Lesson one Text How does a Marine Diesel engine Work?The diesel engi
ne is a type of internal combustion engine which ignites(点燃) the
fuel by injecting(喷射) it into hot, high pressure air in a combust
ion chamber(燃烧室). The marine diesel engine is a type of diesel en
gine used on ships. The principle of its operation is as follows:
A charge(装、充气) of fresh air is drawn or pumped into the engine cy
linder and then compressed by the moving piston(活塞) to very high
pressure.When the air is compressed, its temperature rises so tha
t it ignites the fine(细小的) spray(喷雾、油雾) of fuel injected into the
cylinder.The burning of the fuel adds more heat to the air charg
e, causing it to expand and force the engine piston to do work on
the crankshaft which in turn (依次，按次序，顺序地) drives the ship’s prop
eller.Exhaust valveInlet valveFuel injectorCylinderPistonPiston r
ingConnecting rodFour-stroke diesel engineCombustion chamberPisto
n pincrankshaftCrank webFuel injectorFuel injectorExhaust valveSc
avenge portExhaust portTwo-strokeEngineLoop scavenge systemUniflo
w scavenge systemPiston rodConnecting rodPiston pinCrossheadThe o
peration between two fuel injections is called a working cycle, w
hich consist of a fixed sequence of events(过程、事件). This cycle may
be achieved either in four strokes(冲程、行程) or two. In a four-stro
ke diesel engine, the cycle requires four separate strokes of the
piston, i.e. suction(吸气), compression(压缩), expansion(膨胀) and exh
aust(排气). If we combine the suction and exhaust operations with
the compression and expansion strokes, the four-stroke engine wil
l be turned into a two-stroke one, as is shown in Figures 1-a)—d)
. Scavenge(a)Compression(b)Injection(c)Exhaust(d)ScavengeportExha
ustportFuel injectorCylinderPistonConnecting rodCrankThe two-stro
ke cycle begins with the piston coming up from the bottom of its
stroke, i.e. bottom dead center (BDC), with the air inlet ports o
r scavenge(扫除、吹除) ports in the sides of the cylinder being opened
(Fig. 1-a)). The exhaust ports are uncovered also. Pressurized f
resh air charges into the cylinder, blowing out any residual(残留的、
剩余的) exhaust gases from the last stroke through the exhaust ports
. As the piston moves about one fifth of the way up, it closes th
e inlet ports and the exhaust ports. The air is then compressed a
s the piston moves up. (Fig. 1-b)). When the piston reaches the
top of its stroke, i.e. the top dead center (TDC), both the press
ure and the temperature of the air rise to very high values. The
fuel injector(喷油器、喷油嘴) injects a fine spray of fuel into the hot
air and combustion takes place, producing much higher pressure in
the gases. The piston is forced downward as the high pressure ga
ses expand (Fig. 1-d)) and the piston continues down until it ope
ns the inlet ports. Then another cycle begins. In the two-stroke
engine, each revolution of the crankshaft makes one power or work
ing stroke, while in the four-stroke engine, it takes two revolut
ions to make one power stroke. That is why a two-stroke cycle en
gine will theoretically develop twice (two times) the power of a
four-stroke engine of the same size. Inefficient scavenging and o
ther losses, however, reduce the power advantage to about 1.8. 1.
