Ernest Victor Lallier.

An elementary manual of the steam engine; containing also a chapter on the theory, construction and operation of internal combustion engines for the operating engineer online

. (page 13 of 17)
Online LibraryErnest Victor LallierAn elementary manual of the steam engine; containing also a chapter on the theory, construction and operation of internal combustion engines for the operating engineer → online text (page 13 of 17)
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compressed to such a degree that the resulting tem-
perature reaches a point amply sufficient to bum any
Uquid fuel injected into it.

Second, — There is not, properly speaking, an ex-
plosion, such as takes place in the ordinary internal-
combustion engine; but the fuel is burned as it is
introduced into the compressed air, and does not in-
crease in temperature due to compression.

As previously noticed internal-combustion engines
require to be cooled in some manner in order to obtain
efficient operation. This is done either by radiation
directiy through metallic portions of the cylinder to the
air, or by means of water. In a water-cooled engine,
the cylinder and compression spaces, containing also the
valves, are surrounded by a space called the water
jacket, through which a constant flow of water is main-
tained, either mechanically or by means of a pump, or
naturally by thermo-siphon principle. An important
part of the cooling system is the radiator, composed
preferably of copper tubes, provided with large flanges,
in order to present as great a surface to the surrounding
air as possible. The hot water being compelled to flow
through this radiator gives up its heat to the copper
pipes, which, in turn, transfer it to the atmosphere.

In the air-cooled type, which is not suited to stationary
work, the cylinder casting is provided with a number of
wide ribs, or else there are added to it a number of



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INTERNAL COMBUSTION ENGINES. 235

ribs or pins of copper, firmly imbedded in the cylinder
castings, for the purpose of radiating the heat. In this
type, as well as occasionally in the water-cooled type,
cooUng is assisted by a blast of air forced against and
around the cylinder and radiators by means of a large
fan belted to the shaft of the engine.

The ignition of the fuel at the proper moment may be
obtained in several ways: by heated gases and plates,
as in the oil engines; by an open flame or heated tubes,
as in many stationary engines; or by an electric spark,
as is usually the case in engines employed to operate
moving vehicles and in many stationary engines. The
spark may occur in two ways: In the make- and break-
type where the spark is produced on the opening of a
closed electric circuit, or by the jump-spark method in
which a high tension current leaps the space between
two stationary points placed in the compression space.
In either case the result is to ignite the gases. The
current for the spark may be supplied from batteries,
magnetos, or dynamos, operating on either low-tension
or high-tension systems. The former is ordinarily em-
ployed in the make- and break-system. In this case, the
primary current passing through a spark coil, in order
to intensify it, ends in two points projecting into the
compression space and in contact with each other. One
point being movable, its amount, rapidity and time of
movement is controlled by a cam placed on a rod outside
of the cylinder, and in the control of the engine operator.
In the case of the jump spark, a low-tension current
produced by batteries, low-tension magneto or dynamo,
is passed through the primary of an induction coil, pro-



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236 ELEMENTARY STEAM ENGINEERING.

ducing a high-tension current in the secondary of the
spark coil. This high-tension current, or a high-tension
current from a suitable magneto, may be employed. In
either case it is led to two terminals in the form of a

plug (Fig. 94). One side of
the circuit being led to the
terminal a, the other being
grounded at some portion of
the engine frame, forms, by
means of the outer case of
the plug itself, a terminal b;
across the space between these
two, the high-tension current
leaps, producing the spark.
The two terminals are insu-
lated by a non-conductor c,
formed of glass, mica or highly
glazed porcelain. In engines
of one cylinder the contact
which closes the primary cir-
cuit may be closed by a simple
cam and spring. In engines
having two or more cylin-
ders, an apparatus called the
'^•^* "timer" is employed, the

principle of which is illustrated in Fig. 95. One side
of the circuit leading from the hatteries is grounded to
the portion a, and sweeps around, making contact with
the points b and b\ thus closing the circuit through the
induction coils on these particular cylinders, and produc-
ing the spark.



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INTERNAL COMBUSTION ENGINES.



