Oil is supplied by a positive pump that _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.

proportion to the load on the engine. Both the oil and the gasoline

mixture enter the crank case through the hollow crank shaft and mingle

in the form of a vapor. This oil mist reaches every moving part and

results in perfect lubrication. The pistons are provided with oil

shields which carry the oil directly to the cylinder walls and prevent

the loss of oil through the exhaust valve.

Ignition is performed by a high tension magneto through a distributer

which directs the current to the proper cylinder. As in all rotary

engines, the Gyro has an uneven number of cylinders (3, 5, and 7) in

order that the cylinders receive firing impulses through equal angles of

rotation. An even distribution of firing is impossible with an even

number of cylinders, as two adjacent cylinders out of six alternately

fire together and then 180° apart. This produces a very jerky turning

movement, and is productive of much vibration. In the seven cylinder

motor the magneto is driven by gears having a ratio of 4 to 7, and the

high tension current is distributed to the cylinders by 7 brushes, the

leads from the brushes being taken direct to the spark plugs.

(56) Gnome Rotary Motor.

The Gnome was the first rotary aviation motor built in Europe and is

still one of the most capable flight motors abroad as its many victories

and records prove. It is built in four sizes, 50, 70, 100, and 140

horse-power, the 50 and 70 horse-power motors having 7 cylinders, and

the 100 and 140 horsepower, having 14 cylinders, which consist of two

rows of 7 cylinders per row. The cylinders of all sizes rotate about a

stationary crank shaft while the pistons rotate in a circle, the center

of which is the crank pin. Vibration is practically eliminated at high

speed as the pistons do not reciprocate in the ordinary sense of the

word, but simply revolve in a circle, the reciprocating relation between

the cylinders and pistons being obtained by the difference in the

centers of the two revolving systems. The cooling effect of the

radiating ribs is greatly increased by the air circulation set up by the

rotation of the cylinders. This method of cooling introduces a great

loss of power due to the blower action of the cooling ribs, this loss

often amounting to 15 per cent of the output of the engine.

[Illustration:

Fig. 50. Cross-Section Through the Seven Cylinder Rotary Gnome Motor,

Showing the Crank Shaft Arrangement and Valves.

]

The crank shaft is stationary and acts as a support for the engine, one

end being fastened into a supporting spider which forms a part of the

aeroplane frame. The crank shaft is hollow and also serves to conduct

the mixture from the carburetor fastened at its outer end to the

crank-case of the motor. Only one crank throw is provided on the seven

cylinder engine as the cylinders are all arranged in one plane which

passes through the center of the crank throw. In the fourteen cylinder

engine where the cylinders are in two rows, there are two crank throws,

one for each row of cylinders.

The seven cylinders are arranged radially, as will be seen in Fig. 50,

each being spaced at an equal distance from the crank shaft and at equal

angles with one another, the arrangement in general being similar to

that of the “Gyro” motor shown in the preceding section. All cylinders

are turned out of solid forged steel bars, the cylinder walls being only

1.2 millimeters thick after the machining operation. This results in the

strongest and lightest cylinder possible to build, as all superfluous

material is removed and the chances of defects in the material are

reduced to a minimum as the character of the metal is revealed by the

extended machining operations.

[Illustration:

Fig. 51. Firing Diagram of Seven Cylinder Rotary Motor. On Starting at

Cylinder No. 1, and Following the Zig-Zag Line in the Direction of

the Arrows, it Will be Seen that Ignition Occurs at Every other

Cylinder at even Intervals Through Two Revolutions, Ending at

Cylinder No. 1.

]

As the motor operates on the four stroke cycle system, an odd number of

cylinders is chosen in order that the firing may be carried out through

equal angles in the revolution to obtain a uniform turning movement.

Since a four stroke motor must complete two revolutions before all of

the cylinders have fired, or completed their routine of events, it is

evident that the number of cylinders must be odd in order to bring the

last cylinder into firing position in the last revolution. When seven

cylinders are used, the cylinder are fired alternately as they pass a

given fixed point, that is, one cylinder is fired, the next skipped, the

third fired, and the fourth skipped, and so on around the circle, so

that the firing order in terms of the cylinder numbers is 1, 3, 5, 7, 2,

4, 6. The cylinders fired in the first revolution in order are 1, 3, 5,

7, and in the second revolution, 7, 2, 4, 6, the cylinder 7 being common

to both revolutions. The cylinders are numbered according to their

position on the engine, and =NOT= according to the firing sequence. See

Fig. 51.

[Illustration:

Fig. 52. Firing Diagram of Six Cylinder Rotary Motor. On Following the

Zig-Zag Line it Will be Seen that All of the Cylinders Are Not Fired

at Equal Intervals. In Some Cases Two Adjacent Cylinders Fire in

Sequence, and in Others Two or Three Spaces are Jumped.

]

With a six cylinder engine it is possible to fire the cylinders in two

ways, the first being in direct rotation; 1, 2, 3, 4, 5, 6 thus

obtaining, six impulses in the first revolution, and none in the second.

