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Section 1. Main marine engines
Words and Terms to be Remembered
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powerplant |
output |
Read the text and find the answers to the following questions.
1. What main types of marine engine can be found at sea today?
2. Why must the propeller shaft rotate at a relatively slow speed?
3. What is the difference between steam and gas turbine?
4. Is the nuclear power used in merchant ships?
Ships are large, complex vehicles which must be self-sustaining in their environment for long periods with a high degree of reliability. A ship is the product of two main areas of skill, those of the naval architect and the marine engineer. The naval architect is concerned with the hull, its structure, form, habitability, and ability to endure its environment. The marine engineer is responsible for the various systems which propel and operate the ship. More specifically, this means the machinery required for propulsion, steering, anchoring and ship securing, cargo handling, air conditioning, power generation and its distribution.
There are four main types of marine engine: the diesel engine, the steam turbine, the gas turbine and the marine nuclear plant. Each type of engine has its own particular application.
A diesel engine is a ship's reciprocating machine, the internal combustion engine. To understand how a diesel engine works imagine the piston just near the top of its upstroke. All access from the outer air is closed but a given volume of air has been drawn in and trapped in between the bottom of the cylinder top and the top of the piston. Air is compressed and it heats. At the point of maximum compression a needle valve in the cylinder head opens, a spray of fuel enters. An explosion takes place and the piston is driven down the cylinder. Working via the piston rod, crosshead and connecting rod, it rotates the crankshaft. No diesel engine is a single cylinder engine, there may be as many as twelve driving one crankshaft, but each cylinder is self-sufficient in operation.
The diesel engine is started by means of compressed air admitted into the cylinder at high pressure via a special starting valve. There are two main types of diesel engines: one is the two-cycle and the other is the four-cycle. The power output of a modern marine diesel engine is about 40,000 brake horse power (bhp). This is now expressed in kilowatts. Large diesel engines, which have cylinders near 3 ft in diameter, turn at the relatively small speed of about 108 r.p.m. These are known as slow-speed diesel engines. They can be connected directly to the propeller without gearing. Although higher power could be produced by higher revolutions, this would reduce the efficiency of the propeller, because a propeller is more efficient the larger it is and the slower it turns. These large slow-running engines are used in the larger merchant ships, particularly in tankers and bulk carriers. The main reason is their low-fuel consumption.
More and more of the larger merchant vessels are being powered by medium-speed diesel engines. These operate between 150 and 450 r.p.m., therefore they are connected to the propeller by gearing. This type of engine was once restricted to smaller cargo ships, but now they are used in fast cargo liners as well as in tankers and bulk carriers.
The steam turbine has until recently been the first choice for very large power main propulsion units. Its advantages of little or no vibration, low weight, minimum space requirements and low maintenance costs are considerable. In steam turbines high pressure steam is directed into a series of blades or vanes attached to a shaft, causing it to rotate. This rotary motion is transferred to the propeller shaft by gears. Steam is produced by boiling water in a boiler, which is fired by oil. Recent developments in steam turbines which have reduced fuel consumption and raised power output have made them more attractive as an alternative to diesel power in ships. They are 50 per cent lighter and on very large tankers some of the steam can be used to drive the large cargo oil pumps. Turbines are often used in container ships, which travel at high speeds.
Gas turbines differ from steam turbines in that gas rather than steam is used to turn a shaft. These have also become more suitable for use in ships. Many naval vessels are powered by gas turbines and several container ships are fitted with them. A gas turbine engine is very light and easily removed for maintenance. It is also suitable for complete automation. The gas turbine efficiency being low, its main advantage is its small weight and size which makes a gas turbine installation very attractive for naval applications. Most of modern warships of about to 5,000 ton displacement are powered with gas turbines usually combined with diesel engines. Gas turbines are easier to start and reliable in operation. However, the use of astern gas turbines is a rather complex problem, therefore ships powered with main gas turbine units are equipped with either controllable pitch propellers (c.p.p.) or other reversing gears.
Nuclear power in ships has mainly been confined to naval vessels, particularly to submarines. But this form of power can be used more in merchant ships as oil fuels become more expensive. The atomic ice-breakers opened new possibilities in exploring the northern areas. They can sail for a long time without refueling. A nuclear-powered ship differs from a conventional turbine ship in that it uses the energy released by the decay of radioactive fuel to generate steam. The steam is used to turn a shaft via a turbine in the conventional way.