237



The time of spark production may be varied at will
by the engine operator who controls the positions of the
plate carrying the two or more contact points b and &',
closing the individual circuit. Should the spark be
retarded, that is, take place after the piston has ad-
vanced some distance along the stroke, the gases would
already have expanded to a considerable extent, less
initial pressure would result and the engine would
run more slowly. To speed up the engine, the spark
is advanced, that is,
brought to a point
where it will occur at
the instant the piston
passes the dead cen-
ter and begins to re-
turn on the previous
stroke, thereby tak-
ing the fullest advan-
tage of the compres-
sion of the gases.

Fig. 05.

The amount and

quality of the mixture supplied will determine the power
delivered by the engine. Too great a quantity of the
fuel will cause a deposit of carbon to coat the cylinder
at the compression space and the plug. This may ac-
cumulate in the form of small projections which will be-
come highly heated and ignite the gas before the desired
point is reached, or may cause the engine to continue
running after the igniting current has been shut off. It
may also short circuit the plugs, thus providing an easier
path for the current and aconsequent missing of the spark.




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238 ELEMENTARY STEAM ENGINEERING.

On account of their higher pressure, the passage of
the exhaust gases to the atmosphere produces an objec-
tionable noise. This may be overcome by allowing them
first to enter the chamber called the muffler in which
they may gradually expand until a pressure more nearly
that of the atmosphere is reached. They may then pass
to the air in comparative silence.

Gas engine valves are made either with flat or an-
gular spaces, fitting a similar seat, both seat and disc
being ground together in order that there may be no
possibility of leakage when the valve is closed. The
seat is sometimes a portion of the cylinder casting, and
sometimes a separate piece of metal which may be
bodily removed with its valve from the engine in order
to facilitate regrinding. This retaining casting is called
a valve cage. Valves are brought to their seats by
means of springs which hold them firmly in position and
enable them to close quickly.

Stress has previously been laid upon the importance
of having a correct mixture. A little thought will show
that where the wear occurs, due to the valve stem
passing through the cylinder casting, a leakage of air
will also occur, sooner or later, which will interfere
with the quality of the mixture. This has recently
been overcome by the addition of a little attachment
in the form of a collar placed on the valve stem and
retained in position by a slight auxiliary spring. The
opening through which the stem passes is beveled to
fit a similar bevel on the attachment which may be
so arranged as to close in on the stem and compensate
lor wear. As a result, this point is kept tight and an



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INTERNAL COMBUSTION ENGINES. 239

improvement in regulation and efficiency of the engine
is obtained.

As previously mentioned, some valves may be opened
by the atmospheric pressure overcoming the lower
pressure which is produced by the partial vacuum in the
engine cylinder. Others mechanically open and close
by cams placed on a shaft, or sometimes a separate shaft
is provided for the inlet and exhaust valves. This shaft
is geared to the crank shaft in the ratio of 2 to i. It
will also be observed in the description of the two-
cycle engine that there are no valves in an engine of
this type. In consequence of which it is much simpler,
and does not require many of the adjustments of the
four-cycle engine. In setting the valve cams, excellent
results may be obtained by adjusting them so that the
inlet valve begins to open when the crank or, as it is
sometimes called, the throw of the crank shaft has
traveled about lo'' on the suction stroke.

The first five or six degrees of movement of the
crank being almost at right angles to the line of action
of the piston, it will produce no appreciable movement
of the piston. By opening the valve, therefore, a short
distance after center, a slight vacuum will be formed,
and the supply of fuel will start to enter the cylinder
with greater speed, which is a decided advantage. The
exhaust valve may open fifteen or twenty degrees before
the end of the power stroke and close at the center or
five degrees after the end of the exhaust stroke. This
will facilitate the emptsring of the cylinder of almost the
entire amount of burnt gases. These engines are made
with varjdng numbers of cylinders, both to gain power



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240



ELEMENTARY STEAM ENGINEERING.



and to prevent vibration and strain upon the crank
shaft. In Fig. 96 are several diagrams illustrating this
point; those on the left may be called theoretical work
diagrams and are divided into four vertical columns,
representing the four strokes of the cycle. Horizontally
each diagram consists of two colunms, the shaded areas




^QZ^ i



m














~ '^




^'■' iii m



^'"ffiW d




Fig. 96.

of the upper representing work done on the piston in
propelling it forward and doing external work. The
shaded part of the lower colunm is work done during
compression and might be called negative work.

