенераторные камеры), oxidizer-rich preburners are used in the
RD120 engine (kerosene/oxygen) and other Russian rocket engines. Another example
of a staged combustion cycle is the Russian engine RD253; all of the nitrogen
tetroxide oxidizer and some of the unsymmetrical dimethyl hydrazine fuel are burned
in the precombustor, and the remaining fuel is injected directly into the main
(основной) combustion chamber.
(Sutton, George P. & Biblarz, Oscar Rocket Propulsion Elements: an introduction to
the engineering of rockets)
Task 12. Answer the questions and use them as a plan for retelling the text.
1. When is most of the engine coolant fed to low-pressure-ratio turbines in the
expander cycle?
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2. What are the primary advantages of the expander cycle?
3. What part of the propellants is fully burned in the engine combustion chamber?
4. Where is the expander cycle used?
5. What are the main operational features of the expander cycle?
6. What differentiates the staged combustion cycle from the expander cycle?
7. What are the advantages and limitations of the staged combustion cycle?
8. What specifies the Space Shuttle main engine?
9. What differs the Space Shuttle main engine from RD120 and RD253?
Task 13. Translate the following sentences into English.
1. В ракетных двигателях с турбонасосной системой подачи топлива
мощность турбины обеспечивается за счет расширения горячих газов.
2. В двигателях с турбонасосной системой подачи топлива цикл двигателя
характеризует расчетную траекторию топливного потока через основные узлы
двигателя, метод подачи горячего газа на одну или несколько турбин, а также
метод удаления отработавших в турбине газов.
3. В открытом цикле рабочее тело после расширения в сопле турбины
истекает из турбины и удаляется за борт или в сопло камеры сгорания гораздо
ниже горла сопла.
4. В замкнутом цикле рабочее тело нагнетается в камеру сгорания
двигателя, а отработавший в турбине газ расширяется, используя всю степень
расширения сопла основной камеры сгорания.
5. Как в открытой, так и в замкнутой схеме ЖРД можно использовать
большинство распространенных видов жидкого ракетного топлива, тогда как в
безгенераторной схеме ЖРД в качестве хладагента камеры сгорания
предпочтительнее использовать криогенный водород в газообразном
состоянии, обладающий отличной теплопоглощающей способностью и не
разлагаемый на составные элементы.
6. В газогенераторном цикле газ на вход в турбину подается из отдельного
газогенератора и, отработав в турбине, удаляется за борт через одно или два
отдельных небольших сопла с малой степенью уширения.
7. Соотношение компонентов топлива для газогенератора обычно
характеризуется избытком горючего, поэтому газ имеет достаточно низкую
температуру, что позволяет использовать неохлаждаемые лопасти турбины и
сегменты выходной части сопла.
8. В безгенераторной схеме ЖРД компоненты топлива полностью сгорают в
камере сгорания и эффективно расширяются в выхлопном сопле двигателя.
9. В замкнутой схеме ЖРД весь поток выхлопных газов из турбины
нагнетается в основную камеру сгорания, где он сгорает с оставшимся
окислителем.
10. Регулирование тяги происходит посредством управления идущим в
турбину потоком водорода в газообразном состоянии, используя параллельный
контур для обеспечения постоянного давления в камере.
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Task 14. Find the Russian equivalents for the English terms.
1. nozzle skirt
2. bypass
3. staged combustion cycle
4. coolant
5. booster pump
6. specific impulse
7. main engine
8. expander cycle
9. oxidizer/fuel-rich
10. working fluid
11. solenoid-operated pilot valve
12. preburner
13. a single-stage liquid oxygen pump
14. gas generator cycle
15. low-pressure-ratio turbines
16. mixture ratio
17. specific propellant flow paths
18. power boost
19. precombustor
20. exhaust flow
21. low-area-ratio nozzle
22. turbopump
23. a two-stage liquid hydrogen pump
24. turbine blade
25. nozzle throat
26. engine exhaust nozzle
27. boost pressure
28. cooldown valve
29. pump discharge pressure
30. cooling jacket
1. одноступенчатый насос для подачи
жидкого кислорода
2. поток выхлопных газов
3. расчетная траектория топливного
потока
4. предтопок
5. открытая схема ЖРД
6. турбины с низкой степенью сжатия
7. турбонасос
8. двухступенчатый насос для подачи
жидкого водорода
9. сопло с малой степенью уширения
10. замкнутая схема ЖРД
11. соотношение компонентов топлива
12. клапан системы охлаждения
13. лопатка турбины
14. выхлопное сопло двигателя
15. параллельный контур
16. бустер-помпа
17. давление нагнетания насоса
18. сопловой насадок
19. давление подкачки
20. охлаждающая рубашка
21. рабочее тело
22. горло сопла
23. форсирование наддува
24. избыток окислителя (топлива)
25. маршевый двигатель
26. удельный импульс
27. газогенераторная камера
28. хладагент
29. соленоидный клапан
30. безгенераторная схема ЖРД
Task 15. Look through the texts (Task 7, 11) and find key sentences in each
paragraph.