Exercises and assignments
Ex. 1. Give the other words of the same root for the words below. Find them in the text and translate the sentences in which they are used.
Remove, reciprocate, rotate, consume, reverse, explosion, combustion, efficiency, machine, application, attractive, alternative, explore, power, engine.
Ex. 2. Arrange the words below into the pairs of synonyms:
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restrict self-sustained output plant navy conventional combustion (to) power remove maintenance power reverse general explore |
produce drive energy traditional opposite service installation limit warships investigate burning independent take-off output |
Ex. 3. Translate the following word combinations using the maritime dictionary.
Output power, brake horse power, power propelled, reciprocating machine, main propelling machinery, single-acting engine, ship's electric power plant, emergency engine, non-reversible engine, combined diesel electric and gas turbine powerplant, geared engine, opposed-cylindrical engine, remote control engine, water cooled engine, two-stroke engine.
Ex. 4. Match the following words (terms) with their explanations.
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I |
II |
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1) force used for driving machines |
a) pitch |
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2) any powerful selfworking machine |
b) bed plate |
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3) any substance (e.g. oil), by which a fire is kept going |
c) turbine |
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4) a foundation framework for a marine engine |
d) power |
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5) the distance the propeller will advance during one revolution |
e) fuel |
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6) a screw with a set of blades |
f) nuclear reactor |
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7) a shaft turned by cranks which changes reciprocation motion into circular motion |
g) crankshaft |
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8) vapour from boiling water |
h) propeller |
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9) apparatus for producing atomic energy |
i) piston |
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10) machine or device for forcing liquid, gas or air into or out of or through smth |
j) pump |
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11) engine or motor whose driving wheel is turned by a flow of water, steam or gas |
k) shaft |
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12) the rod which turns the propeller |
l) steam |
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13) a connection by means of toothed wheels |
m) valve |
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14) a mechanical device for controlling the flow of air, gas, liquid in one direction |
n) gear |
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15) a cylinder fitting closely inside another cylinder used in engines, pumps to pass on motion |
o) engine |
Ex. 5. Read through the following paragraphs consulting the list of abbreviations in the Appendix.
· The newbuilding is powered by a Mitsubishi two-stroke diesel engine with an output of 14,160 kW driving a single 6.55 m diameter 5-bladed FP propeller. The service speed is about 20 knots. Auxiliary plant consists of three Daihatsu medium speed diesel gensets each producing 1,070 kW at 720 r.p.m. To help slow speed manoeuvring a 1,040 kW bow thruster is fitted.
· Unlike most of the large catamarans built to date, the HSS 900 is a twin jet vessel, one gas turbine is installed in each hull and its output of about 17 MW is fed to a single steerable and reversible KaMeWa waterjet. Auxiliary electric power will be generated by four 520 kW sets. The vessel can carry 104 m3 of fuel giving a range of 400 nautical miles at the anticipated fuel consumption at 100 per cent mcr of 10,700 litres per hour.
· The main engine is a single Sulzer 10RTA96C, supplied by Hyundai Heavy Industries, with an output of 54,900 kW (73,592 bhp) at an MCR of 100 rev/min. This is directly connected to a 8.4 m diameter Lips FP propeller. For operation in restricted waters the vessel is equipped with a Lips bow thruster of 2,000 kW.
Ex. 6. Translate into English.
Судовая энергетическая установка - это комплекс механизмов и устройств, предназначенных для обеспечения движения судна, а также для снабжения энергией различных механизмов, систем, устройств.
На судне имеется главный двигатель, который вырабатывает механическую энергию, потребляемую судовым движителем. На современных гражданских судах в качестве главных двигателей почти исключительно применяются дизели, т.е. двигатели внутреннего сгорания (ДВС), как наиболее экономичные, хотя сравнительно тяжелые и громоздкие. ДВС используют энергию газов, образующихся при сжигании топлива в двигателе или в специальном генераторе газа. К ним относятся дизели и газовые турбины. Паровые двигатели используют энергию пара, который образуется в паровых котлах при сжигании в них топлива. К ним относятся паровые машины и паровые турбины.
На подводных лодках, реже на надводных кораблях и гражданских судах, применяются атомные энергетические установки, использующие энергию деления атомов тяжелых элементов (уран) для получения пара, вращающего турбину. Встречаются комбинированные установки, например, дизель-газотурбинные. К судовым энергетическим установкам предъявляются требования экономичности, компактности, надежности, быстрой готовности к работе.