The second method is to fire them alternately, 1, 3, 5, 2, 4, 6, in

which case the engine will have turned through equal angles between

impulses 1 and 3, and 3 and 5, but through a greater angle between 5 and

2, and even again between 2 and 4, and 4 and 6. See Fig. 52.

Mixture is drawn into the cylinder by the suction of the piston through

an inlet valve in the piston head, in practically the same way as in the

“Gyro” motor, but unlike the latter motor, the valve is lifted by the

suction (automatic valve) and not by the mechanical actuation of the

connecting rod. The inlet valve is balanced against the effects of

centrifugal force by a small counter-weight in the piston head, and the

valve is held normally on its seat by a flat spring acting on the valve

stem. The gases are brought into the crank case from the carburetor

through the hollow crank-shaft as described elsewhere. See Fig. 53.

[Illustration:

Fig. 53. Longitudinal Section Through Gnome Rotary Motor.

]

All exhaust valves are located in the cylinder head and are actuated by

long push rods that are moved by individual cams in an extension of the

crank case. The exhaust valves are counter-balanced against centrifugal

force and are retained on their seats by a flat spring. The counter

weights do not entirely overcome the effects of the centrifugal force

but allow a slight excess to exist which will permit the engine to run

with a broken spring. All of the exhaust gases escape directly to the

atmosphere without piping or mufflers.

Owing to the fact that the advancing or leading face of the cylinder is

cooler than the trailing face, the cylinder bore is thrown out of line

by the difference in expansion between the two sides. Because of this

distortion of the bore, a special form of piston ring is used, which, by

its flexibility, adapts itself to variations in the bore. These rings

are of brass and are shaped like the pump leathers of a water pump so

that the pressure of the explosion acting on the inside of the ring

tends to force the thin shell against the cylinder. In spite of this

precaution, the compression pressure is very low at the best, in the

most of cases not over 45 pounds per square inch. The exhaust valve

screws into the end of the cylinder and may be removed, complete with

its seat, for the frequent regrinding necessary to efficient operation.

After the cylinders are ground with the greatest care and accuracy, the

finishing is carried still further by wearing-in the cylinder with an

actual piston carrying an “obturateur” or piston ring.

[Illustration:

Fig. 54. Gnome Motor on Testing Stand. From Scientific American.

]

The bushing into which the spark plug screws is not integral with the

cylinder as in a cast construction, but is welded into the side of the

cylinder head by means of the autogenous process. It is also evident

that this construction enables the inlet valves to be easily removed,

since these screw into the piston head. Both inlet and exhaust valves in

the Gnome engine are removed with the greatest ease, special socket

wrenches being supplied for the purpose. The castor oil, which is used

as a lubricant, and the gasoline, are fed by a positive acting piston

pump to the hollow crank shaft. The lubricant and fuel then pass through

the automatic inlet valve in the head of the cylinder.

[Illustration:

Fig. 55. Gnome Motor Running On Test Stand. From Scientific American.

]

The spark produced by the high tension magneto is led to the proper

cylinder through a brush that presses on a revolving ring of insulating

material in which is imbedded 7 metallic segments, one of the segments

being connected to a corresponding cylinder. As the distributor ring

revolves the segments come into contact with the brush in the proper

order. The magneto is stationary and is supported by a bracket in an

inverted position. A pinion on the magneto shaft meshes with a large

gear mounted on the revolving crank case so that the armature of the

magneto always bears a positive relation to the piston position. As the

engine requires seven sparks for every two revolutions, or 3½ sparks per

revolution it is evident that the magneto must turn 1.75 times as fast

as the engine, if the magneto is of the ordinary type that generates two

sparks per revolution. In other words the magneto speed is to the engine

speed as 7 is to 4.

[Illustration:

The “Indian” Rotary Aero Motor.

]

The arrangement of connecting rods is interesting, the big end of one

rod being formed into a cage for the reception of the crank-pin ball

race. The outer circumference of the cage carries the pins to which the

other six connecting rods are fastened. It is necessary that one rod be

integral with the cage to prevent its rotation in regard to the

cylinders. Annular ball bearings are used on both the main bearings, for

the thrust bearing to take the thrust of the propeller, and on the large

end of the master connecting rod. The large ends of the auxiliary

connecting rods and the small ends of all the rods have plain bearings.

CHAPTER VI

TWO STROKE CYCLE ENGINES

(30) The Junker Two Stroke Cycle Engine.

The Junker two stroke cycle engine stands unique among the large

stationary units not only in the principle of its working cycle but in

its construction as well, and while it may be considered freakish when

compared to standard practice it has proved its value in many European

installations. The combustion occurs in the center of an open ended

cylinder between two pistons that are forced in opposite directions by

the expansion of the gas, and as there is a single acting piston in each

end of the cylinder at the end of the stroke, there is no need of

stuffing boxes, cylinder heads or valves.

It is apparent that by moving the pistons in opposite directions, the

effective piston velocity is twice that of the actual velocity of either

of the pistons, and that it is therefore possible to gain a high heat

efficiency at high piston velocities with a low rate of rotation. The

double pistons increase the scavenging effects, reduce the losses to the

cooling water and increase the efficiency at light loads. A marked

reduction in weight over the four stroke cycle engine is made possible

because of the absence of valves and valve gear.

