In the sliding sleeve type of four strok_Practical Hand Book of Gas, Oil and Steam Engines Stationary, Marine, Traction; Gas Burners, Oil Burners, Etc.; Farm, Traction, Automobile, Locomotive; A simple, practical and comprehensive book on the construction, operation and repair of all kinds of engines. Dealing with the various parts in detail and the various types of engines and also the use of different kinds of fuel.

lifting type of valve as shown in Fig. 4, is replaced by a peculiar type

of slide valve similar in action to the slide valves used on steam

engines, except that it is cylindrical in form and entirely surrounds

the piston. While there is a change in the form of the valve, and in a

number of small details, the gases are drawn into the cylinder,

compressed, ignited, and released in exactly the same way and in the

same rotation, as in the poppet valve engine just described. A

description of the Knight engine which is the most prominent example of

the slide sleeve motor will be found in a succeeding chapter. Since the

success of the slide valve type has been acknowledged by many prominent

automobile manufacturers, there have been several similar types placed

on the market, some with two sleeves and some with one, but in all cases

the designers have had but two points in view, that is quiet running and

free passages.

(26) Two Stroke Cycle Engine.

Two stroke cycle engines perform the five events of aspiration

(suction), compression, ignition, expansion and release in two strokes

or one revolution. Providing that these events are performed as

efficiently as in the four stroke cycle engine, it is evident that with

equal cylinder capacity, the two stroke cycle engine would have twice

the output of a four stroke cycle since it gives twice the number of

impulses per revolution. Unfortunately it is impossible to attain twice

the output of the four stroke cycle type with the small two stroke

engines built at the present time because of their imperfect scavenging

and poor fuel economy. In the larger two stroke engines, the pumps and

blowers used for scavenging the cylinders consume a considerable

percentage of the output.

[Illustration:

Fig. 5. Diagram of Two Port—Two Stroke Cycle Engine, Showing the

Events in the Crank-Case and Cylinder.

]

A general classification of the two stroke cycle engine is not so simple

a matter as that of the four stroke because of the differences in

construction of large and small sizes. This difference between the large

stationary engine and the small type commonly used on boats is due to

the efforts of the builders of the large engine to obtain great fuel

economy, while the chief endeavors of the builders of small engines is

to build a simple and reliable engine for the use of inexperienced

persons. While the smaller type of two stroke engine (less than 25

horse-power) has not been used in stationary practice to any extent,

owing to the defects just named, or on automobiles, it has been widely

used on motor boats, a service for which it is peculiarly adapted. Its

extended use on boats is due to the fact that in such service it runs at

practically a constant speed and works against a steady load, the

conditions that are most favorable to the type. With automobiles where

the motor speed is constantly varying, as well as the load, this type of

motor is not flexible enough to meet the continually varying conditions.

The small two stroke motors are divided into two principal classes, the

two port and three port type, depending on the method by which the

charge is transferred to the cylinder. No valves are used in the

cylinders of either type for the admission or release of the gases. As

the two strokes of the cycle are the compression stroke and working

stroke, it is evident that the charge must be introduced into the

cylinder by means other than by the suction of the piston and at a time

when there is no pressure in the cylinder. This is accomplished by a

preliminary compression of the charge in the crank case which places the

mixture under sufficient pressure to force it into the cylinder at the

end of the working stroke and at the same time to displace the burnt

gases left from the previous explosion. It should be noted that the

incoming mixture is a substitute for both the suction and scavenging

strokes of the four stroke cycle engine.

A diagrammatic view of a two port, two stroke cycle engine is shown by

Fig. 5, in which P is the piston, C the crank case, I the transfer port,

V the inlet valve, E the exhaust, and S the spark plug for igniting the

charge. It should be noted that there are no valves in the cylinder and

only three moving parts. The cycle of events for the two port type is as

follows:

=STROKE 1.= We will consider the piston to be moving up on the

compression stroke as shown in view (A), compressing the mixture in the

combustion chamber D. While moving upwards in the direction of the

arrow, the piston creates a vacuum in the crank case C drawing fresh

mixture into the crank case. The piston at this time is covering the

opening of the transfer port I and the exhaust port E so that the

compressed mixture in the cylinder cannot escape. On reaching the end of

the compression stroke, a spark occurs at S which drives the piston down

and turns the crank towards the right as shown by the arrow.

=STROKE 2.= When the piston uncovers the exhaust port E on its downward

working stroke as shown by view B, the exhaust gases being under

pressure rush out into the atmosphere as shown by the arrows, and

relieve the pressure in the cylinder. Some of the burnt gas remains in

the cylinder at atmospheric pressure as there is no scavenging action up

to this point. While the piston has moved down on the working stroke it

has compressed the mixture in the crank case ready for admission to the

cylinder. The valve V prevents the escape of the gas during the

compression.

On reaching the end of the stroke the piston uncovers the transfer port

which allows the compressed mixture in the crank case to rush into the

cylinder through I, as shown by view C. Owing to the shape of the

deflector plate Z on the piston head, the stream of mixture issuing from

I is thrown up toward the top of the cylinder, as shown by the arrows,

and consequently sweeps the remainder of the burnt gas before it through

the exhaust port E. In this way the fresh mixture from the crank case

scavenges the cylinder and fills it in one operation. Being filled with

gas, the piston now moves up on the compression stroke for the next

explosion as shown by view A.

Unfortunately the scavenging action of the incoming gas is not complete

for the whirling motion of the charge causes it to mix with the residual

gas to a certain extent which, of course, reduces the heating effect of

the fuel and reduces the power output. Another factor that reduces the

output of this type of engine is the loss of explosive mixture through

the exhaust port at low engine speeds with an open throttle. In this

case, the piston speed being low, part of the mixture has time to pass

over the deflector plate and through the exhaust opening before the

piston closes the exhaust port. At very high speeds the charge is

diluted by a considerable quantity of burnt gas which has not had time

to escape through the port causing a further loss of power. With the

throttle nearly closed on a light load, the impact of the incoming

mixture is so slight that the percentage of exhaust gas left in the

cylinder is very high. This dilution is so great that with moderately

low speeds (easily within the capacity of the four stroke cycle engine)

it is either impossible to ignite the charge or it is impossible to

ignite two in succession.

In marine service where the loads are constant, and the speeds fairly

uniform, there is but little trouble from the last mentioned source, and

as the fuel is usually a smaller item than the repair bill, the

simplicity of the small two stroke engine with its freedom from

mechanical troubles usually gives satisfactory results in the hands of

the novice.

(27) Three Port—Two Stroke Cycle Engine.

The principal difference between the three port and two port types of

the two stroke cycle engine is in the manner in which the charge is

admitted to the crank case for the initial compression. In the two port

motor, as previously described, the check valve “V” opens to admit the

charge, and closes during its compression in order to prevent its escape

through the opening by which it was admitted to the cylinder. With the

three port type there is no check valve in the crank case, the admission

and the retention of the charge being controlled by the movement of the

piston in practically the same way that the piston controls the opening

and closing of the exhaust and transfer ports in the cylinder.

[Illustration:

Fig. 6.

]

[Illustration:

Fig. 7

]

Figs. 6–7. Diagram of Three Port—Two Stroke Cycle Engine in Two

Positions.

By the piston control of the gases in the crank case, the valve is

eliminated, which makes one less moving part to cause trouble and

expense, and permits the use of the same type of carburetor that is used

on the four stroke cycle engine. As the check valve opens and closes at

a high speed, (twice that of the valves on a four stroke cycle engine),

there is considerable wear on the valve seats due to the continuous

banging, which results finally in a loss of the initial compression.

When the initial compression is reduced in this way the engine loses

power because of the reduction of the charge in the cylinder.

While the three port type is free from valve leakage troubles, it has a

steady loss due to the high vacuum that exists in the crank chamber when

the piston is on its upward stroke. This vacuum drags against the piston

and absorbs a considerable amount of power until the piston reaches the

upper end of the stroke. At this point the inlet port is opened and the

vacuum is broken by the rush of the mixture through the inlet port.

Besides the power loss, the vacuum has a bad effect on the lubrication

of the main crank shaft bearing.

[Illustration:

Elevation of Fairbanks-Morse Three-Port Two Stroke Marine Motor

Showing Warming Device for Carburetor Air.

]

Described by strokes, the cycle of events in the three port, two stroke

cycle engine is as follows:

=STROKE 1.= In Fig. 6, the piston is shown at the end of the compression

stroke with ignition taking place in the combustion chamber C. The

pressure due to the expansion drives the piston down on the working

stroke at the same time causing the initial compression of the mixture

in the crank case as shown by Fig. 7. The gas in the crank case cannot

escape during compression as the inlet port A is covered by the piston.

(a) As the piston descends, its upper edge uncovers the exhaust port D,

allowing the greater portion of the exhaust gases to escape and reduces

the pressure in the cylinder to that of the atmosphere.

(b) Descending a little farther, the top of the piston uncovers the

opening of the transfer port B, allowing the compressed gases in the

crank case to enter the cylinder as shown by the arrows. These gases,

guided by the deflector plate on the top of the piston are thrown

upwardly, as shown by the arrows, and sweep the residual burnt gases

before them through the exhaust port. The cylinder is now filled with

the combustible mixture ready for compression.

=STROKE 2.= The piston now moves up on the compression stroke,

compressing the charge in the cylinder and at the same time creates a

vacuum in the crank-case. Just before the piston reaches the end of the

exhaust stroke, the lower edge of the piston uncovers the inlet port A

(See Fig. 7), which allows the mixture from the carburetor to flow into

the partial vacuum and fill the crank case ready for the next initial

compression. When the end of the stroke is reached, the charge in the

combustion chamber C is fired and the cycle is repeated. It should be

noted that the incoming gas and the initial compression are controlled

entirely by the action of the lower edge of the piston on the inlet port

(28) Reversing Two Cycle Motors.

As the admission and exhaust in the two stroke cycle engine each occur

once per revolution, and are controlled directly by the piston position

at opposite ends of the stroke, it is evident that the direction of

rotation is not affected by gas control or valve timing, as in the case

of the four stroke cycle engine. The factor that does determine the

direction of rotation in the two stroke engine is the time at which

ignition occurs in regard to the angular position of the crank. By

changing the relation between the crank position at the end of the

compression stroke and the time at which the spark occurs, it is

possible to reverse the engine even when it is running.

Should the engine be standing still in the position shown by Fig. 6,

with the crank on the dead center, when ignition occurred, there would

be no more tendency to turn the crank to the right than to the left,

providing of course, that there was no effect from the momentum of a

revolving fly wheel. If ignition occurred with the crank inclined ever

so little toward the right, the pressure of the piston would force the

crank downwards in a right handed direction. If the crank were inclined

to the left, the tendency would be for left handed rotation.

If the ignition system were arranged so that the spark occurred when the

crank was inclined towards the right every time that the piston came up

on the compression stroke, we should have continuous rotation in a right

hand direction. By shifting the sequence of the spark so that it

occurred with the crank on the left we would cause the engine to stop

and reverse to left handed rotation. This is exactly the method used in

reversing two stroke motors in practice, the change in the ignition

being accomplished by advancing or retarding the mechanism that

dispatches the spark (“Timer” or “Commutator”).

[Illustration:

Fig. F-9. Cross Section of Fairbanks-Morse Three Port—Two Stroke Cycle

Engine, with Parts Named.

]

This is an advantage not possessed by the four stroke cycle engine of

the ordinary type, as the cams and valve mechanism require reversal as

well as a reversal of the ignition system. This relation between the

valve action and rotation in a four stroke cycle engine may be

illustrated by the following example. Consider the piston at the end of

the compression stroke in an engine designed for right hand rotation.

After ignition, under the proper conditions, the piston would descend

turning the crank to the right until it reached the bottom of the

stroke, at which point the exhaust valve would open and relieve the

pressure in the cylinder.

Let us now consider an attempt at reversing the engine by causing the

spark to occur before the piston reached the end of the compression

stroke with the crank still inclined toward the left. In this case the

piston would force the crank down in a left hand direction until it

reached the end of the stroke. The exhaust valve would not open to

relieve the pressure, as the exhaust cam would be moving away from the

valve rod instead of toward it. Should the crank swing a little past the

dead center, because of its momentum, the inlet valve would be opened

instead of the exhaust, and the contents of the cylinder would shoot

through the intake pipe and carburetor. This would bring matters to a

close as far as rotation was concerned.