Task 16. Write a summary to the text (Task 7)
Task 17. Sum up the text (Task 11).
Task 18. Skim the text and try to understand its subject matter.
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Propellant Pumps
The principal requirements of a rocket-engine propellant pump are high
reliability, low cost, light weight, stable flow for the required operating range, high
efficiency, adequate suction performance, and long life. The relative importance of
these factors and their resulting influence on the design will vary depending on the
application. The most widely used pump types are centrifugal (or radial), axial, or
mixed flow. Centrifugal pumps are usually designed with a single stage; axial pumps,
multistage. However, multistage centrifugal pumps with crossover-type diffusion
systems have also been used effectively.
Centrifugal pumps. Almost all operational rocket propellant pumps are of this
type. They can handle large flows at high pressures efficiently as well as
economically in terms of weight and size. Centrifugal pumps, like other steady-flow
rotating machinery, consist essentially of two basic elements: the rotor and the stator.
These accelerate the fluid flow by imparting kinetic energy to it in the rotor and then
decelerating, or ‘diffusing’, it in the stator. This results in increased fluid pressure
head. The rotor assembly usually includes an inducer, an impeller, bearings, and a
shaft. The stator assembly consists of a casing with stationary diffuser vanes, a volute
with discharge outlet, and seals. An inducer, an axial-flow rotor, increases total
pressure of the entering fluid sufficiently to permit noncavitating operation of the
main impeller.
An inducer can reduce the pump-inlet-pressure net positive suction head (NPSH)
requirements substantially. The impeller of a centrifugal (or radial) pump basically is
a rotating wheel with blades that discharge the flow in a radial direction. Fluid is
admitted axially to the impeller that, when rotating in an enclosure, ejects it at the
periphery with increased absolute velocity.
As primary functions, the pump stator assembly diffuses (i.e., decelerates) the
fluid to convert the velocity head into pressure head, collecting and redirecting the
fluid to the pump discharge outlet, and provides structural support and a pressure
enclosure for the pump. Wear rings provide axial-thrust control and minimize internal
leakage--circulation of the fluid between the high-pressure (discharge) and the lowpressure (inlet or suction) zones. Dynamic shaft seals prevent external leakage along
the shaft.
Multistage centrifugal pumps. For higher pressure rises, multiple-stage
centrifugal pumps can be designed if a single stage proves limited. A multistage
pump basically resembles a single-stage pump, except that it requires proper
channeling of the fluid between stages.
Multistage axial pumps. This design permits achieving high head through
multiple staging with smaller-diameter pumps. It has been used for liquid-hydrogen
pump applications. It is not as well suited for wide-flow-range operation, but can be
more efficient in applications requiring relatively high ratios of flow vs. head (or at
high ‘specific speeds’). The rotor assembly consists of an inducer, a cylindrical rotor
with multiple rows of rotating blades, and a rotor shaft. The stator assembly includes
a cylindrical casing with rows of stationary blades spaced between inducer and
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rotating blades, a volute casing, beatings, and seals.
An inducer placed at the pump inlet supplies the fluid to the main-pump section at
the required pressure and velocity. Both rotor and stator blades have a hydrofoil
shape. The rotor blades accelerate the flow relative to the stator and thus increase the
kinetic energy of the fluid, while the stator blades, acting as diffusers, convert the
velocity head of the fluid into pressure head. However, the velocity vector of the fluid
in the axial direction is kept essentially constant throughout the various stages of the
pump.
Inducer pumps. The simplest axial-flow pump consists of a single rotor designed
as an inducer to achieve good suction. The inducer can consist of either a single- or
double-blade row. These pumps are used as low-speed "boost pumps" to raise the
pressure sufficiently to permit the main pump to operate at much higher speeds to
reduce its size and cost. The inducer design for this pump is similar to those used in
either centrifugal- or axial-flow pumps.
(Huzel, Dieter K. and Huang, David H. Modern Engineering for Design of Liquid-
Propellant Rocket Engines.)
Task 19. Choose the right variant to fill in the gap.