This engine is of the injected fuel type that is the fuel is sprayed

into the combustion chamber after the completion of the compression

stroke in a manner similar to the Diesel engine. By prolonging the

injection of fuel after the piston has started on the outward working

stroke it is possible to maintain the maximum pressure due to the

combustion for a considerable period. This gives an indicator card that

is very similar to that of a steam engine as the flat top of the

Junker’s card due to the continued combustion and pressure corresponds

to the admission line of the steam engine. As ignition is caused by the

high temperature of the compression, almost any low grade oil may be

used even down asphaltum oils and coal tar.

[Illustration:

Fig. 8. The Junker Two Stroke Cycle Engine.

]

In Fig. 8 five piston positions corresponding to five events are shown

by the diagrams a, b, c, d, e. From the diagrams one may also get an

idea of the arrangement of the principal parts of the engine and their

relation to one another. P and P2 are the two pistons, C the open ended

cylinder, G the connecting rod of the inner piston P, H-H the two

connecting rods of the piston P2, I-I the side rods of the piston P2,

and V is the three throw crank shaft which is acted on by the three

connecting rods H-H-G. The piston P2 is connected to the side rods

through the yoke Y. It will be noted that the crank throws controlling

the piston P2 are 180° from the crank connected to piston P, which

causes the pistons to move in opposite directions.

With the pistons together at the inner dead center, the space between

them is filled with highly compressed air from the previous combustion

stroke. At this point the fuel is injected into the highly heated air,

and the expansion of the charge begins, the combustion proceeding under

constant pressure during the first part of the stroke, or during that

part of the stroke in which the fuel is admitted to the cylinder. When

the supply of fuel is cut off the working stroke continues by the

increase of volume, or expansion of the gas, the gases being reduced to

nearly atmospheric pressure at the end of the stroke with the pistons at

the position shown by diagram (b). At this point the piston P is just

opening the edge of the exhaust port M, allowing the products of

combustion to escape to the atmosphere through the annular exhaust

passage that surrounds the port M.

As the pistons continue to move outwards the gases continue to issue

from the exhaust port at practically atmospheric pressure until the

position shown by diagram (c) is reached by piston P2. At this point P2

is just opening the inlet port N allowing fresh air to enter the

cylinder for the purpose of scavenging the engine. The passage of the

air through the intake port N and out through the exhaust port M

continues until the pistons pass the outer dead center, shown by diagram

(d), and begin to come back on the return stroke. In diagram (e) the

pistons have traveled far enough to close both ports, and as the space

between them is filled with pure air from that furnished by the port N,

the pistons will continue to move toward one another on the compression

stroke. When they have reached the end of their travel as shown by

diagram A, the fuel is injected into the cylinder and combustion occurs

due to the temperature of the high compression temperature.

This is the complete cycle of events made in two strokes, and it will be

noted that the cycle has been accomplished without the use of valves.

The compressed air for scavenging the cylinder is provided by air pumps

that are driven from the connecting rods by a link motion. One low

pressure pump for the scavenging and one high pressure pump for spraying

the fuel into the cylinder against compression are provided. As the

inside of the piston is always exposed to the atmosphere through the

open ends of the cylinder and is never exposed to the heat of

combustion, perfect cooling is secured, and as a matter of course,

perfect lubrication.

In the two cylinder engine in which four pistons are used, the cylinders

are arranged in tandem with the two adjacent pistons, and the two outer

pistons connected respectively. In fact the second cylinder pistons are

duplicates of those just shown and are connected to the linkage in such

a manner as to have the corresponding pistons in one cylinder act with

the corresponding pistons in the second.

(34) Koerting Two Stroke Cycle Engine.

One of the most prominent of the two stroke cycle scavenging engines

built for heavy stationary service is the Koerting engine. Because of

its peculiar scavenging arrangement, and as it is of the double acting

type, it will serve to illustrate the cycle of that class of engine

equipped with independent air pumps. Several of these engines are in use

in Europe that have an output of over 4,000 horse-power, the general

arrangement of which is the same as shown in the accompanying diagram

Fig. F-11.

[Illustration:

Fig. F-11. Koerting Two Stroke Cycle Engine with Scavenging and

Charging Cylinders.

]

Since the engine is double acting, two similar combustion chambers are

provided at each end of the piston as shown by C and C_{1}, and as each

of the chambers gives one impulse per revolution because of the two

stroke cycle, the single cylinder shown in the figure delivers two

impulses per revolution to the crank-shaft. In order to have one exhaust

port serve for both combustion chambers, the annular port E is placed in

the center of the cylinder so that it is alternately opened to C and

then C_{1} as the piston travels to and fro, the port being covered by

the piston at intermediate points in its travel. As the piston must

cover the port for a considerable portion of the stroke, it is made very

long, nearly as long as the stroke. The piston rod R that connects the

piston with the crank passes through the cylinder head of chamber C_{1},

surrounded by a gas tight packing that prevents the leakage of the

charge from C_{1}.