The opening of the inlet valve on the reversed working stroke would

occur as the inlet valve closes one stroke, or one-half revolution,

before the end of the compression stroke. As the engine turned backward

one-half revolution, the inlet cam would again be brought into contact

with the inlet valve rod, opening the valve and allowing the burned

gases to pass through the carburetor. Should the pressure be

sufficiently reduced by inlet valve to allow the piston to reach the end

of the second stroke, it would start on the third stroke by inhaling a

“charge” of burnt gas through the exhaust valve which would now be open.

(29) Scavenging Engines.

As the piston does not sweep out all the cylinder volume because of the

space left at the end of the cylinder for compression, more or less

burned gas remains in the combustion chamber which dilutes the active

mixture taken in on the suction stroke. Not only are the residual gases

useless in generating heat but they also occupy a considerable space in

the cylinder that might otherwise be filled with a heat producing

mixture. Their diluting effect also prevents the complete combustion of

a certain percent of the fuel actually taken into the cylinder for which

the burnt gas is incapable of supporting combustion.

The amount of burnt gas remaining in the cylinder depends upon the cycle

of the engine and also upon the valve timing and size of the exhaust

piping. In the four stroke cycle engine the volume of residual gas is

equal to the volume of the combustion chamber, in the two stroke cycle

it varies from one-tenth to one-third of the entire cylinder volume,

depending on the load and speed. With correct design and free exhaust

passages, the gas held in the clearance space of a four stroke cycle

engine is at a pressure considerably below that of the atmosphere, and

consequently its actual volume is even less than the volume of the

combustion chamber.

Many systems have been devised for the purpose of clearing the cylinder

of burnt gas in order to minimize the loss of fuel in large engines, but

owing to their complication have never been successfully applied to

small engines of the automobile or marine types. In general, the

“scavenging” is accomplished by pumping out the clearance space at the

end of the scavenging stroke, while fresh air is admitted to the

cylinder through the inlet valves, or by blowing out the clearance space

by a blast of pure air furnished from an air pump attached to the

engine.

There have been several systems proposed by which the gas in the

cylinder is withdrawn by the inertia of the exhaust gas in specially

designed ejectors, and by the compression of fresh air in the crank case

of the engine. The former system known as “organ pipe ejection,” is by

far the simplest method of all as the ejector is simply a tube without

moving parts, and it also possesses the additional advantage of reducing

the back pressure on the piston. Unfortunately these advantages are

obtained only at certain loads, and with certain velocities of the

exhaust gases, which makes it impossible to obtain even approximately

correct scavenging at other loads and speeds.

When air pumps are used for scavenging, a great percentage of the

economy obtained is offset by the power required to operate the pumps.

In addition to the frictional losses of the pumps, are the increased

maintenance charges and repair bills.

CHAPTER IV

INDICATOR DIAGRAMS

(35) General Description.

A brief description of the indicator as a means of recording the

pressures in the cylinder of a simple heat engine in relation to the

piston position was given in paragraph (6), Chapter I, and as this

instrument is so peculiarly adapted to locating the events taking place

in the cylinder we will devote some space on its application to the

practical gas engine cycles described in the preceding chapter. Since

each event in the cycle is accompanied by a corresponding increase or

reduction in pressure, the beginning or end of an event will be

indicated on the diagram by a change in the vertical height of the curve

above the atmospheric line, at some particular piston position. The

piston position will be in the same relation to the total stroke as the

pencil position will be to the horizontal length of the card.

If the event, for example, as indicated by a drop in pressure, be at the

center of the card, it will show that the drop in pressure took place

when the piston was in the center of the cylinder or at mid-stroke.

Should the pressure change at a point one-quarter of the card length

from the starting point of the pencil, it shows that the event took

place in the cylinder when the piston had accomplished the first quarter

of its stroke, and so on. It should be noted that horizontal distances

on the indicator card denote piston positions, and the vertical

distances, pressures.

As explained in a former paragraph the length of the vertical lines

represents certain definite pressures, each inch of length representing

so many pounds as per square inch, the exact amount per inch depending

on the indicator spring strength or adjustment. To make this point

clear, all of the indicator diagrams shown in this chapter will be

provided with a scale of pressures at the left of the diagram by which

the pressure at any point may be accurately measured off for practice.

It should be noted that points on the curves which are above the

atmospheric line represent positive pressures above the atmosphere, and

that the points lying below the atmospheric line represent partial

vacuums which may be expressed as being so many pounds per square inch

below the atmosphere. The vacuum pressures indicate the extent of the

“suction” created by the piston when drawing in a charge of air and gas.

Straight vertical lines show that the increase of pressure along that

line has been practically instantaneous in regard to the piston

velocity, for if the pressure increased at a slow rate this line would

be inclined toward the direction in which the piston was moving, as the

piston would have moved a considerable distance horizontally while the

pencil was moving vertically. This inclination of the vertical line

gives an idea of the rate at which the pressure increases in relation to

the piston speed, the greater the inclination, the slower is the rate of

pressure increase. Straight horizontal lines that lie parallel to the

atmospheric line denote a constant pressure or vacuum.

The rate at which horizontal lines descend or incline to the atmospheric

line represents the rate at which the pressure increases or decreases,

in respect to the piston position (not piston velocity). A steep curve

represents a rapid expansion or compression from one piston position to

the next. A waving or rippling line indicates vibration due to valve

chattering or explosion vibrations. A straight inclined line shows that

the pressure is decreasing or increasing in direct proportion to the

piston position.

(36) Diagram of Four Stroke Cycle Engine.

By referring to paragraph 25, Chapter III, it will be seen that the five

events of suction, compression, ignition, expansion and exhaust are

accomplished in four strokes, in the following order:

Stroke 1. Suction—(Mixture drawn into cylinder).

Stroke 2. Compression—(Mixture compressed).

Stroke 3. { Ignition.

{ Expansion (working stroke).

Stroke 4. Exhaust—(Scavenging stroke).

These events with the pressures incident to each drawn to some relative

scale are shown graphically in Fig. 10 by four lines representing the

four strokes of the piston. In order to show the relation between the

diagram and the piston, a sketch of the cylinder with a stroke equal to

the length of the diagram is shown directly beneath the curve. The

vertical line IJ is the scale of pressures (somewhat exaggerated in

order that the small vacuum and scavenging pressures shall be clearly

shown). The line marked “atmosphere” represents atmospheric pressure and

it is from this line that all measurements of pressure are taken.

[Illustration:

Figs. 10–11–12. Showing Respectively a Typical Four Stroke Diagram,

Retarded Combustion and Retarded Spark.

]

Consider the piston starting on the suction stroke, the piston moving

from the position L to K, or from left to right. The movement creates a

partial vacuum in the combustion chamber N which is shown on the diagram

as the distance OA, equal to 2 pounds below atmosphere according to the

pressure scale. The suction line remains at this distance below the

atmospheric line until within a short distance of the end of the stroke

when it rises to meet the atmospheric line at B when the piston reaches

the end of the stroke at K. This rise at the end of the stroke is due to

the fact that the piston moves more slowly when approaching the end of

the stroke while the velocity of the incoming gases remains nearly

constant so that the piston exerts no pull nor suction. On the diagram

the entire suction stroke is represented by AB.

The piston now returns on the compression stroke from K to J compressing

the mixture in the combustion chamber N. On the diagram this stroke is

shown beginning at B, with the pressure slowly rising until the pressure

is a maximum at the point C at the end of the stroke. During the

compression, the pressure has risen from that of the atmosphere at B to

125 pounds pressure at C as shown by the scale. At a point slightly

before C is reached, ignition occurs, and the pressure rapidly rises

from C to D, due to the expansion of the heated gas. In this case the

combustion is practically instantaneous as shown by the straight,

vertical combustion line CD.

At D the piston starts on the working stroke from left to right

increasing the volume of the gas and at the same time diminishing the

pressure because of the expansion until the maximum pressure of 400

pounds per square inch at D is reduced to 30 pounds per square inch at

E, the line DE being called the expansion line. During this time the

heated gas has been performing work on the piston. At E the exhaust

valve opens and the pressure drops from E to T, a point still about 10

pounds above atmospheric pressure. Theoretically the pressure should

drop instantly from E to atmosphere, or from 30 pounds per square inch

to zero, but practically this is impossible because of the back pressure

due the slow escape of the exhaust gases through the comparatively small

valve openings and exhaust pipes. Since considerable pressure is exerted

by the piston on the return stroke in forcing the gases out of the

exhaust valve, the exhaust line TO on the diagram is nearly 10 pounds

above the atmospheric pressure from T to O. At a point near O, the

piston slows up on nearing the end of the stroke so the gases have more

time to escape through the valves, and the pressure drops to the

atmosphere, ready for the succeeding suction stroke.

It should be noted that the points A, B, E, and F represent periods of

valve action. At A the inlet valve opens; at B the inlet closes; at E

the exhaust opens; at F the exhaust closes, and at A the inlet again

opens at the beginning of the suction stroke AB. That this is true is

apparent from the fact the inlet must open at the beginning of the

suction stroke, and both valves must be closed from the point B to the

point E in order to prevent the escape of the compressed charge and

expanded gases from the cylinder. At the end of the working stroke the

exhaust valve must liberate the gases and remain open to the end of the

scavenging stroke to eliminate the residual gas while the closed inlet

valve prevents the burnt gases from being forced through the inlet pipe

and carburetor.

As shown on the diagram, the exhaust valve closes at the same time that

the inlet opens, as F, and O both occur on the same vertical line DL.

This is true theoretically, but owing to the different conditions met in

practice, the actual setting of the valves may vary slightly from that

shown on the diagram. Some makers of high speed engines open the inlet

slightly before the exhaust closes as it is claimed that the inertia of

the exhaust gas passing through the exhaust pipe creates a slight vacuum

that is an aid in filling the cylinder with a fresh charge. It should be

borne in mind that this condition only exists when the piston has come

to rest and exerts no pressure on the exhaust gas. The vacuum is due to

the velocity inertia of the gas after it has been reduced to atmospheric

pressure. Other makers close the exhaust valve a very little before the

inlet opens, but no matter what the setting, the difference in the time

of opening and closing is very small, and the results obtained probably

differ by an almost negligible amount.

During the suction and scavenging strokes, the fly wheel of the engine

is expending energy on the gas since it is moving a considerable volume

at a fairly high pressure. In the case of the scavenging stroke, the

piston is working against 10 pounds back pressure, which on a 10 inch

piston would amount to a force of 785 pounds. With the 2 pound vacuum

the drag on the piston would amount to 157 pounds, no small item when

the velocity of the piston is considered. Of course the pressure of 10

pounds per square inch is rather high, but it is often attained with

long and dirty exhaust pipes. It is items of this nature that cut into

the efficiency of the engine, and increase the fuel bills, and it is

only by the indicator that we can determine the extent of such “leaks”

and remedy them.

Since the area of the indicator card represents the power of the engine,

it is evident that we lose the power represented by the area included in

the rectangle FEBO on the scavenging stroke plus the area BOA on the

suction stroke. The area included in BCO represents the work taken from

the engine in compressing the charge, but this is returned to us during

the next stroke plus the benefits gained by compressing the mixture. The

arrows show the direction in which the piston is moving during that

event.

An actual engine does not follow the form of the diagram shown by Fig.

10 exactly because of certain conditions met with in practice such as

imperfect mixtures, faulty valve and ignition timing, small valve areas

or leakage. The combustion in the real engine is neither instantaneous

nor complete but it approximates the “=IDEAL=” cycle just described more

or less closely with a high compression and a fairly well proportioned

mixture.

(37) Detecting Faults With the Indicator.

For the best results the gas must be completely ignited at the point of

maximum compression, and the pressure must be established on the dead

center, so that the indicator card will show a straight and vertical

combustion line. As all gases require a certain length of time in which

to burn, the ignition should have =LEAD=, that is, should be started

before the end of the stroke so that combustion will be complete at dead

center. The amount of ignition lead required depends on the fuel and the

compression. In Fig. 10 the point of ignition (I) is shown as occurring

before the end of the compression at (C), which insures a straight

combustion line CD.

With a lean or slow burning gas, that is, a gas slower than used on the

diagram, combustion would not be complete at the end of the stroke if

the same point of ignition were used. This effect is shown by Fig. (11),

in which the full line diagram BCDE represents the ideal diagram (Y),

and BCFG represents the slow burning mixture with the same point of

ignition (X). The compression curves of both diagrams are coincident as

far as C, the ideal diagram shooting straight up at this point and the

weak mixture diagram staying at the same level. When under the influence

of the mixture (X) the piston starts from left to right and reaches the

point F before the slow burning gas reaches its maximum pressure. During

this part of the stroke there has been very little pressure on the

piston and it will be noticed that the maximum pressure is far below

that of the ideal diagram. This low maximum is due principally to the

reduced compression under which the gas has been burning, from C to F.