1. The most widely used pump types are __________and__________.
a) axial, inducer
b) centrifugal, inducer
c) centrifugal, axial
2. Almost all operational rocket propellant pumps are of ___________ type.
a) axial
b) inducer
c) centrifugal
3. Centrifugal pumps consist essentially of____________.
a) the rotor
b) the rotor and the stator
c) the stator
4. ___________increases total pressure of the entering fluid sufficiently to permit
noncavitating operation of___________.
a) an inducer, the main impeller
b) an inducer, the rotor
c) the rotor, the shaft
5. The impeller of a centrifugal pump basically is a __________wheel with blades
that discharge the flow in a radial direction.
a) fixed
b) rotating
c) stationary
6. Dynamic shaft seals prevent external ___________ along the shaft.
a) suction
b) friction
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c) leakage
7. A multistage pump requires proper channeling of __________ between stages.
a) the fluid
b) the mixture
c) the liquids
8. In a multistage axial pump, an inducer placed at the pump inlet supplies the
fluid to the main-pump section at the required___________.
a) pressure and temperature
b) pressure and velocity
c) temperature and velocity
9. The simplest axial-flow pump consists of a single rotor designed as
__________to achieve good suction.
a) an inducer
b) a cylindrical rotor
c) a diffusor
10. The impeller of a centrifugal pump basically is a rotating wheel with blades
that discharge the flow in a ___________ direction.
a) radial
b) axial
c) straight
Task 20. Collect all the possible supplementary information on the theme of Unit
8 and present it to your groupmates.
SUPPLEMENTARY READING
Text 1
Task 1. Read and translate the text
Structure and operation of the engine
The engine is the source of power that makes the wheels go around and the car move.
It is usually referred to as an internal-combustion engine because gasoline is burned
within its cylinders or combustion chambers. This burning, or combustion, takes
place at such high speed as to be termed an "explosion"; the high pressure thus
created causes a shaft to turn or rotate. This rotary motion is transmitted to the car
wheels by the power train.
Most automobile engines have six or eight cylinders, although some four-, twelve-,
and sixteen-cylinder engines are in use.
Engine Operation. The activities that take place in the engine cylinder can be
divided into four stages, or strokes. ‘Stroke’ refers to the piston movement. The upper
limit of piston movement is called top dead center, or T. D. C. The lower limit of
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piston movement is called bottom dead centre or B. D. C. A stroke constitutes piston
movement from TDC to BDC or from BDC to TDC. In other words, the piston
completes a stroke each time it changes direction of motion. Where the entire cycle of
events in the cylinder requires four strokes (two crankshaft revolutions), the engine is
called a four-stroke-cycle engine. The four strokes are: intake, compression, power
and exhaust.
Intake. On the intake stroke the intake valve is opened. The piston is moving down,
and a mixture of air and vaporized gasoline is being drawn into the cylinder through
the valve opening. The mixture of gasoline and air is delivered to the cylinder by the
fuel system.
Compression. After the piston reaches BDC it begins to move upward and at this
instant the intake valve closes. The other valve is also closed so that the cylinder is
sealed. The piston moves upward, compressing the mixture to as little as one sixth of
its original volume or less. This creates a fairly high pressure within the cylinder.
Power. As the piston reaches TDC or the upper limit of its travel, an electric spark is
generated at the cylinder spark plug. The spark plug consists of two electrodes, which
are electrically insulated from each other. At the proper instant the ignition system
delivers a high-voltage surge of electricity to the spark plug. This causes an electric
spark to jump across the gap between the spark plug electrodes. The spark ignites or
sets fire to the highly explosive mixture of gasoline vapor and air. Rapid combustion
takes place, and the already high pressure within the cylinder increases to as much as
400 pounds per square inch. This terrific pressure against the top of the piston forces
it downward, and a power impulse is transmitted to the engine crankshaft through the
connecting rod and crank.
Exhaust. As the piston reaches the lower limit of its travel again, the exhaust valve
opens. The piston moves upward on the exhaust stroke, forcing the burned gases out
of the cylinder through the exhaust-valve opening. At the instant that the piston once
more reaches top dead center, the exhaust valve closes and the intake valve opens so
that, when the piston begins to move downward on the intake stroke, a fresh charge
of gasoline vapor and air can be drawn into the cylinder. The above four strokes are
continually repeated during the operation on the engine.
Task 2. Put the sentences in order they appear in the text.
1. The piston completes a stroke each time it changes direction of motion.
2. At the instant that the piston once more reaches top dead center, the exhaust
valve closes and the intake valve opens.
3. The mixture of gasoline and air is delivered to the cylinder by the fuel system.
4. At the proper instant the ignition system delivers a high-voltage surge of
electricity to the spark plug.
5. The piston moves upward on the exhaust stroke, forcing the burned gases out
of the cylinder through the exhaust-valve opening.
88
6. The spark ignites or sets fire to the highly explosive mixture of gasoline vapor
and air.