More than 50 / above 50 / over 50 50多2. Less than 50 / under
50 / below 50 不到50 或50 以下 The temperature is below 20℃.3. 5
0 more 再加50 ten more days 再10天 Please add 50 more grams of
salt to the water.Jimei university4. a kilometer or more
一公里或一公里多些 a long kilometer 一公里多 a long hour 足足一小时
a dozen 一打，dozens 几十、几打5. 数字+ odd twenty odd / twenty-odd /
twenty and odd / 20多Jimei university6. from twenty to thirty /
twenty to thirty / 从20 到307. some thirty feet / about thirty f
eet / thirty feet or so / 30英尺左右 a hundred more or less / 100上
下 more or less twenty pages / 20页左右8. n time(s) / 增加到n倍，n倍于 The
output has increased (by) threetimes as compared with that of la
st year.Jimei universityWater conducts heat about 20 times better
than air does. 8. 增加多少量， 常用by引出。The coke used has been increased
by 18% as compared with last year.This pipe is 2 inches longer t
han that one.Jimei university9. 降低多少倍：减少n times，译为降低到几分之几，或降低了几分之
几。The new motor is ten times as light asthe old one.新马达的重量是旧马达的十分
之一.The switching time of the new-type transistor is reduced 3 tim
es.新晶体管的开关时间减缩了三分之二.Jimei university10. 减少多少量，常以by引出，为绝对数量。The pr
ime cost decreased by 40%.主要成本下降了百分之四十。This pipe is shorter than
that one by 3 meters.这根管子比那根短3米。Jimei universityEach type of engi
ne has its application(应用) on board ship. The slow speed (i.e. 90
to 120 rev/min) main propulsion(推进装置) diesel operates on the two
-stroke cycle. At this low speed the engine requires no reduction
gearbox between it and propeller. The four-stroke engine (usuall
y rotating at medium speed, between 250 to 750 rev/min) is used f
or alternators and sometimes for main propulsion with a gearbox t
o provide a propeller speed of between 90 to 120 rev/min. Reading
Material Working cyclesA diesel engine may be designed to work o
n the two-stroke or on the four-stroke cycle: both of these are e
xplained below.1、主语如果是用连词and, both…and连接的并列主语，谓语要用复数形式。但是，如果两个词是指
同一个人或同一概念时，谓语要用单数形式。如课文：Both of these (two-stroke and four-stroke
cycle) are explained; Both the m/v “Zheng Zhou” a
nd the m/v “Chang Feng” are 25 000tOcean-going cargo ships design
ed and built entirely by China;Jimei university T
he iron and steel industry is a basic industries.
钢铁工业是基础工业。 The steward and commissar has/have come
. 服务员兼政委 / 服务员和政委已经来了。Jimei university2、主语如果是用成语连词
as well as 连接的两个名词或代词，谓语要与第一个名词或代词的人称和数一致。如： The young mo
torman as well as the others has learned to operate the oil separ
ators. 这位年青机匠，和其他人一样，已经学会操作分油机。Jimei university3、主
语如果是由一个名词或代词和介词 with 与名词、代词组成的介词短语所组成，谓语要与被介词短语所修饰的名词、代词的人称和数一致。例
如： The main engine together with other driven machinery is
running smoothly.主机和其它被带动的机械（一起）正在平稳地运转。 Jimei un
iversity4、主语如果是用连词 or , either…or, neither…nor, not only…but also
连接的两个名词或代词，谓语要与后一个名词或代词的人称和数一致。例如：Neither aluminum nor copper is
easy to corrode.Not only the main engine but also the auxiliary
machines have to be checked at intervals. Jimei university5、主语如果是
集体名词或当作一个整体看待的表示时间、距离、重量的名词复数形式，谓语要用单数形式。例如：30 kilograms is the m
aximum weight for each passenger.每一位旅客携带物品的重量不得超过30千克。Jimei unive
rsity6、主语如果是成对使用的名词，谓语要用单数形式。例如：Trial and error is also a source
of ourknowledge.试验和失败也是（我们获得）知识的源泉。Jimei universityThe four-strok
e cycleFigure 2 shows diagrammatically the sequence of events thr
oughout the typical(典型的) four-stroke cycle of two revolutions. It
is usual to draw such diagrams starting at TDC (firing), but the
explanation will start at TDC (scavenge ). Top dead center is so
metimes referred to as (被称为…) inner dead center (IDC).Proceeding
clockwise (counterclockwise) round the diagram, both inlet (or su
ction) and exhaust valves are initially open. (All modern four-st
roke engines have poppet(提升阀) valves.)If the engine is naturally
aspirated(自然吸气), or is a small high-speed type with a centrifugal
turbocharger(离心式涡轮增压器), the period of valve overlap, i.e. when b
oth valves are open, will be short, and the exhaust valve will cl