[Illustration:

Figs. 13–14. The First Diagram (13) Shows a Two Port Two Stroke

Diagram, the Second Shows a Typical Diesel Card.

]

As the gas has but a small part of the stroke left in which to expand,

the pressure at the point of release is much higher than the release

pressure of the ideal diagram, which means that a considerable amount of

heat and pressure have been wasted through the exhaust pipe. Besides the

heat loss, the high temperature of the escaping gas has a bad effect on

the exhaust valve and passage. The great volume of gas passing through

the exhaust valve also increases the back pressure on the scavenging

stroke.

Delayed or retarded ignition will cause a low combustion pressure and

slow combustion with any type of fuel or compression pressure as will be

seen from Fig. 12. In this case the compression pressures of the ideal

diagram Y and the diagram X showing the retarded spark are of course the

same, the compression line extending from B to C in the direction of the

arrows. At C the ignition occurs for curve Y, and the pressure

immediately rises to D. In the case of curve X, ignition does not occur

until the point I is reached, the compression falling on the line CI

with the forward movement of the piston as far as the point I. At this

point the compression pressure is very low which results in the slow

combustion indicated by the slant of the combustion line IF. The point

of maximum pressure F is much below D of the ideal curve, and as there

is no opportunity for complete expansion during the rest of the stroke,

the release pressure is high causing a great heat loss. If running on a

=LATE= or =RETARDED= spark is continued for any length of time the

excessive heat that passes out of the exhaust will destroy the valves.

It is apparent that for the best results, the spark should occur

slightly before ignition in order to gain the effects of the

compression, and a high working pressure on the piston. It is also

evident that the point of ignition should be varied for different

mixtures that have different rates of burning. With engines that govern

their speeds by throttling or by changing the quality of the mixture it

is necessary for the best results, to vary the point of ignition with

each quality of fuel that is admitted by the governor. The retard and

advance of the ignition is very necessary on an automobile engine

because of the throttling control and constant variation of the load and

speed. All automobilists know of the heating troubles caused by running

on a retarded spark.

(38) Two Stroke Cycle Diagram.

In the two stroke cycle diagram, the lines showing the suction and

scavenging strokes are missing if the indicator is applied only to the

working cylinder.

Starting at the beginning of the working stroke as at A in Fig. 13, the

gas expands during the working stroke until the piston uncovers the

exhaust port at B where the pressure drops to C. A slight travel

uncovers the inlet port with the pressure still above atmosphere due to

the pressure in the crank case filling the cylinder. The crank case

pressure continues from C to D or to the end of the stroke, the pressure

dropping slightly at the latter point.

The compression stroke now takes place with the piston moving from right

to left, the compression pressure reaching a maximum at F. Ignition

occurs slightly before the point of greatest compression, at I, and the

expanded gas increases in pressure until the point A is reached. From

this point the same cycle of events is repeated. Because of the dilution

of the charge by the burnt gases of the preceding combustion, the

mixture burns slowly as will be seen from the inclined combustion line

FA. Due to this delayed combustion, the piston travels the distance S on

the working stroke before the pressure reaches a maximum. This diagram

is typical of the small marine type of two stroke cycle engine which has

no further scavenging than that performed by the rush of the entering

mixture. The diagram of the pressures and vacuums in the crank case are

similar to those of suction and compression in the four stroke cycle

type.

(39) Diagram of Diesel Engine.

A diagram of the Diesel engine is different in many particulars from

that of an ordinary gas engine, as will be seen from the diagram in Fig.

14. The pressures rise in an even, gradual line from the end of the

compression curve, and instead of having a sharp peak at the end of the

combustion, as in a gas engine, the top of the curve is broad and

greatly resembles the indicator diagram of a steam engine. The

compression curve constitutes a greater proportion of the pressure line

than that of a steam engine, the rise of pressure due to the ignition

being very slight in comparison to the height of the compression curve.

There is no explosion in the usual sense of the word, only a slight

increase in pressure as distinguished from the rapid combustion in the

gas engine.

Starting at the beginning of the compression stroke at H, the pressure

of the pure air charge increases to about 500 pounds to the square inch

at I, the point at which the fuel is injected. From I to C is the

increase of pressure due to the combustion. The pressure stays at a

constant height from C to D as the fuel supply is continued between

these points, and is cut off when the piston reaches the position D. It

will be seen that the admission of the fuel through the distance A

covers a considerable proportion of the working stroke, and that the

points of fuel injection and ignition are coincident.

From the point of fuel cut-off at D expansion begins and is continued in

the usual manner to F, the point of release.

When the load is increased, the period of oil injection is also

increased, the other events remaining constant. Should the light load

require an oil injection period as shown by A, the greater load would

require injection for the period B. In the latter case, the expansion

line would be EG, which would produce a diagram having a greater area

than the line DF, and there would be a great increase in the release

pressure GH as well.

It will be seen from the diagram that the quantity of air taken into the

cylinder and the compression pressure remain constant with any load, and

that for this reason it is possible to have a constant point of

ignition, or rather point of fuel injection. As there is no mixture

compressed, there are no difficulties encountered at light loads due to

attenuated mixtures. An excess of air over that required to burn the

fuel is also present at every load within the range of the engine. For

the sake of simplicity, the suction and scavenging lines on the Diesel

engine have been omitted, but they are the same in all respects as the

corresponding lines shown in the diagram, Fig. 14.

(40) Gas Turbine Development.

In the attempt to gain mechanical simplicity, small weight, and

diminutive size of the steam turbine, many able experimenters have

endeavored to obtain an internal combustion motor in which the energy of

the expanding gas is converted into mechanical power by its reaction on

a bladed wheel, but so far the problem is far from being solved. In 1906

two experimental turbines were built by René Armengand and M. Lemale, of

the constant pressure type, one of which developed 30 Brake horse-power

and the other 300 horse-power.

A 25 horse-power De Laval steam turbine was altered by Armengand says

Dugald Clerk so that it operated with compressed air instead of steam.

The compressed air was passed into a combustion chamber together with

measured quantities of gasoline vapor, and the mixture was ignited by an

incandescent platinum wire as it entered the chamber, thus maintaining a

constant pressure with continuous combustion. Around the carborundum

lined combustion chamber was imbedded a coil in which steam was

generated by the heat of the burning gas, the steam being used to reduce

the temperature of the gas from 1800°C to about 400° as it issued from

the orifice and came into contact with the running wheel. The working

medium was therefore composed of two elements, the products of

combustion and the steam at the comparatively low temperature of 400°C.

The constant pressure maintained in the combustion chamber was about 10

atmospheres, and the hot gases were allowed to expand through a conical

Lava jet in which the expansion produced a high velocity, and reduced

the temperature of the fluid. At this reduced temperature and high

velocity the gases impinged upon the Laval wheel, and rotated the wheel

in the same way as steam would have done. The experiments showed that

under these conditions the total power obtained from the turbine

separate from the compressor was double that necessary to drive the

compressor.

In the large 300 H. P. turbine the first part of the combustion chamber

was lined with carborundum, backed by sand, but the second part was

surrounded by a coil through which water was circulated. The water kept

the temperature of the combustion chamber within safe limits, and after

absorbing heat, it passed also around the jet nozzle, and was discharged

into the passage leading to the jet, and there converted into steam by

the hot gases. A mixture of products of combustion and steam thus

impinged upon the turbine wheel. The expanding jet was arranged to

convert the whole of the energy into motion before the fluid struck the

wheel; the temperature was thus reduced to a minimum before the gases

touched the blades. Notwithstanding this, the wheel itself had passages

through which cooling water flowed, and each blade was supplied with a

hollow into which water found its way. In the large turbine the

compressor was mounted on the turbine spindle; it was of the Rateau

type, and consisted of an inverted turbine of four stages, which

delivered the compressed air finally to the combustion chamber at a

pressure of 112 lb. per sq. in. absolute. The efficiency of this turbine

compressor was found to be about 65 per cent. The total efficiency of

the combined turbine and compressor was low, as the fuel consumption

amounted to nearly 3.9 lb. of gasoline per B. H. P. hour. An ordinary

gasoline engine with a moderate compression can readily give its power

at the rate of 0.5 lb. of gasoline per B. H. P. hour. The combined

turbine and compressor was stated to have run at 4,000 R. P. M. and to

have developed 300 H. P. over and above the negative work absorbed by

the compressor.

A gas turbine in which there was no compression was built in the

following year by M. Karovodine which gave 1.6 horsepower at a speed of

about 10,000 revolutions per minute.

It contained four explosion chambers having four jets actuating a single

turbine wheel, which wheel was of the Laval type, about 6 inches

diameter, having a speed of 10,000 R. P. M. The explosion chambers were

vertical, and had a water jacket surrounding the lower end. The upper

portion contained the igniting plug on one side, and the discharge pipe

connecting with the expanding jet on the other. In the lower

water-jacketed part there was provided a circular cover, held in place

by a screwed cap. This circular plate was perforated with many holes,

and it carried a light steel plate valve of the flap or hinging type,

which pulled down by a spring contained within the admission passage.

This spring could be adjusted, and the lift of the valve was regulated

by means of a set screw passing diagonally through the water jacket. Air

was admitted at one side by a pipe leading into the valve inlet chamber

and a corresponding passage or pipe admitted gasoline and air or gas to

mix with the air before reaching the thin plate valve. Adjusting

contrivances were supplied in both air and fuel ducts. To start the

apparatus, an air blast was forced through the valve, carrying with it

sufficient gasoline vapor to make the mixture explosive. The electrical

igniter was started, and the spark kept passing continuously. Whenever

the inflammable mixture reached the upper part of the combustion chamber

ignition took place, and the pressure rose in the ordinary way, due to

gaseous explosion. The gases were then discharged through the pipe and

nozzle on the Laval wheel. The cooling of the flame after explosion and

the momentum of the moving gas column reduced the pressure within the

explosion chamber to about 2 lb. per sq. in. below atmosphere. Air and

gasoline vapor then flowed in to fill up the chamber, and as soon as the

mixture reached the igniter, explosion again occurred. In this way a

series of explosions was automatically obtained, and a series of gaseous

discharges was made upon the turbine wheel. Diagrams taken from the

explosion chamber showed a fall in pressure during suction of 2 lb. per

sq. in.; ignition occurred while the pressure was low, and the pressure

rapidly rose to about 1 1–3 atmospheres absolute. The pressure

propelling the gas column and jet was thus only 5 lb. per sq. in. above

atmosphere. The pressure rapidly fell, and the whole process was

repeated again. According to the diagrams taken, a complete oscillation

required about 0.026 second, so that about 40 explosions per second were

obtained.

[Illustration:

Fig. 15. Cross-Section of the Combustion Chamber of the Holzwarth Gas

Turbine. From the Scientific American.

]

The most promising type of turbine that has been built to date is that

turbine field. A 1000 horse-power machine has been built at this writing

and as experimental machines go has made most remarkable performance.

The turbine in general arrangement outwardly resembles the Curtis steam

turbine, in that the turbine wheel rotates in a horizontal plane, the

spindle or shaft is vertical and a dynamo is mounted on this spindle

above the turbine. In the Holzwarth turbine ten combustion chambers are

provided, each of a pear or bag shape. They are arranged in a circle

around the wheel, and are cast so as to form the base of the machine.

The wheel is of the Curtis type, with two rows of moving and one row of

stationary blades.

In this turbine the energy of the fuel is liberated intermittently by

successive explosions, instead of by continuous combustion, and in much

the same way that the explosions occur in a reciprocating engine. Tests

made on the new machine have shown that it is in no way inferior in

efficiency to the ordinary type of motor, and that at full load, the

weight per horse-power is only about one-quarter of that of the

reciprocating engine. The weight factor, as is well known, is of the

utmost importance in marine service and should prove of value to the

marine engineer, if this alone were its only characteristic.

Any of the ordinary power gases may be used with success, as well as

vaporized liquid fuels, and the lower grade oils such as crude and

kerosene have given much better results in the turbine, than in

reciprocating engines, even at this early stage of its development. As

the heat losses are much smaller than met with in ordinary practice, the

temperature is higher, which, of course, greatly facilitates the

vaporization of the lower grade liquids.