If the fuel is ignited with the engine at rest, the force
of ezpaiision will produce considerable strain on the
shaft, while if the shaft is moving at a sufficiently high
speed the shock will not be of an appreciable amoimt.

The shock or impulse diagrams on the right illustrate



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INTERNAL COMBUSTION ENGINES. 241

this when ignition takes place during one or more strokes,
as shown on the left.

No. I is for a single-cylinder engine, ignition taking
place on the first stroke during which maximum speed
is produced. During the next two strokes nothing is
being produced, and during the last portion the engine
is slowing down and a small amoimt of work is being
done.

Then comes the force and shock of the next ignition,
striking the piston and crank shaft, which are almost at
rest, a hammer blow, which produces a strain of great
amount on the shaft.

The diagram to the right (Fig. 96) would serve to
indicate what we might call the shock or impulse diagram
in this case. If two cylinders are employed, they may
be placed side by side as in the twin engine a (Fig. 97),
or opposite each other as in the opposed engine &.

In the first case, when the power stroke of one cylinder
occurs, momentum is imparted to the fly-wheel, as will
be seen by reference to diagram 2 (Fig. 96) ; when that
stroke is completed and the engine is still in rapid
motion, the second ignition occurs, delivering its power
not with such a sudden shock, but adding simply to the
impetus already acquired by the heavy moving parts.
This advantage, to some extent, lasts during the next
two strokes, where conditions somewhat similar to that
of the single-cylinder engine occur, as are shown by the
diagrams, but not to such an extent as in the first case,
because there is not quite so much opportunity to slow
down as where only one cylinder is employed.

With such an engine, if the course of the cycle be



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242



ELEMENTARY STEAM ENGINEERING.



carefully followed out, it will be seen that it is impossible
to separate the moments of ignition by a stroke during
which no ignition occurs, see a (Fig. 97).

In the two-cylinder opposed engine, as illustrated at
h (Fig. 97), this may be done, and when ignition occurs




Fig. 97.

on the first or power stroke of cylinder o, the piston in
cylinder e is on the suction stroke. On the second
stroke of cylinder o, when it is exhausting, cylinder e
is compressing. On the third stroke, cylinder o is
drawing in the gas, cylinder e is on its power stroke, and
on the last stroke cylinder o is compressing and cylinder
e is exhausting. Therefore, as will be seen from the



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INTERNAL COMBUSTION ENGINES.



243



impulse diagram (No. 3, Fig. 96) on the right, the power
strokes occur alternately, or one during each revolution.
In the meantime the engine has not had an opportunity
to slow down to any appreciable extent. In consequence
of which, the shocks are less wearing on the machine,
and the vibration is far less than in the previous cases.

1 a 3




Fig. 98.

If, now, the engine be equipped with four cylinders
(Fig. 98), we will have an engine similar in results to
two opposed engines and on each stroke we will have a
power impulse and compression; therefore, the impulse
diagram will read as shown in (No. 4, Fig. 96), or prac-
tically a continuous turning movement is the result.
The firing order of the cylinders in such an engine, read-
ing from the left, might be arranged in the following
order: Cylinders i, 2, 4, and 3.

Engines are sometimes constructed with three cylin-
ders, enabling the cranks to be placed at an angle of



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244 ELEMENTARY STEAM ENGINEERING.

120'' to each other, with the idea of relieving the strain
on the crank shaft. This is an excellent method for
obtaining the desired results, but probably not as satis-
factory as where four cylinders are employed.

In order to determine to some extent the horse power
developed by a four-cycle gasoline engine the following
formula may be employed:

0.7S54X€fiXPXeXLXXXn j^^
2 X 12 X 33>ooo

n = the number of cylinders.
X = the revolutions per minute.
X = the stroke in inches.
r = the M.E.P. during the power stroke.
e = the efficiency factor.

The values of I* and e, are not always readily deter-
mined with the means ordinarily at hand but may in a
good engine be assumed to be respectively 70 pounds
for 1*, and 0.75 for e.

We have, therefore, practically the same formula as
that used in calculating the horse power of a steam
engine.

This formula applies when the engine is nmning at its
best speed for developing power; that is, about 800 revo-
lutions for a motor of six-inch stroke, or 1200 revolutions
for one of four-inch stroke.