Unlike the ordinary type of two stroke cycle engine, the two combustion

chambers are provided with mechanically operated inlet valves,

V-V_{1}-V_{2}-V_{3} that are opened at definite points in the stroke by

the lay shaft X which is driven from the crank shaft. As the exhaust

port E serves all of the functions of an exhaust valve, there are no

valves provided at this point. Exhaust pipes connected to E carry the

burnt gases to the atmosphere.

Two auxiliary air pumps of the double acting type are provided, shown at

A and A_{2}, one pumping gas and the other air. They are driven from the

crank-shaft through the connecting rod Y, and are proportioned so that

together they force a mixture of the correct proportion for complete

combustion into the working cylinder at a pressure of about ten pounds

per square inch. Air and gas are compressed on one side of each pump

piston in the spaces B and B_{2}, and the air and gas are drawn in on

the other side as at H and H_{2}. The connections from the compressor

cylinders to the working cylinder are arranged so that the two crank

ends of the compressor cylinders discharge into the crank end of the

working cylinder, and the front ends of the compressors discharge into

the front end of the working cylinder, the exact moment of discharge

being controlled by the inlet valves V-V_{1}-V_{2}-V_{3}. The pumps are

arranged so that only pure air is admitted at first in order to force

the products of combustion through the exhaust port so that they will

not contaminate the following mixture of air and gas. The inlet valve

opens immediately after the piston of the working cylinder uncovers the

port E and reduces the pressure of the burnt gases to that of the

atmosphere.

By the action of the admission control, the scavenging air first

admitted, is prevented from mixing with the residual gas from the

previous explosion, and in the same way the device prevents the loss of

fuel through the exhaust ports, thus overcoming the principal objections

of the simple two stroke types described earlier in this chapter. The

compressor cylinders provide only enough air and mixture for one stroke

and no reservoir is provided for a surplus of air or mixture.

As the piston moves forward, on the compression stroke and covers the

exhaust port, the inlet valves also close, and the compressor pistons

arrive at the end of their stroke so that no more air or mixture is

delivered to the inlet valves. At the end of the compression stroke

ignition occurs and the expansion or working stroke begins. The piston

again moves to the right on the working stroke until the front edge

uncovers the port E where the exhaust gases escape to the atmosphere.

The valve gear on the gas compressing cylinder is arranged so that no

gas is delivered to the inlet valves of the working cylinder until the

air cylinder has provided sufficient air to insure perfect scavenging of

the products of combustion, this preventing the fuel from becoming

contaminated with the burnt gas. Speed regulation for varying loads is

effected by shifting the valve gear of the gas pump so that the gas is

delivered at an earlier or later period in the stroke of the working

piston, thus causing a variation in the quantity of gas delivered to the

working cylinder. This is controlled by the governor directly on the

valve gear of the pump or upon a by-pass in the pump cylinder or both.

The by-pass, when open returns all of the gas in the passage leading to

the inlet valve, that is beyond a certain pressure to the cylinder, so

that the gas is delivered to the cylinder at a constant pressure, and

therefore in proportion to the load and point of cut off.

This method of governing produces a mixture that varies in richness with

the different loads that are carried by the engine, but as the air

enters the cylinder first and is prevented from mixing to any extent

with the gas by the shape of the cylinder heads, the igniting value of

the mixture is not disturbed particularly as the rich gas remains in the

cylinder heads and in contact with the igniters.

Like all large engines, the Koerting is started by compressed air taken

from a reservoir. A special starting valve is provided for each end of

the cylinder which is operated from the cam shaft by means of an

eccentric. The air valves may be thrown in or out of gear by a clutch.

(57) Two Stroke Cycle Rail Motor Cars.

A unique application of the two stroke cycle motor will be seen in Fig.

56 which shows a Fairbanks-Morse two stroke cycle motor direct connected

to the driving wheel of a railway motor car. The three cylinders are

mounted between the driving wheel with the ends of the axle terminating

in the crank cases of the motors. Access to the bearings is had through

a cover on the crank-case. The simplicity of this motor and its freedom

from valves, cams, springs, gears, and other trouble causing parts makes

it particularly adapted for the service that it performs in the hands of

unskilled track laborers. As there is no water to freeze or leak, and as

the lubricant is mixed with gasoline, the car needs very little more

attention than the old type hand car.

The car is started by opening the gasoline supply cock, closing the

ignition switch, and pushing the car along the track until the first

explosion occurs. The speed is controlled in the usual manner by means

of the spark advance and throttle. As the motor is of the two stroke

cycle type, it may be reversed by simply changing the position of the

timer without the use of the gears. The speed is the same in either

direction. By the use of three cylinders, three impulses are obtained

per revolution which gives a distribution of power equal to that of the

ordinary six cylinder, four stroke cycle automobile motor.

[Illustration:

Fig. 56. Two Stroke Cycle Fairbanks Motor for Driving Railway Section

Cars.

]

For larger cars built for carrying large gangs of men, a three cylinder

motor is used which drives through a clutch and gears, similar to that

used on automobiles. It is located near the center of the axle and is

supported on a frame that is independent of the car proper. This motor

unit is easily removed from the car for inspection with all of the parts

intact. A universal coupling is provided on the motor shaft to prevent

strains due to changes in the alignment from being thrown into the

motor. The motor of this car is started with a crank, and may be left

standing with the motor running. As with the two cylinder car, the

engine is reversible, and is lubricated by mixing the lubricating oil

with the gasoline.