Mr. Holzwarth does not give the dimensions of his turbine wheel, but

from the drawings and some of the velocities given by him it appears to

be about 1 m. in external diameter. The lower part of each combustion

chamber carries gas and air inlet valves, and the upper part carries a

nozzle arranged to cause the gases to impinge upon the first row of

moving blades. This nozzle is connected to and disconnected from the

combustion chamber by means of an ingeniously operated valve. The

explosion chambers are charged with a mixture of gas and air, which

appears to attain a pressure of about two atmospheres within the chamber

before explosion. The air and gas are supplied under sufficient pressure

from turbine compressors, actuated by steam raised from the waste heat

of the explosion and the gases of combustion, so that whatever work is

done in compression is obtained by this regenerative action, and does

not put any negative work upon the turbine itself. The combustion

chambers are fired in series, by means of high-tension jump spark

ignition.

Referring to the cut, the explosion chamber A is filled intermittently

with the explosive mixture at a low pressure (about 8 to 12 pounds per

square inch). When ignition has occurred, the pressure of explosion

opens the nozzle valve F, allowing the compressed gases to flow through

the nozzle G to the bladed turbine H, on which the energy is to be

expended. The expansion of the heated gases in the nozzle reduces the

pressure to that of the exhaust, with the resulting increase in the

velocity of the gas. By means of fresh air, the nozzle valve F is kept

open throughout the expansion and scavenging periods.

After the expansion has been completed, the air that is forced through

the valve D, at a low pressure, thoroughly scavenges or removes the

residual burned gases left in the combustion chamber and nozzle, forcing

it into the exhaust. When the scavenging has been completed, the nozzle

valve and the air valve D are closed. The combustion chamber A is now

filled with pure cold air, which not only enables a fresh charge of gas

to be introduced into the chamber but which also aids in keeping the

chamber cool.

Pure fuel gas, or atomized oil, is now injected through the fuel valve

E, forming an explosive mixture ready for the ensuing cycle of events. A

number of these chambers are arranged around the turbine wheel in order

to have a uniform application of power, by having the several chambers

working intermittently. This is in effect, the same proposition as

increasing the number of cylinders on a reciprocating engine.

CHAPTER V

TYPICAL FOUR STROKE CYCLE ENGINES

(41) Essential Parts of the Gas Engine.

On all gas engines of accepted type are found certain devices necessary

for the performance of the events or cycles outlined in the preceding

section.

For the sake of simplicity these devices are treated as a part complete

in itself. The details of construction, and the refinements found

necessary in the actual construction will be described in the succeeding

chapters.

The names and purpose of these essential components, and their relation

to the operation of the engine as a whole, will be found in the

following outline:

1. The =CARBURETOR= is a device whose purpose is to vaporize the liquid

fuel, and mix the vapor thoroughly and in correct proportions with the

air required for the combustion, in the engine cylinder.

The combustible mixture thus formed is drawn into the cylinder of the

four stroke cycle engine or into the crank chamber of the two stroke

cycle engine.

=GENERATOR VALVES= or =MIXING VALVES= are similar to the carburetor in

principle but are slightly different in detail.

2. The =CYLINDER= is the containing vessel in which the combustion and

expansion of the gas takes place.

The cylinder as its name would suggest has a circular opening or bore

extending from end to end, the bore being smoothly finished to receive

the reciprocating piston.

3. The =PISTON= is a plunger or movable plug fitting the bore closely

enough to prevent the escape of gas, but at the same time is capable of

sliding freely to and fro.

When pressure is established in the cylinder from the combustion,

pressure is also exerted on the end of the piston tending to force it

out of the cylinder. The extent of this force is governed by the area of

the end of the piston and also by the pressure of the gas.

Thus the purpose of the piston is to convert the pressure of the

expanding gas into direct mechanical force, and also to transform the

increasing volume of gas into motion. Another, and no less important

function of the piston is to compress the combustible gas in the upper

end of the cylinder for ignition.

[Illustration:

Piston and Connecting Rod of the Sturtevant Aero Motor, Showing Three

Piston Rings.

]

4. The =CONNECTING ROD= (Sometimes called the Pitman) transmits the

pressure on the piston to the crank, the connecting rod being the means

through which the to and fro motion of the piston is transmitted into

the rotary motion of the crank; its action being similar to that of the

human arm turning the crank of a pump or windlass.

5. The =CRANK= receives the pressure and motion of the piston from the

connecting rod, changing the reciprocating motion of the piston into the

rotary motion required by the machinery which the engine drives.

In the majority of cases the crank revolves, while the cylinder stands

still, but in some of the recently developed aeronautic motors this is

reversed, the cylinders revolving with the crank stationary. The

relative motion, however, is the same in both cases.

(6.) The =CRANK SHAFT=, of which the crank is an integral part,

transmits the rotary motion of the crank to the driving pulley.

(7.) The admission and release of the gases to and from the cylinder are

controlled by the =INLET VALVE= and =EXHAUST VALVE=, respectively, in a

four stroke cycle engine.

The valves are merely gates, allowing the gas to flow, or stopping it,

at the proper intervals, depending on the event taking place at that

time in the cylinder.

In the two stroke cycle engine there are no valves, the admission and

release of the gas being controlled by the position of the piston, and

the openings cut in the cylinder walls.

6. =IGNITION= or the firing of the combustible charge is accomplished by

the =IGNITION SYSTEM=. In most modern engines the mixture is ignited

when it is under the greatest pressure or at the end of the stroke.

For maximum efficiency the mixture should be ignited when it is under

the greatest pressure or compression. The time at which ignition occurs

is also controlled by the ignition system.

7. The =GOVERNOR= regulates the speed of the engine; either by changing

the richness of the mixture, by changing the number of working strokes

in a given time or by altering the quantity of gas admitted to the

cylinder, or sometimes by a combination of these methods.

8. The =BELT WHEELS= or =PULLEYS= are the means of transmitting the

power of the engine to the work to be performed. The engine is generally

connected to the driven machinery by a belt connecting the engine pulley

with the pulley of the driven machine.

9. The =FLY WHEELS= by reason of their mass and their momentum, store up

a portion of the energy expended during the working stroke, and return

it to the engine in order to carry it through the idle strokes of

compression, admission and expulsion. In some engines the fly wheels

serve in double the capacity as pulleys.

10. The =BASE= or =FRAME= of the engine acts as a foundation for the

various working parts, holding them in their proper positions.

(42) Application of the Four Stroke Principle.

While the five events of every commercial four stroke cycle engine are

accomplished in exactly the same order, or routine as explained in

paragraph (8), Chapter 3, the actual design and method of applying the

cycle varies greatly in different makes of engines. This great

difference in the details of construction often makes it difficult for

the novice to identify the cycle of operations in that particular

engine. The different forms of valve gears that are used to perform the

same functions in the cycle are good examples of the variation in

design, some makers using the poppet or disc type, some the sliding

sleeve, and others the rotary type.

[Illustration:

Fig. 16. Ball Bearing Crank Shaft, Pistons and Connecting Rods of the

“Maximotor,” in Their Relative Positions.

]

Multiple cylinder engines vary in the cylinder grouping or arrangement,

the arrangement and number of cylinders depending on the service for

which the engine is intended, the amount of vibration permissible, or

the weight. The question of speed also introduces modifications in the

design, but no matter what valve arrangement is adopted or what grouping

of cylinders is used, a four stroke cycle engine performs the five

events of suction, compression, ignition, expansion and exhaust in four

strokes, in each and every cylinder. With the exception of fuel

injection (which in reality corresponds to the ignition event) in the

four stroke Diesel engine, the indicator cards of all four stroke cycle

engines passes the same characteristics as the diagram shown in Fig. 10.

In this chapter, the engine will be described without regard to the fuel

used, or to the means adopted in vaporizing it, for the vaporizing

appliances are considered as being external to the engine proper, except

in some of the heavy oil engines, and as the fuel is gasified before

entering the cylinder the question of fuel does not affect the general

construction of the engine. The majority of engines are readily

converted from gasoline to gars, or in some cases kerosene, by changes

in the vaporizing device, and with the exception of changing the

compression pressure, little further alteration is needed. Since the

vaporization and admission of the heavier oils, such as crude oil and

kerosene has a more intimate relation to the engine than the use of

gasoline or gas, the heavy oil engines will be described in a separate

chapter in order that the process of oil burning may be more fully

explained. It should not be understood that the cycle, or principle of

the oil engine differs from that of any other engine, but that the

vaporizer forms such a close connection with the engine proper that they

must be described as one unit.

(43) Horizontal Single Cylinder Engine.

An example of a modern single cylinder engine operating on the four

stroke cycle principle is the “Muenzel” engine shown in Section by Fig.

17. It is of the single acting type, that is, the pressure of the gases

acts only on the left end of the piston which reciprocates in a

horizontal direction. Surrounding the cylinder in which the piston

slides, is the water jacket (shown by the short horizontal dashes) which

keeps the cylinder walls from becoming overheated by the successive

explosions of the mixture. The cooling water is pumped into the jacket

through the pipe shown over the cylinder, and flows out of the jacket

through an outlet near the bottom of the cylinder.

[Illustration:

Fig. 17. Longitudinal Section Through the Muenzel Horizontal Engine.

]

Both the inlet and exhaust valves are situated in an extended portion of

the combustion chamber to the left of the piston, the upper valve being

the inlet and the lower valve, the exhaust. The valves are held on their

seats by means of coil springs that act on the upper ends of the valve

springs. Admission of the explosive mixture is controlled by the upper

valve, and the release of the burnt gases by the lower. Pipes at the

bottom of the cylinder marked “Gas Supply” and “Exhaust” convey the

gases to and from the inlet and exhaust valves respectively.

[Illustration:

Fig. 18. Elevation of Muenzel Engine Showing Lay Shaft and Valve

Connections.

]

The inlet valve, and the inlet valve spring are held in one unit by a

removable metal housing known as a “Valve Cage”, which is arranged so

that the cage, valve, and spring may be removed as one piece from the

cylinder casting when the valves need attention by removing a few bolts.

As the cage is directly over the exhaust valve, and is considerably

larger in diameter, it is possible to remove the exhaust valve through

the opening left by the removal of the inlet valve cage. Both valves are

surrounded by a water jacket, as are the passages that lead to them.

Both the inlet and exhaust valves are opened and closed at the proper

moments in the stroke by means of cams mounted on the horizontal cam

shaft shown by Fig. 18 through a system of levers. The cam shaft is the

shaft running parallel to the engine bed from the crank-shaft to the end

of the cylinder and turns at one-half the speed of the crank-shaft. At a

point directly below the inlet valve in Fig. 18, will be seen an

enlargement on the shaft on which rests the rod running from the inlet

valve to the cam shaft. This is the cam.

A cylindrical casing shown above the cylinder contains the governor

which maintains a constant speed at all loads by operating a valve in

the intake pipe which varies the quantity of mixture entering the

cylinder in proportion to the load. The governor is driven from the

cam-shaft by spiral gears. The igniter which furnishes the spark for

igniting the gas is located between the two valves at the extreme left

of the combustion chamber (Fig. 17).

It should be noted that the cylinder head which closes the left end of

the cylinder, and which carries the valves is separate from the main

body of the Cylinder. By unscrewing the bolts that hold it to the

cylinder, the head may be removed when it becomes necessary to remove

dirt and carbonized oil from the combustion chamber, or when it becomes

necessary to remove the piston. The cylinder barrel in which the piston

works may also be removed through the opening left by the piston head

when it becomes worn, and another barrel or liner may be substituted,

thus practically renewing the engine at a small fraction of the cost of

a new cylinder. The liner is fastened firmly to the outer cylinder

casting at the left but is free to slide back and forth in the casting

at the right hand end, this end being provided with a packed joint. This

play given to the liner allows it to expand and contract freely with the

different changes of temperature without causing strains either in the

cylinder or in the liner.

(44) Multiple Cylinder Engines.

Since the power exerted by a single cylinder four stroke cycle engine is

intermittent, the explosive force exerted on each power stroke is much

heavier than would be the case if the power application were continuous,

as the explosions must be heavier to compensate for the idle periods. To

reduce the strain on the engine and the vibration as well and to obtain

an even turning moment it has been customary to provide more than one

cylinder on engine of over 10 horse-power capacity. In this way the

total power is divided among a number of cylinders, and as no two

cylinders are under ignition at any one time the turning moment is more

even, the vibration is less, and the strain on the engine is

considerably reduced.

Dividing the power in this way makes it possible to reduce the weight of

the engine as less material is required to resist the strains and a

small fly-wheel may be used because of the even engine torque. In order

to gain the full benefit of this reduction in weight, the builders of

aeronautic motors have carried the multiplication of cylinders to an

extreme, the Antoinette for example having sixteen cylinders. Engines

having more than six cylinders exert a continuous pull as the impulses

“overlap,” that is, ignition occurs in one cylinder before another

cylinder in the series ends its working stroke. The greater the number

of cylinders, the more continuous will be the torque or turning moment.