7. Most automobile engines have six or eight cylinders, although some four-,
twelve-, and sixteen-cylinder engines are in use.
8. ‘Stroke’ refers to the piston movement.
9. The four strokes are: intake, compression, power and exhaust.
10. The piston moves upward, compressing the mixture to as little as one
sixth of its original volume or less.
Text 2
Task 1. Read and translate the text
Fuel System
The fuel system is designed to store liquid gasoline and to deliver it to the engine
cylinders on the intake strokes in the form of vapor mixed with air. The fuel system
must vary the proportions of air and gasoline vapor to meet the requirements of the
various operating conditions. Thus for initial starting with a cold engine a very rich
mixture of about 9 pounds of air to 1 pound of gasoline is needed. After the engine
has warmed up, it will run satisfactorily on a leaner mixture of about 15 pounds of air
for each pound of gasoline. For acceleration and full-load, the mixture must again be
enriched.
The fuel system consists of a tank in which the liquid gasoline is stored, a fuel line, or
tube, through which the gasoline can be brought from the tank to the engine, a pump,
which pulls the gasoline through the fuel line, and a carburetor, which mixes the
gasoline with air.
Fuel Pump. The fuel pump consists of a rocker arm, a flexible diaphragm, and two
valves. The rocker arm rests against a cam on the camshaft so that rotation of the
shaft makes the arm rock. This rocking motion causes the diaphragm to fluctuate up
and down, alternately creating pressure and vacuum in the pump chamber. When
vacuum is created, the inlet valve is lifted off its seat, allowing gasoline to be drawn
from the fuel tank, through the fuel line, and into the pump chamber. On the return
stroke the diaphragm creates pressure in the pump chamber. This causes the inlet
valve to close and the outlet valve to open, forcing gasoline from the pump chamber
through a fuel line to the carburetor.
Fuel Tank. The fuel tank, normally located at the rear of the vehicle and attached to
the frame, is merely a storage tank made of sheet metal. It often contains a number of
metal plates, which are attached to the inner surface of the tank parallel to the ends.
These have openings through which the gasoline can pass, and their main purpose is
to prevent sudden surging of the gasoline from one to the other end of the tank, when
the car rounds a corner.
Power Train. The power that the engine develops must be transmitted to the car
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wheels, so that the wheels will rotate and cause the car to move. The power train
performs this job, providing in the process several different gear ratios between the
engine crankshaft and wheels, so that the engine crankshaft may rotate approximately
four, eight, or twelve times to cause the wheels to rotate once. The power train
consists of a series of gears and shafts, which mechanically connect the engine shaft
with the car wheels, and contains a clutch, a transmission or change gears, a propeller
shaft, and the final drive.
Clutch. The clutch permits the driver to connect the crankshaft to or disconnect it
from the power train. A clutch is necessary since the automobile engine must be
started without load. In order for the engine to deliver power, the crankshaft must be
rotating at a reasonable speed of several hundred revolutions per minute or more. The
engine will start at speeds below 100 r.p.m. (revolutions per minute), but it would not
continue to operate at this low speed if a load were immediately thrown on it.
Consequently, a clutch is placed in the power train between the crankshaft and
transmission. The clutch permits the engine to run freely without delivering power to
the power train. It also permits operation of the transmission so that the various gear
ratios between the engine crankshaft and wheels may be obtained.
Text 3
Task 1. Read and translate the text
Chemical Rocket Engines (RHD)
Rocket engines in essence are ordinary jet engines with one important feature:
they do not use atmospheric oxygen as a fuel oxidizer to create jet thrust. Everything
that is needed for its operation is located either directly in its housing or in the
oxidizer and fuel supply systems. It is this feature that makes it possible to use rocket
engines in outer space.
There are a lot of types of rocket engines and all of them are strikingly different
from each other not only by design features, but also by the principle of operation.
That is why each species must be considered separately.
Among the main operating characteristics of rocket engines, special attention is
paid to the specific impulse - the ratio of the amount of reactive thrust to the mass of
the working fluid consumed per unit time. The specific impulse value reflects the
efficiency and economy of the engine.
Today, RHD is the only one that is massively used to launch spacecraft into
outer space; in addition, it has found application in the military industry. Chemical
engines are divided into solid and liquid fuel depending on the state of aggregation of
rocket fuel.
History of creation. The first rocket engines were solid fuel, and they appeared
several centuries ago in China. Little was connected to space then, but with their help
it was possible to launch military rockets. As fuel, a powder was used that resembled
gunpowder in composition, only the percentage of its components was changed. As a
result, during oxidation, the powder did not explode, but gradually burned out,
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