(58) Rotating Cylinder Two Stroke Cycle Motor.

An unusual type of two stroke cycle engine is that designed by M. Farcot

for aeronautic work. It is of the rotating cylinder type in which the

cylinders rotate about a stationary crankshaft, and unlike all previous

two stroke motors, whether of the revolving or stationary cylinder type,

no initial compression is performed either in the crank-case or

otherwise.

[Illustration:

Fig. 63. Farcot Rotary Two Stroke Motor.

]

Undoubtedly the two-cycle rotating multi-cylinder engine has a future

when some of the particularly difficult designing problems involved in

its production have been successfully tackled. Crank case compression

has had its devotees, but so far it has entailed the use of a low

compression, owing largely to the difficulties involved in lubricating

the bearings and maintaining gas-tight joints, besides other defects.

Some of these barriers appear to have been surmounted in this design.

Fig. 63 of the accompanying drawings is a sectional side elevation of

the engine, which, it will be seen, is similar in general disposition to

the usual arrangement of the rotating cylinder type. In this particular

case, however, the short end A of the stationary crankshaft is reduced

in diameter at B, and on this part are mounted ball bearings C carrying

the circular casing of a rotating centrifugal blower D. To the inner end

of the hub of this blower is attached a gear wheel E, the teeth of which

mesh with small intermediate pinions carried on a spider F attached to

the crankshaft. These pinions are in turn driven by an internally

toothed ring G attached to the hub of the crank case H. Thus the blower

D is driven in the opposite direction to the crank-case and at a higher

speed. In the interior of the blower casing radial blades K are

provided.

[Illustration:

Fig. 64. Farcot Fan Plates.

]

A hollow annular casing L is bolted to the cylinders, and communicates

with their interiors by means of inlet ports M covered and uncovered by

the pistons.

The blower casing D has on either side circumferentially flanged rings

N, which are a running fit in circular register slots provided in the

annular casing L and its cover plate P, in order to provide a gas-tight

joint between the opposite revolving casings D and L. Fan blades Q are

also provided in the casing L to accelerate still further the incoming

gas. The arrangement of the two sets of blades is made clear in the

sectional sketch (Fig. 64). It will be realized that by means of this

compound blower device a considerable pressure can be attained.

The crankshaft is drilled to provide a feed for the gasoline, which is

atomized by a device R in the large central opening of the blower casing

D by means of pressure fed from the annular casing L through suitable

leads S.

As each piston nears the bottom of its stroke, exhaust ports T, provided

with expansion cones for the purpose of increasing the velocity of the

exhaust gases, are opened. The inlet port M is then uncovered, and the

compressed charge rushes into the combustion chamber.

The general design of the engine is made plain by Fig. 63, but there is

one other point to which reference should be made, and that is the

provision of rings V, one on either side of the cylinders, to enhance

the strength of the construction.

Although the difficulty of compression appears to have been cleverly

tackled in this invention, the possibility of the compressed mixture in

the inlet casing and blower becoming ignited at the moment of admission

by a residue of exhaust gas in the combustion chamber still exists.

However, the effect of such a backfire should not prove quite so serious

as in some designs. Apart from other considerations, owing to the large

area of the blower intake, such an occurrence should merely have a more

or less elastic braking effect.

(60) Gnome Radial Two Stroke Motor.

The builders of the famous Gnome four stroke cycle rotary motor, Sequin

Frères, have recently developed a radial two stroke cycle motor that

bids fair to supplant their original type. Referring to the diagrammatic

cross-sections which show only a single cylinder unit, a very long

tubular piston will be seen that is divided into two independent

chambers, A and B. Both chambers are placed in communication with the

outside space, C and D.

The upper end of the piston is continued above the top division head of

the chamber A, and the extension is provided with the slot F. Near the

center of the piston, the walls of the piston are run out into a flat

circular plate or trunk piston E, which is the actual piston head that

receives the force of the explosion. The piston E reciprocates in the

large cylinder H, which is reduced at its upper end to the diameter of

the main piston barrel, for which it affords a sliding support, or

guide, and also serves to aid the exhaust port closure. The lower end of

the cylinder H is enlarged in diameter as shown by K so that a clear

annular space is left between the cylinder walls and the piston head E,

when the latter is at the bottom of the stroke. The cylinder diameter is

then reduced to the diameter of the main piston barrel.

The motor operates as follows:

Suppose the piston to be ascending (Fig. 1), compressing the mixture

above the piston head in the cylinder E, and at the same time the volume

of the space M, below E, is being increased until the piston reaches the

position shown in Fig. 2.

[Illustration:

Fig. 65. Gnome Rotary Two Stroke Motor Diagram. Diagrams 1 and 2.

]

Referring to Fig. 1; the interior chamber A of the piston is in direct

communication through the holes C with the space M, consequently as the

piston goes up, a partial vacuum will be formed in these two chambers.