The multiple cylinder engine may be considered as a group of single

cylinder engines connected together, and receiving their fuel from a

common source, the only difference between the single and multiple being

in the inlet and exhaust piping and the ignition system.

[Illustration:

Fig. F-12. Six Cylinder Maximotor.

]

[Illustration:

Fig. F-13. Four Cylinder Buffalo Motor for Marine Service.

]

As a single cylinder four stroke cycle engine has one working impulse in

every two revolutions, a two cylinder engine will have an impulse for

every revolution as there are twice as many impulses in the same time.

It should be remembered that the number of impulses given per revolution

by a four stroke cycle engine is equal to the number of cylinders

divided by two. Thus, a six cylinder engine has 6 ÷ 2 = 3 impulses per

revolution, and an eight cylinder, 8 ÷ 2 = 4 impulses, providing of

course, that the engine is single acting.

Arrangement of the cylinders varies with the service for which the

engine is intended and the perfection of balance that is required, the

principal arrangements being the “V,” the “upright,” the opposed, the

“radial,” “tandem,” and “twin.” The upright engine has the cylinders all

on one side of the crank-shaft in a straight line, as in the four

cylinder automobile engine. In this form, each cylinder has an

individual crank throw the number of throws being equal to the number of

cylinders. This engine is fairly well balanced in the four, six and

eight cylinder types, as one-half of the connecting rods and throws are

up, while the other half are down, but as the connecting rods do not all

make equal angles with the center line of the cylinder at the same time

there is a slight unbalance in the four and six cylinder types. Because

of the ignition sequence, two cylinder vertical motors are in no better

balance than the single cylinder type since both crank throws and

connecting rods are on the same side of the shaft at the same time. For

this reason the two cylinder engine is most commonly built in the

opposed type which gives perfect balance.

In “V” type arrangement, one-half of the cylinders are set at an angle

of about 90° with the rest of the cylinders, or in the two cylinder “V”

the cylinders are set in the same plane, perpendicular to the shaft, at

angle varying from 57½° to 90°. The “V” type arrangement is adopted

where light weight and compactness are the principal requirements, as

the weight and length are both reduced by putting the cylinders opposite

to one another by pairs, the “V” being practically one-half the length

of an upright having the same number of cylinders. This arrangement

permits the use of one-half the number of crank throws used in the

vertical type as each crank throw acts for two cylinders. For the reason

that both the cylinders of a two cylinder “V” act on a common crank

throw, the two cylinder “V” is in no better balance than a single

cylinder engine.

[Illustration:

Fig. 18-a. G. H. H. Double Acting Tandem Cylinder Engine (German). It

will be Noted that an Inlet and Exhaust Valve Are Placed at Both

Ends of Each Cylinder. The Exhaust Valves Are Below and the Inlets

Above the Cylinders. As this Engine is of the Four Stroke Cycle

Type, Each Cylinder Gives One Impulse per Revolution, or Two

Impulses per Revolution for Both Cylinders. The Piston and Piston

Rod Are Both Cooled by Water, and Are Supported by the Cross Heads

so that Their Weight is Taken Off the Cylinder Bore.

]

An “opposed” type engine is in the most perfect mechanical balance of

any engine as the crank shafts and connecting rods are not only on

opposite sides of the crank-shaft, but make equal angles with the center

line of the cylinders as well, at all points in the revolution. The

explosive impulses occur at equal angles in the revolution as in the

four and six cylinder vertical type. An opposed engine may be considered

as a “V” having a cylinder angle of 180°. In the opposed type, one crank

throw is provided for each cylinder, the pistons of the opposite

cylinders traveling in opposite directions at the same time.

A “radial” or “Fan” type motor, as the name would suggest has the

cylinders arranged in one or two rows around the crank case, each

cylinder being on a radial line passing through the center of the

cylinder with one crank throw for each row. The Gnome engine illustrated

elsewhere in the book is an example of this type, the seven equally

spaced cylinders acting on a common crank throw. When more than seven

cylinders are used on this engine, as in the fourteen cylinder engine,

two cranks are provided, each crank serving seven cylinders. This

arrangement cuts down the weight of a motor enormously because of the

short crank shaft and case. With the ignition properly timed and the

cylinders correctly spaced the firing impulses occur at equal angles.

“Tandem” cylinders are employed only on stationary engines, the

cylinders being placed on the same center line, one in front of the

other, and when this arrangement is adopted it is the usual practice to

make the cylinders double acting. The two pistons are connected by a rod

known as the “piston rod” which extends from the rear end of one

cylinder into the front of the following cylinder. Tandem cylinders

require too much room for use on automobiles or motor boats, and for

this reason are seldom seen in this service.

The “twin” engine is a modification of the vertical cylinder

arrangement, both cylinders being on the same side of the shaft and in

line with one another. It is the type most generally used on very large

stationary engines that have more than one cylinder, and instead of

being vertical as in their prototype are generally laid horizontally.

Since the twin engine is generally double acting, the crank throws are

placed on opposite sides of the shaft.

(45) Four Cylinder Vertical Auto Motor.

A common type of four cylinder vertical motor is shown by Fig. 19, which

is of the type commonly used on automobiles. In order to show the

general construction of the cylinder, each cylinder is cut through at a

different point. The cylinder at the extreme left is shown in elevation,

or as we would see it from the outside. In the second cylinder from the

left, the section is taken through the valve chamber, which projects

from the side of the cylinder. A section through the center of the

cylinder is shown on the third cylinder, and the fourth cylinder is in

elevation.

On cylinder No. 1, (left) is seen the exhaust pipe (32) and the inlet

pipe (31) entering to valve chamber and connected to the exhaust valve

and inlet valve respectively. The pipes are held in place by the clamp

or “crab” (33). The exhaust pipe connects with the exhaust valve of each

cylinder, and terminates at the fourth cylinder as shown by (32).

Screwed into the top of the valve chamber on cylinder No. 1 are the two

spark plugs (34) and the relief cock (35).

Referring to cylinder No. 2, the inlet valve (42) is shown at the left

of the chamber and the exhaust valve also shown by (42) is shown at the

right. Above the valves are the spark plugs (34) which project into the

space above the valves. Pressing against the lower ends of the valve

stems and holding the valves tight on their seats are the springs (44)

which fit into the washers (45) fastened to the stems. The valve stems

terminate in a nut at (48). The valve stem guides (43) form a support

for the valves and at the same time form an air tight connection for the

stems to slide in.

Immediately beneath the stems are the push rods (46) which are provided

with an adjustment (48) at the upper end, and a roller (49) at the lower

end. The rollers (49) rest directly on the cams mounted on the cam shaft

(27), and as the irregular cams revolve, the push rods are moved up and

down which in turn act on the valve stems and raise the valves at the

proper moment. The cams raise the valves and the springs close them. The

two cams (exhaust and inlet) appear as two rectangular enlargements on

the shaft (27). The bearings (53), support the cam shaft, one being

supplied for each cylinder.

At the extreme left of the crank shaft is shown the half time gear (20)

which meshes with the gear on the crank-shaft and drives the cams. Next

to this gear is the large cam shaft bearing 26. It should be noted that

the section through the valve chamber taken on cylinder No. 2 is at a

point considerably back from the center line of the cylinders and not in

the same plane as the section shown on cylinder No. 3, which is taken

through the center line of the cylinders.

[Illustration:

Fig. 19. Cross-Section Through Typical Four Cylinder Automobile

Engine. Courtesy of the Chicago Technical College.

]

In the section of cylinder No. 3, we see the water space surrounding the

upper portion of the cylinder with the opening (37) connected to the

water manifold (36), through which the water leaves the cylinder and

passes to the radiator. At the lower end of the stroke is the piston,

one-half of which is shown in section and one-half in elevation so that

internal and external appearance may be readily seen. The piston pin

(60) is located approximately in the center of the piston to which it is

secured by means of the set-screw (61).

By means of the connecting rod (56), the motion of the piston is

transmitted to the crank-shaft throw (54), both ends of which are

provided with bronze bushings (59) and (58), fitting on the piston pin

and crank-pin respectively. Between each crank throw are the main crank

shaft bearings (55) which are provided with the bronze bushings (54).

Below the connecting rod ends is the small drip trough containing oil

into which the pipes on the rod ends dip when passing around the lower

end of the stroke. When the pipes enter the oil puddle a small amount of

lubricating oil is driven into the crank-pin bearing because of the

force of impact, this force also causing oil to splash about in the

crank case for the lubrication of the main crank shaft bearings and cam

shaft. In order to maintain a constant level of oil in the puddle so

that the bearings shall receive a constant supply of oil, a small

overflow opening is placed in the center of the puddle which allows an

excess of oil to overflow into the return oil sump below.

This excess of oil drains by gravity back to the oil circulating pump

(73), at the right which again forces the oil to the various bearings.

In this way, the same oil is used over and over again until it becomes

unfit for lubricating purposes because of dirt or decomposition. The oil

pump is driven from the cam-shaft through the level gears (66) and the

vertical shaft (72). To the right of the oil pump is the fly-wheel (75)

which furnishes the power for the idle strokes of the engine.

At the upper end of the vertical shaft that drives the oil pump is an

extension (68) which passes through the bearing (70) and drives the

ignition timer shown at the top of the housing (69). The timer controls

the period of ignition in the cylinders in regard to the piston position

so that the spark occurs at the end of the compression stroke. At the

extreme left of the engine is the radiator fan (1) which is driven from

the crank-shaft pulley (16), the belt (10), and the fan pulley (1122).

This fan increases the amount of cold air that is drawn through the

radiator, (mounted to the left of the engine) and increases its capacity

for cooling the jacket water of the engine. The water circulating pump

is located on the opposite side of the motor.

[Illustration:

Fig. 19-a. Buda Four Cylinder Automobile Motor. Carburetor Side.

]

[Illustration:

Fig. 19-b. Buda Motor, Pump Side, Cylinders “En Bloc.”

]

In this motor both the inlet and exhaust valves are located on the same

side of the cylinder which arrangement classifies the engine as an “L”

type, the extended valve pockets forming an “L” with the center line of

the cylinder. In the motor shown by Figs. F-14-F-15, the inlet and

exhaust valves are on opposite sides of the cylinder as shown in the

cross-section, which classifies the motor as a “T” type, as the valve

chambers together with the cylinder forms a “T.” The latter type of

motor has several advantages over the “L” type, but as it requires two

cam shafts, one for the inlet and one for the exhaust valves, it is not

adopted by the builders of the cheaper grades of automobiles. Since the

exhaust valves are on the opposite side of the cylinder, in the “T”

type, the inlet air is not expanded nor the output diminished by the

heat of the exhaust passages. The piping is less complicated which

permits of a more effective arrangement of the carburetor and magneto.

Since the piping in the latter type can be arranged to better advantage,

less back pressure is the result.

[Illustration:

Fig. F-14. Cross-Section Through Wisconsin Truck Motor. “T” Type.

]

[Illustration:

Fig. F-15. Longitudinal Through Wisconsin Truck Motor.

]

As in the previous case, the valves are acted on directly by the cams

and push rods, one cam shaft being provided on each side of the

cylinders. In order to reduce the noise made by the push rods and

springs, all of the springs are enclosed by sheet metal housings or

tubes. The circulating pump is shown at the left nearly on a line with

the left hand cam shaft, the pump outlet being inclined toward the

cylinder so that it enters the water jacket under the exhaust valves.

Water leaves the jacket by the pipe shown on the cylinder tops.

From the longitudinal section it will be seen that the cylinders are

cast in pairs, two cylinders to the pair, instead of singly as in the

previous case. The large pipe crossing at about the center of the

cylinders is the exhaust pipe (shown in front of the left pair), and the

pipe shown under the exhaust is the water inlet pipe from the

circulating pump. It will be seen from the longitudinal section that the

main crank-shaft bearings are fastened to the upper half of the crank

case, and are entirely independent of the lower half which acts simply

as an oil shield. This construction allows the oil shield (lower half)

to be removed without disturbing the adjustment of the bearings, when it

becomes necessary to inspect the internal mechanism.

[Illustration:

Six Cylinder Rutenber Automobile Motor, with Cylinders Cast in Pairs.

]

Large removable plates cover the top of the water jackets so that it is

a simple matter to clean out the water space in case that it becomes

coated with deposits from the water. This is an important feature as a

great many of the heating troubles may be overcome by having access to

the interior of the water jacket. The water outlet pipes connect with

the jacket covers. Both cam shafts are driven by the gears at the right

which connect with the crank shaft pinion. Fan is belt driven from an

extension to the cam shaft.