ose some(about) 10°after top dead center (ATDC). TDC（firing)Fuel
valve closed(full load)Injection commences≈10-20°BTDCExhaust valv
e opens≈120-150°ATDCExhaust valve closes ≈50-60°ATDCInlet valve o
pen≈70-80 °BTDCInlet valve close≈146-155°BTDCFig 2四冲程定时图Propulsio
n engines and the vast(大量的、巨大的) majority of auxiliary generator e
ngines running at speeds below 1000 rev/min will almost certainly
be turbocharged andwill be designed to allow a generous(充分的) thr
oughflow of scavenge air(横流扫气)at this point in order to control t
he turbine blade temperature.In this case the exhaust valve will
remain open until exhaust valve closure (EVC) at 50-60°ATDC. As t
he piston descends(下降) to outer or bottom dead center (BDC) on th
e suction stroke, it will inhale(吸入) a fresh charge of air. To ma
ximize this, balancing the reduced opening as the valve seats aga
inst the slight ram(进气阀座) or inertia effect of the incoming charg
e, the inlet (suction) valve will normally be held open until abo
ut 25- 35° ABDC (145-155°BTDC). This event is called inlet valve
closure (IVC). The charge is then compressed by the rising piston
until it has attained a temperature of some(about) 550℃. At abo
ut 10-20°(firing), depending on the type and speed of the engine,
the injector admits finely atomized(雾化的) fuel which ignites with
in 2-7°(depending on type again) andthe fuel burns over a period
of 30-50°while the piston begins to descend on the expansion stro
ke, the piston movement usually helping to induce(引起) air movemen
t to assist combustion.At about 120-150°ATDC the exhaust valve op
ens (EVO), the timing(定时) being chosen to promote a very rapid b
low-down(排出、下降) of the cylinder gases to exhaust. This is done: (
a) to preserve(保留) as much energy as is practicable to drive the
turbocharger, and (b) to reduce the cylinder pressure to a minimu
m by BDC to reduce pumping work on the “exhaust” stroke.The risin
g piston expels(排出、驱逐) the remaining exhaust gas and at about 70-
80° BTDC the inlet valve opens (IVO) so that the inertia of t
he outflowing gas, plus the positive pressure difference(正压差), wh
ich usually exists across the cylinder by now (这时), produces a th
rough flow of air to the exhaust to ‘scavenge’ the cylinder.If th
e engine is naturally aspirated the IVO is about 10°BTDC. The cyc
le now repeats. The two-stroke cycleFigure 3 shows the sequence o
f events in a typical two-stroke cycle, which, as the name implie
s, is accomplished in one complete revolution of the crank(曲柄). E
xhaust closes≈110-150°BTDCExhaust opens≈110-120°ATDCInlet opens≈1
30-150°ATDCInlet closes≈130-150°BTDCTDCFuel valve closes (full lo
ad )Injection commences≈10-20°BTDCFig.3二冲程定时图The two-stroke cycle
Two-stroke engines invariably(不变的、总是) have ports to admit air whe
n uncovered by the descending piston.The exhaust may be via ports
adjacent to(邻近) the air ports and controlled by same piston (loo
p scavenge回流扫气) or via poppet exhaust valves at the other end of
the cylinder (uniflow scavenge直流扫气). Starting at TDC combustion i
s already under way and the exhaust opens (EO) at 110-120°ATDC to
promote a rapid blow-down before the inlet opens (IO) about 20-30°later (130-150°ATDC). In this way the inertia of the exhaust gases—moving at about the speed of sound—is contrived(设计、设法) to encourage(促使) the incoming air to flow quickly through the cylinder with a minimum of mixing, because any unexpelled (未排出的）exhaust gases detracts(降低) from the weight of air entrained for the next stroke. The exhaust should close before the inlet on the compression stroke to maximize the charge, but the geometry of the engine may prevent(阻碍) this if the two events are piston controlled. It can be done in an engine with exhaust valves. Injection commences (开始）at about 10-20°BTDC depending on speed, and combustion lasts 30-50°as with the four-stroke. |
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