When the piston reaches the top of its stroke as shown in Fig. 2, the

holes D in the lower end B of the piston are uncovered as they rise into

the increased diameter of the cylinder, and therefore the mixture is

sucked in from the crank case until the chambers A and M are filled to

atmospheric pressure.

The spark now occurs at the plug S, and the explosion takes place,

driving the piston downwards as shown by Fig. 3, just before the exhaust

takes place. The volume of the chamber M has now been decreased with the

result that the mixture will have been compressed into the chamber A.

In Fig. 4, the piston has now reached the bottom of the stroke, and the

ports F have opened as the slots carry below the upper end of the

cylinder where the bore is increased. At the same time, as the piston

plate E passes the bottom of the cylinder H into the enlarged diameter

K, the compressed mixture in A and M rushes through the annular space

opened around E into the combustion chamber and drives out the residual

burned gases which still remain after the explosion. On starting the

second revolution the piston rises and the cycle repeats as shown by

Fig. 1.

[Illustration:

Gnome Rotary, Diagrams 3 and 4.

]

This engine may be built with any number of the cylinder units

described, preferably with an uneven number, as in the case of the Gnome

radial four stroke cycle, and with twice the number of impulses of the

four stroke type a very uniform turning movement should be had.

[Illustration:

Fig. 64-b. Roberts Two Stroke Aero Motor Using a Rotating Tubular

Valve that Controls the Mixture from the Carburetor so that it

Enters Only One Crank Case at a Time. This Gives Each Cylinder an

Equal Charge of Gas.

]

[Illustration:

Fig. 64-c. Roberts Distributor Valve. The Ports Are Cut in the Valve

so that Only One Crank Case is in Communication with the Carburetor

at Any One Time. The Central Hole Connects with the Carburetor.

]

Since the valves are the parts that give the most trouble in the

four-stroke cycle Gnome, this motor should be better adapted for

aviation than the original type of Gnome.

(62) Variable Speed Two Stroke Motor.

A variable speed two stroke cycle motor is described by C. Francis

Jenkins in the _Scientific American_ that seems to solve many of the

problems encountered in designing a two stroke cycle motor for

automobile purposes. As is well known, the present design of the

crank-case compression type is wasteful of fuel, and ignites irregularly

at low speeds and light running, and as nearly all automobiles are well

throttled for a greater portion of the time it means that this type of

motor is working under the greatest disadvantage.

[Illustration:

Fig. 66. Jenkins Two Stroke Cycle Motor.

]

Since the greater part of the trouble is due to the dilution of charge

by the residual gases, and as the spark plug of the motor is situated in

the most diluted portion of the gas, it would seem that a change of

spark plug location, or a change in the circulation of the fresh mixture

in the cylinder would be a great aid in remedying the difficulty. With

the spark continually in contact with fresh undiluted mixture it would

be possible to run it as low speeds as with the four stroke motor, with

a corresponding increase in the efficiency, and opportunity to run with

a constant advance of the point of ignition. This is accomplished by any

or all of the following conditions:

(1.) By keeping good gas separate from bad.

(2.) By placing the spark near the intake port.

(3.) By leaving the plug in its present position and deflecting the

fresh gas to meet it.

(4.) By changing the location of the inlet port.

[Illustration:

Fig. 58-a. Two Cylinder Marine Engine, of the Two Stroke Type. Built

by Fairbanks-Morse and Company.

]

In the motor invented and described by Mr. Jenkins, the method given by

(4) is adopted as shown by Fig. 66, in which the spark plug is placed at

the point of admission of the gas and in a confined passage. The

operation of the motor is as follows:

Carbureted gas is drawn into crank-case from the carburetor (not shown)

in the usual manner, i. e., by the upward movement of the piston; and by

its downward movement is forced through the rectangular port in the wall

of the piston into the combustion passage within the water-jacket when

the port in the piston wall registers with the lower end of this

combustion passage, and drives ahead of it the bad gas remaining after

the previous explosion. If the throttle is wide open the combustion

space above the piston will be completely filled, and on the ignition of

the charge the maximum pressure will be exerted on the piston. If,

however, the throttle is but slightly open, the combustion passage only

may be filled and none overflow into the combustion space above the

piston. This small charge will be just as efficient in proportion to its

volume as was the large charge, for it was compressed to practically the

same extent and none was mixed with the bad gas of the previous

explosion. It will, therefore, be obvious that the spark-plug is always

swept by the fresh charge, be it large or small, and the ignition will

be just as certain in one case as in the other, although the charge and

consequent impulse may be only just sufficient to keep the engine

turning over, and without missing a single explosion.

[Illustration:

Fig. 64-d. Roberts Cylinder Showing Cellular Screen in the Intake

Port. This Screen Prevents Crank Case Fires by Chilling the Cylinder

Flame Before it Enters the Crank Case.

]

In the motor built to test and demonstrate this design, provision was

made for a second spark-plug to be located in the top of the cylinder

for speed work, if this was found necessary. No opportunity has yet been

had for making track tests, though without regret, as this two-cycle

motor will run idle without missing or “stuttering,” which was the thing

heretofore impossible.