All bearings are supplied with oil by a high pressure force feed pump,

the crank pins receiving their supply through channels drilled in the

crank shaft and pin, which in turn are connected to the oil supply of

the main bearings, no dependence being placed on a splash system. After

leaving the bearings, the oil drops into the crank case and drains into

the sump shown at the left of the longitudinal section. From the sump,

the oil returns to the oil pump from which point it is returned to the

circulating system under high pressure.

(46) Stationary Four Cylinder Engine.

An English stationary engine, the Browett-Lindly, similar in many

respects to the automobile engines just described, is shown in

longitudinal and cross-section by Figs. 20 and 21. This is of the “L”

type of valve arrangement, but instead of having the valves side by side

as in the preceding case, the inlet valve is placed over the exhaust as

will be seen from the cross-section view.

[Illustration:

Fig. 21. Cross-Section Through Browett-Lindly Engine.

]

The exhaust valve is operated directly from the cam shaft by the push

rod as in the auto engines, but the inlet valve receives its motion

through a long vertical rod and horizontal lever, the latter being

located on the cylinder head as shown by the longitudinal section. A

supplementary valve is mounted loosely on the stem of the inlet valve,

and this valve is held against the seat of the gas inlet port by a short

spring.

[Illustration:

Fig. 20. Section Through Browett-Lindly Four Cylinder Stationary

Engine.

]

A collar on the main valve spindle opens this gas valve, and, by

adjusting the position, a certain amount of lag can be given, so that

air first enters the cylinder and then, by further travel of the main

valve, the gas valve opens and the combined charge is taken in. This

prevents any “back fires” as the gas and air are entirely separated

until they enter the cylinder.

Starting is effected by means of compressed air, and is entirely

automatic. No compression release is provided, as this is unnecessary

under the system adopted. By opening the main compressed air valve

compressed air is admitted to two valve boxes placed underneath the cam

shaft, and the pressure of air raises the valves against their levers

and cams. Should the swell on the cam be opposite a lever as it will be

in the correct starting position, the valve cannot close, and the

compressed air then passes to the cylinder through a check valve on the

face of the cylinder, and the engine starts. The automatic check allows

the cylinders to take in a charge of mixture on the second stroke and

firing takes place immediately. When the explosion pressure is greater

than the air pressure the check remains closed and no more starting air

enters the cylinder.

[Illustration:

Fig. 21-a. Section Through Cylinder of Fairbanks-Morse Type “R E”

Engine, with Valves in the Head.

]

Governing is effected by varying both the quantity and quality of the

mixture.

The main valve, plunger, and rod springs, and all springs on the valves

and valve motion, are arranged to be in compression. The exhaust valves

are of cast-iron, and are fitted with renewable seats in the cylinders.

The admission valves are of nickel steel, and are arranged in boxes,

which, when removed from the cylinders, provide the ports which give

access to and space for the removal of the exhaust valves which are

withdrawn vertically.

Forced lubrication is fitted throughout all bearings, valves, plunger

guides, governor, cam shaft, etc., the oil under pressure being supplied

by two valveless pumps, either of which is sufficient to maintain the

working pressure of oil.

The normal output of the engine is 400 brake horse-power, with an

allowable overload of 40 horse-power for ½ hour. The exhaust pipe is

water jacketed, each section being supplied from the small pump shown at

the end of the cross section.

Double ignition is provided for an emergency, by two high tension

magnetos, each of which is connected to a separate set of plugs. When

starting the engine, an ordinary spark coil and storage battery are used

until the engine gets up to speed, when the coil is cut out and the

magneto is thrown in.

(47) The “V” Type Motor.

An example of the “V” type motor is shown by Fig. 22, which is a front

elevation of the Frontier aeronautic motor, a type that occupies a

minimum of space with a minimum of weight.

[Illustration:

Fig. 22. End Elevation of Frontier 8 Cylinder “V” Type Motor.

]

The cylinders are cast separately and are furnished either with iron or

copper water jackets, the copper jackets being deposited over the

cylinder barrels by an electrolytic process in much the same way as that

of the celebrated French Antoinette. Bolts passing through flanges on

the bottom of the cylinder fasten them to the base. A special aluminum

alloy is used for the base which is cast in a single piece with webs to

receive the bearings. A unit crank-case insures perfect alignment,

prevents a greater part of the oil leakage, and forms a much stronger

construction than the usual split pattern. A chamber is provided for the

cam shaft at the apex of the case through which issue the push-rods.

Shafts and piston pins are hollow. All push rods are adjustable for wear

and have steel balls running on the cams which eliminate the possibility

of mis-timing through wear.

Lubrication is by a bronze pump geared from the crank-shaft and is

connected to an oil tank located in the base from which the oil is

forced through the crank-shaft up through the hollow connecting rods to

the piston pins, thence to the cylinder walls, the surplus returning to

the tank in which the strainer is located.

The circulating pump is driven from the cam shaft as shown in the cut

and supplies the cylinders and radiator with water through the copper

water manifolds which are designed to give an equal supply to each

cylinder. Exhaust manifolds are of seamless steel tubing.

The cylinders are 4⅛ bore × 4⅜ stroke, and develop 60 to 70 horse-power

at 1,100 revolutions per minute, which speed has been attained with an

8-foot 6-inch propeller having a pitch of 5 feet. Without radiator or

propeller, the iron jacketed motor weighs 312 pounds, and copper

jacketed weighs 290 pounds, the latter making a difference of 22 pounds

in the weight.

A high tension Bosch magneto is used which is mounted on a pad cast on

the top of the crank-case and is driven from a gear meshing with the cam

shaft gear. Connection is made from the magneto to plugs placed over the

inlet valves in the valve caps.

A 100 horse-power aero engine of the “V” type is shown by Figs.

23–24–25, which is built by the All British Engine Company for the

aeronautical branch of the English War Department. It has eight

cylinders of 5 inch bore, by 4¼ inch stroke, and develops its rated

horse-power at 1,200 revolutions per minute. _Data from “Aero,” London._

[Illustration:

Fig. 23. Longitudinal Section Through A. B. C. 100 Horse-Power “V”

Motor.

]

The crankshaft, which is of three per cent nickel chrome steel, having

an ultimate tensile strength of 157,000 lbs. per sq. in., is of

distinctly large diameter, and is carried in plain bearings lined with

white metal. It is provided with four throws, each crank pin being

arranged to take the big end bearings of two connecting rods from

cylinders on opposite sides of the crank case. There is a bearing

between each throw, and in order to reduce the overall length of the

engine the cylinders are staggered on the crank case. The H section

connecting rods are stamped out of steel having a tensile strength of

90,000 lbs. per sq. in., and for the purpose of lubrication a hole is

drilled from end to end down the center of the web. As mentioned before,

the cylinders are staggered, and there is no overhanging of the big end

bearings at the point of attachment to the connecting rod. The bearings

themselves are lined with white metal. The small end bearings are

provided with phosphor bronze bushes, and the piston pin is of steel

bored out hollow and hardened.

[Illustration:

Fig. 24. Valves and Valve Motion of A. B. C. Motor. (“_Aero_,”

London.)

]

A very interesting detail of the engine is the combination of the water

outlet pipe from the top of the cylinder with the bearings for the

rocking arms (which are steel stampings) actuating the valves. This is

shown in Fig. 25. A hollow steel column is bolted to the top of the

cylinder and protrudes from the water jacket, which is fastened to it

with the usual shrunk ring. To this column is attached a hollow T shaped

pipe of phosphor bronze, the column of the T piece forming the outlet

for the water. On one arm of the T piece the exhaust rocker takes its

bearing and on the other the inlet rocker. Each T piece arm is connected

to its fellow on the next cylinder by means of rubber pip.

[Illustration:

Fig. 25. End Elevation of A. B. C. Motor.

]

A small bracket projecting from the T piece forms a saddle on which the

valve spring rests. This is a plain semi-elliptical leaf spring which

works both valves. It is slotted at each end and slightly turned up so

as to engage with a cotter pin passed through a slot in the end of the

valve stem.

The crank case is of rather unusual design, being absolutely circular in

section and machined all over. It is practically a tube with flanged

portions bolted on to form the ends. Having no horizontal joints, it is

strong and easily kept oil tight. Three radial arms, with slight webs

and reinforced with steel columns down the center, support each bearing.

The crank case is carried by four feet, which are arranged to

accommodate three different widths of engine bearer. To the fore end of

the crank case is bolted a long conical aluminum nose carrying at its

extremity a compound push and pull ball bearing 6 in. in diameter, which

supports an extension shaft bolted to the crankshaft by means of a

flanged coupling.

[Illustration:

Fig. 24-a. “Sixteen” Cylinder Favata Radial Type Aero Motor,

Consisting of Four Groups of Two Cylinders Per Group. Cylinders are

of the Double Acting Type and are Stationary.

]

At the outer end of this extension is a flange to which the propeller is

bolted, but the arrangement is specially devised to make quick

detachment possible. The boss of the propeller has a hollow hub and is

plate bolted permanently to it by twelve bolts.

The direct nose is interchangeable with a speed reduction gear so that

the propeller can be driven at a lower speed than the engine. Fitting

this gear nose raises the center line of the propeller-shaft some 5¼ in.

The gears are carried on substantial ball bearings, plain bearings being

used also in such a way that they take up the load if the ball bearings

through any cause should fail. The reduction is by means of silent

chains. The arrangement of the gear wheels is plain from the drawing,

and it will be noticed that there is no intermediate wheel between the

crankshaft pinion and the camshaft wheel, which are of steel and

phosphor bronze respectively. A separate gear wheel is provided on the

camshaft for driving the magneto. The water and oil pumps are carried

low down outside the crank case, and are driven by intermediate wheels

at double the engine speed. The shafts are joined together through

Oldham couplings, so that it is possible to remove the pumps separately.

Both these pumps are of the gear type.

The camshaft is made in one piece with the cams, and is hardened, being

drilled out for lightness. It is enclosed in a casing of steel tube,

which is practically separate from the crank case, being attached

thereto at one end by the timing gear case and at the other by a saddle.

The camshaft is carried in six bearings. An interesting point is the

fact that the gear wheels are bolted to flanges on the shafts instead of

being attached by keys. Carried in the tube directly above the camshaft

is a second shaft forming the fulcrum of the rocking arms for the cam

rollers. A very interesting point is the provision of an arrangement for

lifting the exhaust valves. The little rocking arms carrying the rollers

which bear upon the cams are provided with webs, parallel with the

camshaft and between it and the shaft carrying the rockers is a third

shaft, the sides of which normally just clear the webs of the rocking

arms on either side. This shaft is provided with wedge shape pieces

along it, so that by sliding it along the wedges lift the rocking arms

clear of the cams, and thus, through the tappet rods and rockers, the

valves themselves are opened.

[Illustration:

Fig. 26. Mesta Engines on Test Floor.

]

Not the least interesting particular of this engine is the thorough way

in which the lubrication is carried out. Four of the bolts which attach

the caps of the main bearings are prolonged through the bottom of the

crank case, and serve to carry a detachable oil sump which holds

sufficient oil for a run of six hours. As already mentioned, the oil

pump is driven at twice the engine speed, and maintains a pressure of

something like 110 pounds per square inch. It delivers directly into a

straight steel tube placed along the bottom of the crank case, and from

this tube a vertical tubular connection is taken to each of the caps of

the main bearings. The crankshaft and crank pins are hollow, and, as in

the previous engine, in the hollow portions tubes of a slightly smaller

diameter are placed, the tubes being expanded over at the ends, so that

closed annular spaces are formed which are used as lubrication leads.

The lubricating oil passes through the main bearings into these annular

spaces in the shafts, from them to the annular spaces in the crank pins,

and so to the big-end bearings. From the big-end bearings it travels up

the connecting rods to the gudgeon pins. It is interesting to note at

this point that the connecting rods work in slots in the crank case

which just allow sufficient clearance for their travel, in order to

prevent the flooding of oil into the cylinders. A steel-lined oil lead

is taken up to the saddle which supports the tubular camshaft casing at

the propeller end of the crank case. The bearings carrying the camshaft

are cut away at their lower edges clear of the tube so that the oil can

flow along the full length of the casing, the level being sufficient to

allow the cams to dip. Precautions are taken to keep oil from flowing

out of the bearings, and the casing over the gears is specially arranged

to prevent the oil from flooding below.

(48) Mesta Gas Engines.

