Download - Unit III Main Engine
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UNIT III
MACHINERY
MAIN ENGINE
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Steamengines were usedalmost
until 1900s. Laterthesteamturbineandthe
internal combustionengine
replacedsteamengines.
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Gasturbineshavebeen usedin
merchantshipsandnavy. Somesubmarines,merchantships,
andicebreakershavenuclearpower
plants.
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STEAM ENGINE
Thesteamengines convertheatenergyintomechanical
energyby usingsteam.
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Steamenginesoperatebyhaving
superheatedsteam forceapistontoreciprocateina cylinder.
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Thepistonisattachedbya
crossheadtoa crankshaftthat convertsthe
reciprocating (back-and-
forth) motionofthepistontorotarymotion forpropulsion.
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Inasteamengine,hotsteam
suppliedbyaboilerexpands under
pressure,andtheheatenergyis
convertedinto work.
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STEAM TURBINE
Inthesteamturbine,highpressure
steamisdischargedathighvelocitythroughnozzlesandthen flowsthrough
aseriesofstationaryandmoving
blades, causingarotortomoveathighspeeds.
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Steamturbinesaremore compactandusuallypermithighertemperaturesand
greaterexpansionratiosthansteam
engines.
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Theturbineis usedtogeneratelarge
quantitiesofelectric powerwithsteam.
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Nowadaysthesteamturbineis usedascargopumpdrivingsourceintankers.
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INT
ERNAL COMBUST
ION ENGINE
Aninternal combustion engine
operatesbyburningits fuelinsidetheengine.
It converts chemicalenergyofthe
burning fuelintomechanicalenergy.
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The commoninternal
combustionenginesare;
gasturbine
dieselengine
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The compressionignitedinternal
combustionenginehastwomaindesigns:
twostroke cycle
fourstroke cycle
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Thetwostrokeand fourstroke
termsrefertothemechanicalaction of the piston within the
cylinder.
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TWO STROKE CYCLE
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FOUR STROKE CYCLE
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DIES
EL ENGINE
Dieselengine usestheheatproducedby compressionto
ignitethemixtureofairand
diesel fuel.
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Dieselengineappearsinthreetypes, low-speedengine,
medium-speedengine
high-speedengine
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Thelow-speedengineis characterizedby
ratedspeedsintherangeof 0-400 rpm.
Itisatwo-strokeenginesuperchargedby
exhaust-gasturbochargers
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Themedium-speedenginerunsintherangeof4001000 rpm. Itisa four-
strokeenginesuperchargedby
exhaust-driventurbochargers.
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High-speedenginerunsintherange
of 1000-2000 rpm.
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Dieselenginesarealsooftwo
typesaccordingtotheirpistons;
trunkpiston
barrelpiston
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Dieselenginesareheavierthangasolineenginesbecauseoftheextra
strengthrequiredto containthehigher
temperaturesand compressionratios.
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The diesel engine differs from thegasoline engine in that the ignition of
fuel is caused by compression ofair in
its cylinders instead ofby a spark.
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The speed and power of the diesel arecontrolled by varying the amount of fuel
injected into the cylinder, not the amount of
air admitted as in the gasoline engine.
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GAS TURBINEGas turbine engines are extremely simple and
has three main parts;
a compressorto compress the incoming air tohigh pressure,
a combustion chamberto burn the fuel andproduce high pressure and
a turbine to extract the energy from the highpressure, high velocity gas flowing from thecombustion chamber
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The gas turbine is used as main propulsion
engine at naval ships and supertankers becauseofthe high power
but
it has low manoeuvring capability. Therefore, it
is combined with a diesel engine for highcapability ofmanoeuvring.
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ANSWER THE QUESTIONS
1-Whatarethemaintypesofengine?
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2-How doesaninternal combustionengine work?
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3-Whatdothetwostrokeand fourstroke
termsreferto?
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4-Canyou comparedieselengine withgasturbine?
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Etymology
Diesel
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SOME WORD
S
Combustion (n)- Burning
Expand (v) - Tobecomelargerinsize,
volumeorquantity
Ignite (v) - Starttoburnorburstinto flames
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Reciprocate (v) - Tomovebackand
forthRotary (n) - Occurringaroundanaxis
Rotate (v) - Turnaroundanaxis
Velocity (n) - Speed
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Complete the diagram showing
diesel engine types.
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B- Complete the definitions
using the words below.Internal combustion engine / boiler / compressor / crankshaft /
diesel engine
1-A.isadevicethatsupplieshotsteam forsteamengine.
2-A isadevicethat convertstheback-and-forthmotionofthepistontorotarymotion forpropulsion
3- isanenginetypethat converts chemicalenergyoftheburning fuelintomechanicalenergy.
4-A isanenginethat usestheheatproducedbycompression.
5-A.isadevicethat compressestheincomingairtohighpressure
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1-What statement is not true
regarding the steam engines?
a. Steamengines usessteam.
b. Steamengines convertheatenergyinto work.
c. Pistonrotatesina cylinderto
reciprocatethe crankshaft
d. Boilerssupplyhotsteam.
e. Steamenginesarenot common.
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1-What statement is not true
regarding the steam engines?
c. Pistonrotatesina cylinderto
reciprocatethe crankshaft
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1-Which one is used for
propulsion on ships?
a. steamengineb. steamturbine
c.gasturbine
d.dieselenginee.all
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1-Which one is used for
propulsion on ships?
e.all
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3-combustion, compression,
stroke. The terms are related to
a. steamturbine
b. turbine
c. boiler
d. internal combustionenginee. reciprocatingsteamengine
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3-combustion, compression,
stroke. The terms are related to
d. internal combustionengine
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4-What does the term
stroke refer to?
a. combustion
b. pistonmotioninthe cylinder
c. ignition
d. compressione. rotarymotion
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4-What does the term
stroke refer to?
b. pistonmotioninthe cylinder
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5-Which is not a characteristic
of diesel engines?
a. Dieselengines canbeeithertrunkpistontypeor
barrelpistontype.
b. Theignitionis causedbysparkc. Theyareheavierthangasturbines.
d. Thepoweris controlledbyvaryingtheamountof
injected fuel.
e. Dieselenginesoperateatvariousspeedssuch
aslow,mediumorhigh.
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5-Which is not a characteristic
of diesel engines?
b. Theignitionis causedbyspark
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6-Which is not true about
gas turbines?a. Gasturbineshavehighmaneuvering
capability
b. They consistof compressor,turbineandcombustion chamber
c. Theyarelighterthandieselengines
d. Theirignitionis causedbysparke. Theyare usedatnavalshipsand
supertankers.
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6-Which is not true about
gas turbines?
a. Gasturbineshavehighmaneuvering
capability
.
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7-Which is the most common
propulsion engine for merchant
ships?
a. steamengine
b. steamturbine
c. gasturbine
d. nuclearpowere. dieselengine
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7-Which is the most common
propulsion engine for merchant
ships?
e. dieselengine