However, owing to the many different and varying
conditions developed in gas-engine operation no thor-
oughly satisfactory rule meeting all conditions has yet
been developed. The Association of Automobile Manu-



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INTERNAL COMBUSTION ENGINES. 245

facturers has adopted the following formula based on
a piston speed of 1000 feet per minute.

-_ _. <f* X No. cylinders

ll.ir. = 1 •

Several diagrams illustrating methods of wiring for
jump-spark ignition purposes are shown in Fig. 99.
The simplest form is that used with a single-cylinder
engine employing a battery as the source of current
supply, and an induction coil to produce the high-
tension current. This method is shown in Diagram
No. I. When the switch is closed, current from the
battery will flow through the primary circuit ^9 through
the coil C to the ground connection G^ thence along the
engine frame as indicated by the dotted lines to the
timer shaft Of whenever the circuit is completed by
the roller :r touching the contact block B.

The induced current flows through the secondary
circuit 89 through the plug, and completes its circuit
through the ground and a part of the primary circuit,
as indicated on the diagram.

A diagram for a four-cylinder engine with four coils
is shown by No. 2. The timer has four contact-blocks,
Nos. I, 2, 3, 4, each being connected to a coil, each
coil being in turn connected to a spark plug in one of
the cylinders. The timer is so connected that ignition
will be produced in the cylinders in proper order as
previously explained.

In such cases two sets of batteries are usually car-
ried, and either one may be used by means of the
switch shown.



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246 ELEMENTARY STEAM ENGINEERING.



r — n



A



Wr



I i{\i i |j> iifid



UU^



-9



I — J

I




ML



v\ W'l ^^ m





Fig. 99.



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INTERNAL COMBUSTION ENGINES. 247

Where a magneto is used to produce the spark an
auxiliary battery is frequently employed to facilitate
starting the engine. Diagram No. 3 shows a method
of wiring for this purpose.

With the switch on the battery side the primary
current energizes the coil and passes through the in-
terrupter of the magneto, to which it is connected at I.
The distributor of the magneto I> serves to deliver the
secondary current to the proper plug. When the engine
is running the switch is thrown to the magneto side
and the battery is cut out.

QUESTIONS.

1. What is the principle of operation of an internal-combustion
engine?

2. Describe the four-part cycle.

3. Describe the two-part cycle.

4. Wherein does this type of engine differ from a steam en-
gine?

5. What is a carburetter? Describe it

6. What is the cooling system?

7. Why are multi-cylinder engines preferable?

8. How are the valves operated?

9. What is a gas producer?
10. Describe its operation.



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CHAPTER XX.
LUBRICATION.

When a piece of material is caused to slide over an-
otheri a certain amount of work is required to overcome
the friction between the pieces. If these are moved
with considerable speed heat will be produced. Should
one of them be practically encircled by the other, as is
the case of a shaft rotating in its bearings, the heat may
cause sufficient expansion of the inner portion to make
them bind closely together, thus requiring more work
to move them, or perhaps requiring so much power to
move them that it is entirely beyond the ability of the
machine to do so, and it stops.

The normal friction, that is, friction due to ordinary
causes, will be increased, depending on the diameter of
the revolving shaft, on the weight placed upon it and
upon the speed at which it revolves. The smoother the
surfaces, the less friction there will be. Also, there
will be more friction if both parts are of the same ma-
terial. This is probably due to the fact that two pieces
of material of the same kind and of the same quality will
have molecules of the same size and of the same general
form, $0 that when one piece moves over the other the
projections on one piece drop readily into the depres-
sion in the other, somewhat after the manner in which
the teeth of a gear wheel lock together. When dis-
similar metals are employed for the shaft and bearings,

248



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LUBRICATION. 249

or for the stationary and movable parts of a piece of
machinery, the particles composing them being of dif-
ferent size, those of one piece cannot drop so deeply into
the depression on the other, and consequently less fric-
tion is produced.

In an engine, like all other pieces of machinery, we
have many places where friction occurs, due to the
moving of one surface on the other. We have parts of
varying diameter, such as a crank shaft, or crank pin.
We have the pressure exerted on these parts, too ; for ex-
ample, the pressure on the piston, the weight of the fly-
wheel, the pull of the belt, the pressure on the guides
and several other parts. In addition to the above we
have, particularly in the cylinder, moving parts some-
what difficult to reach with the oil and exposed to a con-
siderable degree of heat from the steam. On these
places where friction occurs, materials of different quality
are employed to reduce the friction for the reason pre-
viously given.