The Mesta four stroke cycle, double acting gas engine, built by the

Mesta Machine Co., Pittsburgh, is an excellent example of American big

engine practice. Mesta engines are built in sizes from 400 horse-power

up to the largest used, and is built either in tandem or twin tandem

units. While the engine does not differ widely in either principle or

construction from engines of the same size it has several features

worthy of note that are not found on other engines.

Up to the medium sizes, the cylinders are cast in one piece, the largest

cylinders being made in two parts of cast steel with air furnace iron

bushings. The central part of the cylinder is open as will be seen from

the cuts, and is covered with a cast iron split band bolted at the

center line. The valve chambers are located directly opposite one

another on a vertical center line, the inlet valve being at the top and

the exhaust valve at the bottom. This arrangement gives a better

distribution of the mixture, increases the output with given size of

cylinder and equalizes the stresses occasioned by the explosions. As the

engine is double acting in all cases there is one inlet and one exhaust

at each end of the cylinder.

Both the inlet valve and the corresponding exhaust valve on each end of

the cylinder are operated by a single eccentric on the horizontal

lay-shaft shown running below and parallel to the cylinders. The

regulating valves which are controlled by the action of the governor are

perfectly balanced against the pressure in the cylinder which results in

a very small resistance to the governor action, therefore no oil relay

nor similar complications are required. Any of these valves are easily

removed for clearing, a point of great importance when running on a gas

that is laden with tar or other impurities.

[Illustration:

Fig. 27. End View of Mesta Engine.

]

The chrome-vanadium piston rod carries the pistons floating free from

the cylinder walls reducing the wear on the bore, while the piston rings

maintain a gas tight contact with the cylinder walls. Each piston rod is

made in two halves, the joint between the sections being made between

the cylinders at which point the rods are supported by an intermediate

cross-head and guide. Both parts of the rod are interchangeable. The

pistons are made in one casting. As will be seen from the accompanying

cuts the front end of the piston rod is carried by a cross-head which

relieves the pressure on the piston and packing glands.

Speed regulation is performed by the governor by controlling both the

quantity and the quality of the mixture. Independent valves in the gas

and air passages are actuated by the governor according to changes in

the load. This method of control combines all of the good features of

quantity and quality regulation.

Make and break ignition is used, with the igniter trip gear so designed

as to allow all of the igniters to be timed from one lever, or adjusted

independently as the case may require. Each combustion chamber is

supplied with two igniters, one at the top and one at the bottom, which

insures regular and rapid combustion and therefore gives a maximum of

efficiency and reliability.

Compressed air is introduced into the cylinders for starting at a period

corresponding to the power stroke in normal operation. This is

accomplished by cam operated poppet valves located in the air main and

check valves in the cylinders. By this system the engine can be started

and put on full load in less than one minute.

(49) Knight Sliding Sleeve Motor.

The Knight motor was the first four stroke cycle automobile motor to

employ an annular slide valve in place of the usual poppet valve. Its

success has led to the development of several other motors of a similar

type which follow the construction of the original engine more or less

closely. Being free from the slap bang of eight to twelve cam actuated

poppet valves which hammer on their seats at the rate of a thousand

blows per minute, the Knight motor is free from noise and vibration.

Instead of the jumping of a number of small parts, there is only the

slow sliding of the sleeves over well lubricated surfaces. They make no

noise because they strike nothing and can cause no vibration because

they are a perfect sliding fit in their respective cylinders.

Besides insuring noiseless operation, the valves increase the output,

efficiency and flexibility of the motor for they are positively driven

and are not affected in timing by fluctuations in the speed. The wear of

the reciprocating increases the efficiency of the sleeve instead of

destroying it. With poppet valves at high speeds, the valves do not seat

properly in relation to the crank position owing to the inertia of the

valves and to the gradual weakening of the valve springs which delays

the closing of the valves. Carbon also gets on the seats of the poppet

valves and prevents proper closure. These faults cannot exist with

sliding sleeves when they are once set right as they are positively

driven through a crank and connecting rod.

[Illustration:

Fig. 28. Section Through Knight Motor Showing the Sleeves, Eccentrics,

and Automatic Adjustment for Lubrication. Inlet is at the Right,

Exhaust at the Left.

]

At high engine speeds the velocity of the exhaust and inlet gases is

very high in the poppet valve type due to the many restrictions and

turns in the passages which causes back pressure and a considerable loss

of power. With the sliding sleeve type an ideal form of combustion

chamber is possible and the passages to and from the chamber are short

and direct. Very large port areas with a low gas velocity are also

possible. The sleeves are more effectively cooled than the poppet type,

being in direct contact with the water cooled walls for their entire

length. Because of the large port areas, the cylinders receive a full

charge of mixture, and as a result the engine accelerates and gets under

way with remarkable ease.

[Illustration:

Figs. 28–29–30. Showing Sleeve Positions on the Inlet Stroke. (Knight

Motor.)

]

The arrangement of the slide valves, or sleeves, is shown by Fig. 28,

which also gives an idea of the cylinder form, and the location of the

piston. Fitting the engine cylinder closely, one within the other, are

the two sliding valve sleeves, and within the inner sleeve slides the

power piston.

[Illustration:

Figs. 31–32–33. Showing Sleeve Positions on the Exhaust Stroke.

]

Each sleeve has two slots cut in it, one on each side, which form an

outlet and inlet for the exhaust and inlet gases respectively. When the

slots on the intake side of both the outer and the inner sleeves

intake pipe, a charge of gas is drawn into the cylinder. After the

explosion has taken place, the sliding motion of the sleeves brings the

other two openings, on the exhaust side, opposite to one another, and

opposite the exhaust pipe, which allows the burnt gas to escape to the

atmosphere through the exhaust manifold.

The sleeves are driven from cranks on the half-time shaft shown at the

side of each cut, through the small connecting rods, which gives them a

reciprocating motion. Like the cam shaft on a poppet valve motor, the

lay shaft runs at half the crank shaft speed, since the engine is of the

four-stroke cycle type. The lower ends of the sleeves, to which the

connecting rods are fastened, are made thicker than the portion within

the cylinder, and are heavily ribbed for strength in the overhang.

The sleeves are of the same composition of cast iron as the cylinder and

are provided with oil grooves cut in their outer surfaces for gas

packing, and the distribution of oil. Leakage between the inner sleeve,

and the cylinder head is prevented by a packing ring, or “junk” ring

that is fastened to the bottom of the inwardly projecting cylinder head.

The junk ring not only prevents the leakage of gas during the explosion,

but it also serves another purpose.

The exhaust ports or slots in the inner sleeve are above the junk ring

during the explosion, in which position they are protected from contact

with the burning gas. The life of valves is greatly increased by this

protection. It will be noted that the entire surface of the sleeves is

in contact with water jacketed surfaces, making perfect lubrication and

smooth working possible. The two spark plugs for the dual ignition

system are shown in the depressed cylinder head.

Complete water jacketing encircles the cylinders, cylinder heads, the

circulation area enclosing the plugs and the gas passages so that a

uniform heat is maintained the entire length of the piston travel.

The half-time shaft, the magneto, and the water pump are driven by a

silent chain from the crank case; this drive being found superior to the

gears commonly used for this class of work. The cranks on the half-time

shaft are made in one integral piece with the shaft.

Although the piston on the Stoddard-Dayton Knight motor has a stroke of

5½ inches, it is scarcely as much as this considered as friction

producing travel, because the inner sleeve in which it rests moves down

in the same direction 1⅛ inches.

This distribution of the working stroke to two surfaces reduces the wear

on the side of the sleeve caused by the angularity or thrust of the main

connecting rod. On the compression stroke, both outer and inner sleeves

go up in the same direction as the piston, the inner sleeve moving the

faster. On the exhaust stroke and suction stroke the sleeves move in a

direction opposite to the direction of the piston, but on these strokes

there is very little work performed by the piston and consequently

little thrust is produced on the sleeves and walls of the cylinder.

It is a valuable feature to have the sleeves descend with the piston on

the working stroke because this is the stroke in which the piston has

the greatest amount of side thrust.

The up and down movement of the sleeves is very little compared with

that of the piston. A stroke of 5½ inches gives a piston speed of 916

feet per minute at a speed of 1,000 revolutions per minute. The stroke

of the sleeves is 1⅛ inches and its speed is but 93.7 feet per minute,

or a little more than one-tenth that of the piston. This fact makes the

problem of lubrication a feasible one, the slow-movement of the sleeves

distributing the oil thoroughly between them as well as between the

outer sleeves and the cylinder walls.

The action of the valves, and their position at different points in the

cycle, is shown in diagrammatic form by Figs. 28–29–30–31–32–33, the

particular event to which each diagram refers being marked at the foot

of the cuts. The direction of the sleeve movement is indicated by the

arrows at the bottom of the sleeves. Particular attention should be paid

to the position of the slots in the sleeves.

The first three diagrams show the position of the inlet slots that

govern the admission of the combustible gas from the carburetor. Fig. 28

shows the slots coming together to form an opening in the inlet port as

the lower edge of the outer sleeve separates from the upper edge of the

inner sleeve. The outer sleeve is now moving rapidly downward while the

inner sleeve is slowly rising, and as their motion is opposite the

opening is quickly formed. Fig. 29 shows the full opening with the slots

in register.

When closing (Fig. 30) the outer sleeve is nearly stationary while the

inner sleeve is rising rapidly. When the inner sleeve port is covered by

the lower edge of the junk ring, the valve opening is closed, the slot

in the outer sleeve remaining opposite the inlet opening.

The exhaust port opens (Fig. 31) when the lower edge of the slot in the

inner sleeve leaves the junk ring in the cylinder head, the sleeve

moving rapidly downward at the moment of opening. To obtain a rapid

opening of the exhaust, the ports are arranged so that the inner sleeve

is just about to reach its maximum speed at the time of opening.

The outer sleeve closes the port (Fig. 33), closure starting when the

upper edge of the outer sleeve coincides with the lower edge of the

cylinder wall port. At this time the outer sleeve is traveling downward

at maximum speed, so that the closing of the exhaust is as rapid as the

opening.

The lubrication of the Knight motor is accomplished by what is known as

the movable dam system, which overcomes the tendency of the motor to

over-lubricate. A movable trough is placed under each connecting rod, in

the crank case, that is connected to the carburetor throttle lever in

such a way that the opening and closing of the throttle raises and

lowers the troughs.

When the throttle is opened, raising the troughs, the points on the ends

of the connecting rods dip deeper into the oil which creates a splashing

of oil on the lower ends of the sliding sleeves. In this way the oil is

fed to the engine in direct proportion to the load and the heat produced

in the cylinder. When the motor is throttled down, the points barely dip

into the oil.

An excess of oil is fed to the troughs by an oil pump, which keeps them

constantly overflowing. The overflow is caught in the pumps located in

the crank case, and returned to the circulation so that it is used over

and over again.

Claims of great efficiency are made for this system, there having been

many tests made showing 750 miles per gallon of oil, while even as high

as 1,200 miles per gallon has been made under favorable conditions.

The oil pump is contained in the crank case, and is of the gear type,

insuring positive action. The pump also acts as a distributer, a slot

being cut in one of the gears which register successively with each of

the six oil leads. In this way it is possible to obtain the full pump

pressure in each lead should they become obstructed in any way.

In the upper half of the crank case are cored passageways through which

the air passes before reaching the carburetor. These passages not only

eliminate the rushing sound of the intake air, but also form an

efficient method of warming the air supplied to the carburetor and

cooling the crank-case. It is possible to furnish warm air after the

engine has been idle for several hours, as the oil in the crank case

remains warm longer than any other part of the engine.

(50) Reeves Slide Sleeve Valve.

A simple and compact form of slide sleeve valve gear has been developed

in England that is of more than passing interest. It permits of a

maximum area for both the inlet and exhaust gases which of course keeps

the velocity and back pressure at a minimum for a given valve lift. The

small lift also insures noiseless operation and a small amount of wear.

The sleeve is balanced at the end of the working stroke. The combustion

chamber is nearly hemispherical in shape which reduces the heat loss to

the walls.

[Illustration:

Fig. 34. Reeves Slide Valve Gear.

]

Referring to the section of the end of cylinder given in the diagram,

(34) A is an open-ended water-jacketed cylinder in which the piston B

works. At the upper end of the cylinder is attached a ring C forming an

extension of the stationary cylindrical head D carrying the sparking

plug. At the lower end of the head D is provided a seating E for the

sliding cylindrical inlet valve F, which takes its bearing around the

circular head. This inlet valve is provided with expanding rings G to

keep it gas-tight. Surrounding the inlet valve F is a second cylindrical

exhaust valve H, which is provided with an angular seating at J. The

outer circumference of the cylindrical exhaust valve H bears against the

walls of the cylinder.