CHAPTER VII

OIL ENGINES

(31) Diesel Oil Engine.

The Diesel engine marks the greatest progress in the internal combustion

field made in the last few years. It marks a distinct advance in both

thermal efficiency, and in the character of the fuel that it has made a

commercial possibility. By the use of cheap fuel heretofore unavailable

for any type of prime mover, such as the asphaltum residual oils, coal

tar, etc., it has lowered the cost of power production to a point where

it is unapproached by any type of heat engine. Besides its thermal

efficiency, the engine is free from the annoyances due to delicacy of

the auxiliary appliances such as the carburetor, and ignition system

which are indispensable with the ordinary type of gasoline engine.

This engine belongs to that type of engine in which combustion takes

place at constant pressure (Brayton Cycle), that is the combustion

pressure is maintained at a constant value for a considerable distance

on the working stroke of the piston. This method differs from the Otto

cycle in which the combustion proceeds at a constant volume, or the type

in which combustion is completed before the piston moves forward on the

working stroke.

In the Diesel cycle the first stroke of the piston draws pure air into

the cylinder; the piston then moves forward on the compression stroke,

compressing the air to 500 or 600 pounds per square inch and raising the

temperature of the air to about 1,000 degrees C, the exact temperature

and pressure depending on the character of the fuel used in the engine.

The high pressure is obtained by using a small clearance space in the

end of the cylinder. At the end of the compression stroke a spray of oil

is injected into the cylinder which is instantly ignited by the high

temperature of the compressed air.

The oil continues to burn as long as it is sprayed into the cylinder,

this period being from one-quarter to one-third of the working stroke.

After the oil is cut off, the hot gas is expanded to the end of the

stroke at which point the pressure is very considerably reduced due to

the mechanical work performed. It should be noted that the type of

engine just described performs the complete cycle in four strokes, the

fourth stroke being the scavenging stroke as in the ordinary four stroke

cycle engine. While the four stroke cycle type of Diesel engine is by

far the most common type, it is also built as a two stroke cycle that is

similar to the two stroke cycle gas engine previously described except

that pure air is received and compressed in the air compressor in place

of the combustible mixture.

[Illustration:

Fig. 9. Cross Section of Four Stroke Cycle Diesel Engine. The Center

Valve is the Fuel Admission Valve.

]

It will be noted, that as there is no fuel in the cylinder during the

compression stroke that there is no danger from preignition from an over

heated charge, nor is there trouble from decomposed fuels due to a

gradually increasing temperature so often met with in oil engines that

compress the entire mixture. As the clearance space is exceptionally

small there is a minimum of residual gas held in the cylinder after the

explosion with the result that the fuel is completely consumed, and that

a full charge is taken into the cylinder.

The speed and output are regulated by controlling the point in the

working stroke at which the oil spray is cut off, and as this has no

effect on the maximum pressure developed in the cylinder, as in the case

of the ordinary gas engine control, the pressure charge under varying

loads is not so severe. Because of the high compression, and the

continued combustion, there is a very gradual increase of pressure.

Since the amount of pure air admitted to the cylinder is the same at no

load as at full load there is always sufficient air for the complete

combustion of the fuel, and as there is a constant compression pressure

there is a constant ignition temperature and constant quantity of the

working medium. Because of the high compression obtained by the Diesel

type, it has an efficiency that is far beyond that of any other form of

internal combustion motor.

[Illustration:

Fuel Nozzle of the Koerting Diesel Engine Showing Operating Cam and

Lever, and Compressed Air Connection.

]

Since the fuel is introduced gradually into the combustion chamber the

combustion pressure rises very slowly so that it is not an explosive

engine in any sense of the word, the combustion pressure rising steadily

from the compression pressure to the maximum in proportion to the supply

of fuel. In the ordinary type of gas engine with a compression pressure

of from 60 to 70 pounds per square inch the pressure rises abruptly to

about three and one-half times the compression pressure, with a

correspondingly rapid drop in the pressure on the expansion stroke. In

the Diesel engine the drop of pressure in expansion is much more

gradual, the indicator diagram expansion curve being nearly horizontal.

The uniform pressures thus obtained result in smooth action and even

driving power, obtained with no other type of engine.

[Illustration:

Fuel Pump of Koerting Diesel Engine with Operating Cam.

]

As the fuels used vary from the lightest hydrocarbons to the heaviest

crude oils, there are many types of oil injection valves in use, the

valves being in general divided into two classes, those in which the oil

is vaporized mechanically by the pressure of a force pump, and those in

which the fuel is vaporized by the atomizing effect of compressed air.

Atomization by compressed air is however, the most common method since

less trouble is experienced with the air pumps than with the liquid

force pumps. The compressed air is supplied by pumps that are either

operated by the main engine or by an independent compressor engine.