In the case of the connecting rod and crank pin, the
end of the rod is fitted with bronze or gun metal bear-
ings. This material is an alloy, varying in composition
with regard to the service for which it is to be employed.
A good grade is composed of about 90 parts of copper
to 10 parts of tin. The hardness may be increased by
increasing the proportions to 14 parts of tin to 86 parts
of copper. In other bearings the bearing proper is
recessed, and this recess is filled with some metal
which has especially good anti-friction qualities, such,
for example, as babbitt. This is a soft, white-colored
aUoy of copper, tin and antimony, in the proportion of 4



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250 ELEMENTARY STEAM ENGINEERING.

parts of copper, 24 parts of tin, and 8 parts of antimony.
This is made into an alloy first, and then remelted with
twice its weight of tin. When used it is melted and
poured into the bearing with the shaft in place. It
makes a smooth highly polished surface in which the
friction is reduced to a remarkable extent. The me-
chanical reduction of friction is further obtained by
making bearings partly of babbitt or bronze, containing
grooves or recesses filled with graphite, or black lead.
This, in its commercial form, is a shiny black, smooth,
greasy feeling material, which is in itself an excellent
lubricant.

Various constructions of modem machinery provide
for bearings composed of balls or rollers formed of hard
steel which support the shaft and, rolling around with
it, also revolve upon their own centers, thus eliminating
to a very great extent all sliding motion as in a plain
bearing, and producing a rolling motion only. These
methods of reducing friction, however, are not alto-
gether satisfactory when taken alone. Recourse must
be had to additional lubrication in the form of oils or
grease which should be carefully selected with regard
to the work to be performed.

A theoretically perfect lubricant is one which will
penetrate to all portions of the bearing, form a thin film
between the moving parts and remain there, entirely
separating them, so that the moving parts of a properly
lubricated bearing should never actually touch each
other. Under these conditions the ideal bearing is that
of a shaft rolling upon a large number of small spherical
bodies represented by the drops or molecules compos-



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LUBRICATION. 251

ing the lubricant. Such lubricants in the form of liquids
and semi-solid materials are called oil and grease.
They vary in density according to the work to be per-
formed.

A thin oil will not serve for a heavily weighted, slowly
moving bearing, as it would be pressed out without doing
any service, while a hard grease would not serve for a
light and rapidly moving bearing, on account of not
being sufficiently fluid to flow properly where desired.
For many purposes, animal or mineral oils are used,
but the animal oils are exposed to the objection that
when decomposed they are liable to liberate acids or
other substances which are injurious. In the case of
engine cylinders, where, on account of the intense heat,
the oil is likely to be evaporated or decomposed quickly,
mineral oils are used.

Briefly stated, mineral oil is that which is drawn from
the earth, being the product of natural causes during
many ages of the earth's existence. It is supposed that
at some period, long ago, vast quantities of animal and
vegetable matter were caught during some convulsion
of the earth and held between masses of material which
afterwards solidified in the form of rock. Heat and
pressure, due to the contraction of the earth, gradually
squeezed out all the oil which collected in pockets in
certain portions of the earth where oil is found. This
same cause also distilled from the oils and materials
which produced them certain lighter products or gas.

Occasionally these gases are found in spaces in the
earth's surface connecting with the spaces in which the
oil is fotmd. If in drilling in an oil region, a body of oil



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252 ELEMENTARY STEAM ENGINEERING.

is Struck which is connected by natural passage ways
with a body of gas, on removing the drill and releasing
the pressure, the gas forces the oil ahead of it out of
the well pipe. This is called a '* gusher." If there is
no gas present or its pressure has been reduced then
the oil must be pumped out of the well. Oil in this form
is called crtide oil. It has a specific gravity varying
from 0.77 to 0.98. All crude oils have a fluorescence,
var]ring from dark green to blue, and a very noticeable
odor. The process of distillation is now undertaken,


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Online LibraryErnest Victor LallierAn elementary manual of the steam engine; containing also a chapter on the theory, construction and operation of internal combustion engines for the operating engineer → online text (page 13 of 17)