Cast in the cylinder is an annular space K communicating with a passage

L for the admission of the inlet gases. These pass through suitable

ports cut in the sides of the exhaust valve H and the inlet valve F, so

that they are free to pass through the space made when the inlet valve F

is lowered from its seat. A similar type of annular space M is cast in

the cylinder in connection with an opening O for the passage of the

exhaust gas when the cylindrical valve H is raised from its seating at

The cylinder head is not water jacketed as the builder states that the

continual passage of the intake gases keeps it reasonably cool. The

exhaust passages are thoroughly water cooled.

(51) Argyll Single Sleeve Motor.

The Argyll sliding sleeve automobile motor is unique in the fact that

only one sleeve is used to control both the inlet and exhaust gases

instead of the two sleeves commonly used on the Knight motor. This

sleeve, instead of having either a purely vertical or horizontal motion,

has a peculiar combination of the two, that is to say, it moves a

certain amount in rotation within the cylinder, and an equal amount

vertically, the combined motion constituting an ellipse. The external

appearance of the engine is shown by Fig. 35, which will give an idea of

the general arrangement of the cylinders, ports and piping.

In Fig. 36, is shown the successive movements and events determined by

the sleeve, and the method of opening and closing the inlet and exhaust

ports by the elliptical movement of the sleeve. The shaded ports are one

of the inlet and one of the outlet ports, respectively, which are cast

in the cylinder wall, and are afterwards machined true. The dotted port,

which changes its position in each diagram, is one of the ports in the

moving sleeve, its position in each of the figures is marked by the

event that is occurring in the cylinder at that time.

In diagram 1, the shaded port to the right is the exhaust port, and the

shaded port to the left, the inlet, this relative arrangement being

true, of course, in each of the succeeding diagrams. It will be noted,

that in the position shown, in the exhaust stroke (beginning of stroke),

the sleeve port has just started on its downward stroke, moving also a

trifle to the right as it progresses. Its progress to the right may be

more clearly seen by consulting diagram 2, for the movement.

By consulting the other five figures it will be seen that the dotted

port, in its relation to the shaded ports, first moves out to the right,

and then reverses, moving to the left, and this combined with the up and

down movement constitutes an elliptical path. In diagram 6 the exhaust

is closed, and the inlet port has just begun to open, the dotted port

now starting to move out to the left, and to rise.

[Illustration:

Fig. 35. Elevation of Argyll Single Sleeve Motor from The Motor,

London.

]

In diagram 10, the inlet is nearly closed, the sleeve port passing away

from the cylinder ports to the water jacketed portion of the cylinder

above.

[Illustration:

Fig. 36. Valve Motion Diagram of Argyll Motor Showing the Valve

Positions at Different Parts of the Working Stroke.

]

This series of diagrams shows the operation of the duplicated port of

the sleeve (which port is the one shown dotted) in relation with one of

the inlet ports and one of the exhaust ports in the cylinder wall, the

latter ports being marked respectively I and E. The elliptical movement

referred to in the text can be traced by following the different

positions of the dotted port in the sleeve. In the top row of diagrams

it is seen to come downwards and also to move over to the left, whilst

in the lower set it rises—bearing still to the left—until, after Fig.

10, it goes higher up for the compression and explosion strokes, during

which it bears over to the right and comes down again ready to commence

once more the cycle, as in Fig. 1. The other ports in the cylinder wall

are the same as those shown, and the other ports in the sleeve are akin

in shape to half of the dotted port, but they are without the little

tongue cut in the base of this double purpose port. This little tongue

in the duplicated port is designed to give as much lead to the exhaust

opening as possible, without interfering with the correct timing of the

inlet port. The way in which it just misses interfering with the closing

of the inlet port is seen in Fig. 10. We are indebted to “The Motor” for

these cuts.

(53) Sturtevant Aeronautical Motor.

The cylinders of the Sturtevant aeronautical motor are of the “L” type

and are cast separately with the cylinder barrel and water jacket in one

integral casting. A special iron is used for these castings that has an

ultimate tensile strength of 40,000 pounds per square inch. The valves

which are easily accessible through valve covers, are operated directly

from the cam shaft without valve rockers. A hollow cam shaft is used

with integral cams to insure a maximum of strength with a minimum of

weight, and bearings are placed between each set of cams. A bronze gear

fitted on the cam shaft meshes with a gear on the crank shaft without

intermediate idlers.

[Illustration:

Fig. 41. Six Cylinder Sturtevant Aero Motor.

]

Like the cam shaft, the crank is bored out from end to end with a

propeller flange applied on a taper at one end of the shaft. A bearing

is provided between each throw with an additional thrust bearing at the

forward end of the shaft which may be arranged to take either the thrust

or the pull of the propeller. Lubricating oil is applied to all the

bearings under a pressure of twenty pounds per square inch, this

pressure being maintained by a gear pump attached directly to the end of

the cam shaft. The oil is transferred from the pump to the bearings

through passages cast in the base, no piping being used. Oil enters the

hollow crank shaft at the main bearings and is conducted through the

arms to the connecting rod bearings. The oil flying from the crank shaft

falls into the oil sump at the bottom of the case where it is cooled

before being used again. A second gear pump in tandem with the first

takes the oil from the sump and forces it through a filter into the

tank.

[Illustration:

Fig. 43. Crank Shaft of Sturtevant Motor.

]

[Illustration:

Fig. 42. Crank Case of Sturtevant Motor.

]

This system enables the use of a more efficient filter than with the

suction type and eliminates any danger of its becoming clogged and

stopping the oil supply, since, in the event of such an occurrence the

pump would furnish sufficient pressure to burst the filter. However, the

filter is particularly accessible and may be instantly removed for

cleaning without disturbing the oil. The tank regularly fitted to the

motor holds sufficient oil for three hours’ use. If the engine is

required to operate for a longer time without opportunity for

replenishing the oil supply, a larger tank can be used. As no oil is

allowed to accumulate in the base with this system of lubrication, the

motor can be operated continuously at an angle.

Water circulation is maintained by a centrifugal pump of large capacity,

the impeller of which is mounted directly on an extension of the crank

shaft, eliminating the usual bearings and its grease cup.

The ignition is provided by a high-tension Mea magneto, its special

construction permitting the motor to be started under a retarded spark

avoiding the danger of back kick from the propeller.

The cylinder and all exposed parts are rendered absolutely weather-proof

by means of a heavy coat of nickel plating.

(54) The Rotating Cylinder Motor.

While it is the common belief that the rotary cylinder gasoline motor is

of French origin it may safely be said that this type of motor was in

actual use in America for several years before it even reached the

experimental stage in Europe. The Adams-Farwell Company of Dubuque,

Iowa, were driving automobiles successfully with a rotary cylinder motor

before Orville Wright flew at Fort Meyer, Va. Although the original

Farwell motor more than proved its right to existence by faithful

service under the most exacting conditions, the motor never received the

consideration that it deserved, probably because of its great divergence

from what is known as “accepted practice.”

In Europe no such prejudice existed, and consequently the type made

rapid strides, although, to the writer’s belief, the European model is

inferior in many ways to the original American type. The fact that this

type of motor holds practically all of the world’s aviation records

speaks for its practicability in spite of its unusual construction.

With the rotary motor, the cylinders and crank case revolve about a

stationary crank shaft, the latter part not only serving as a point of

reaction of the cylinders but as a support and intake pipe as well.

Since the crank throw remains stationary, the cylinders and pistons

revolve about two different centers, the cylinders revolving about the

crank case and the pistons and connecting rods about the crank pin.

Since the pistons, cylinders, and connecting rods must necessarily

revolve together, as one unit, there is absolutely no reciprocating

motion in regard to the crank shaft except for a very slight movement

due to the difference in angularity of the connecting rods. The motion

of all the parts is strictly rotary in every sense, except for the

relation of the pistons to the cylinders, and the motion is as

continuous as in a turbine. This insures freedom from vibration. As the

cylinders and crank case have considerable inertia there is no need of

the added weight of a fly-wheel. The movement of the piston in the

cylinder bore is brought about by the difference in the centers about

which these parts revolve. This gives cylinder displacement without the

reversal of stresses or shock or jar.

Because of the revolving cylinders, the mixture is supplied to the crank

case through a hollow shaft, the gas being drawn into the cylinder on

the suction stroke through an inlet valve placed in the head of the

piston. As a rule, the exhaust is direct to the air through the exhaust

valves and without manifolds or mufflers. The motion of the cylinders

through the air multiplies the efficiency of the radiating Fins.

(55) The Gyro Rotary Motor.

In the Gyro motor, made by the Gyro Motor Company of Washington, D. C.,

are embodied all of the principles of the typical revolving motor, but

with extensive improvements in the design and in the details. It weighs

3¼ pounds per horse-power, complete. This light weight is due to the

design of the motor and to the use of alloy steels, and is attained

without sacrificing strength or durability.

Each cylinder is machined out of a heavy 3½ per cent tubular nickle

steel forging that weighs nearly 40 pounds. After the metal is removed

and the cylinder worked down to size, the shell weighs but 6½ pounds.

The radiating ribs on the outside of the cylinder are machined out of

the solid bar, and are arranged in helicoid or screw-like formation

around the cylinder barrel. This adds to the strength of the cylinder

and also aids in the circulation of the air. The comparative thickness

of the cylinder wall may be seen from Fig. 44. The stiffening effect of

the radiating ribs will also be noted. The crank case to which the

cylinders are fastened is of vanadium steel, and is divided into two

parts. In addition to supporting the cylinders, the crank case also

serves as a mixing chamber for the gasoline and air. By removing the

bolts seen between each cylinder, the entire working mechanism can be

laid bare for inspection. The exterior of the case carries the exhaust

valve mechanism and the ignition distributer. The crank shaft is a

nickel steel forging with an elastic limit of 110,000 pounds. It is

bored hollow throughout its length and serves as an intake manifold by

conveying the mixture from the carbureter, attached to its outer end, to

the crank case.

[Illustration:

Fig. 45. Section Through Rotary Gyro Motor.

]

The intake valves in the heads of the piston are mechanically operated

by a specially patented movement which consists of two parts, a

counter-balancing member, and an operating member. The counter balance

balances the valve against the disturbing influence of the centrifugal

force, while the operating member, which is fastened to the connecting

rod, controls the opening or closing of the valve by the angular

position of the connecting rod. This valve action insures a full opening

of the valve and a full charge during practically all of the suction

stroke.

There are two separate paths provided for the exhaust gases, one being

through the auxiliary exhaust ports at the end of the stroke, and the

other path through the exhaust valve located in the cylinder head. The

auxiliary ports may be seen in the cross-section directly below the

piston head in cylinders 4 and 5. The auxiliary ports are uncovered by

the piston at the inner end of the working stroke, and it is at this

point that the greater percentage of the exhaust leaves the cylinder.

These ports or holes are formed on a projecting annular ring in which

enough material is provided to make up for the strength lost by boring

the ports. As these ports are, in the majority of cases, bored at an

acute angle with the center line of the cylinder, it is impossible for

the cylinder oil to escape.

All exhaust valves are operated by levers and push rods connected to a

cam mechanism on the outside of the crank case. A single cam ring

operates all of the valves except where a step-by-step compression is

desired. The exhaust mechanism is provided with a simple device by which

the closing of the exhaust valve may be delayed through any portion of

the exhaust stroke, thus reducing the compression and adding to the

facility of cranking. The motor is started with the compression entirely

released in which condition it can be spun about its shaft with ease.

After giving the motor its initial spin, the compression and spark are

thrown in and the engine begins its normal operation. The compression

release lever may be used for starting or slow running and in cutting

off the power regardless of the ignition advance or retard.

One connecting rod, called the “master” rod, is an integral part of the

spider that contains the ball bearings of the crank pin, thus

controlling the angular relation between the connecting rods and

cylinders. The remaining six rods are, of course, articulated on the

spider by pins so that the rods may move in regard to the spider when in

different parts of the stroke. The shell of the pistons is of a fine

grade of iron, very thin and elastic, so that it may conform readily to

the outline of the cylinder bore. The head of the piston consists

principally of the intake valve cage, the cage carrying the piston pin

as well as the valve.

Practical Hand Book of Gas, Oil and Steam Engines Stationary, Marine, Traction; Gas Burners, Oil Burners, Etc.; Farm, Traction, Automobile, Locomotive; A simple, practical and comprehensive book on the construction, operation and repair of all kinds of engines. Dealing with the various parts in detail and the various types of engines and also the use of different kinds of fuel. · 第 16 / 20 章

In the sliding sleeve type of four stroke cycle motor, the poppet or