The fuel valve is a plug screwed into the cylinder containing an

inwardly opening check valve in the inward end. The hole in the center

of the plug receives the oil charge under a few pounds pressure from the

tanks, during the compression stroke of the engine, and at the end of

the compression stroke, a blast of air at a pressure of about 250 pounds

above the compression pressure blows it into the cylinder in the form of

a fine spray. Injection valves of the forced feed type consist of a plug

with a small passage and a needle valve for regulating the spray. Fuel

is pumped into the valve at about 250 pounds above the compression

pressure of the engine by a small single acting pump which is built so

that the length of the stroke may be adjusted to meet the load. In

practice the length of stroke is regulated by the governor, so that the

full contents of the pump are delivered at full load, and a reduced

amount with a short stroke at small loads. On issuing from the fuel

nozzle, the liquid strikes a gauze screen by which it is broken up into

very fine spray.

Fluidity is practically the only factor that governs the quality of fuel

that may be used with the engine, since exceptionally heavy oils and

tars cannot be successfully sprayed. In Fig. 9 is shown a cross-section

of a Diesel engine cylinder in which the center valve in the cylinder

head is the fuel valve, and the valves to the right and left are the air

inlet and exhaust valves respectively. The two latter valves correspond

to the inlet and exhaust valves of the Otto cycle engine.

Compressed air is used in starting the engine, which is admitted to the

cylinder through an auxiliary valve which is operated by a starting cam

on the cam shaft. By this mechanism, high pressure air is furnished to

the cylinder during a portion of the working stroke, turning it over on

the first few revolutions as a common air engine. As soon as the engine

picks up speed, the starting valves are thrown out of operation, and the

engine proceeds on its regular working cycle with the oil fuel.

When used for marine purposes in sizes over 100 horse-power, where it is

not possible to use reverse gears, the Diesel engine whether of the two

stroke cycle or four stroke cycle type must be made reversible. This may

be accomplished by either of two methods, first, by changing the angular

position of the cams in regard to the piston position, and second by

using two sets of cams, one being for right hand rotation and the other

for left hand. When a single cam is used, the relation of the cam shaft

on which the oil pump cams and oil valve cams are located, is advanced

or retarded in respect to the crank shaft by means of sliding the two

spiral gears that drive the cam shaft, over one another, in a direction

parallel to their axes. The spiral gears are moved back and forth by a

hand controlled reverse lever. This type is used principally on the two

stroke cycle type of engine as there are not so many factors to contend

with as on the four stroke cycle.

With double cams, the system almost invariably used with the four stroke

cycle engine, the cams may be mounted either on one shaft, or the ahead

cams on one cam shaft and the reverse cams on another. When two shafts

are used they are arranged so that either set of cams may be swung under

the valve lifters by swinging the shafts in a radial direction by

brackets. The single type of cam shaft is usually moved back and forth

in a direction parallel to its axis, the ahead cams coming under the

valve lifts at one position, and the reverse cams at the other. In the

four stroke cycle Diesel it is evident that not only the relations of

the oil pump and oil valves must be changed in respect to the piston

position but the relations of the air inlet and exhaust valves must be

changed as well. This necessitates double cams for the inlet and exhaust

valves in order to reverse rotation.

Compressed air for starting and injection is generally supplied by a

three stage air compressor or a compressor in which the pressure is

built up in three different steps, the second cylinder taking the air

from the discharge of the first, and the third cylinder taking the air

from the second, and compressing it to about 250 pounds above the

compression pressure of the engine. Perfect scavenging is possible with

this engine because of the large excess of air supplied during the

suction stroke and the period of injection. On the marine type the air

pumps and water circulating pumps occupy about the same amount of space

as the condenser and circulating pumps of a steam engine having the same

outputs. In a recent test made with an Atlas-Diesel engine it was found

that 11 per cent of the output was lost in driving the air pumps or more

than 50 per cent of the total loss by friction and impact.

[Illustration:

Fig. 67. Cross-Section Through the Working Cylinders of the M. S.

Monte Penado Two Stroke Cycle Diesel Engine. From the _Motor Ship_,

London.

]

Unlike the ordinary gasoline engine in which an increase of speed

increases the output in an almost direct proportion, the output of the

Diesel engine decreases when the speed rises beyond a certain limit due

to imperfect combustion at speeds much over 350 revolutions per minute.

Because of this fact it has been practically impossible to apply the

type to automobile service which ordinarily requires a speed of from 400

to 800 revolutions per minute under ordinary conditions. In addition to

the speed limitations, the Diesel engine weighs approximately 70 pounds

per horse-power against an average weight of 17 pounds per horse-power

with the ordinary type of gasoline automobile motor. Of course these

objections may be overcome in time, as the engine is only in its

infancy, and the two stroke cycle Diesel has not yet been fully

developed, but at the present time it does not seem probable that this

engine will ever be an active competitor of the gasoline automobile

motor, at least from the standpoint of flexibility.

As the Diesel engine depends entirely upon compression for its

operation, it is necessary that all of the parts such as the pistons,

valves, etc., shall be perfectly fitted and air tight under extremely

high pressures. The careful workmanship required for such fitting and

the adjustments make the Diesel much more expensive to build than the

ordinary type of gas engine, and for this reason the first cost and

overhead charges cut into the fuel item to a considerable extent. A

description of the Diesel engines will be found in the chapter devoted

to oil engines.

(63) Diesel Engine (Marine Type).

As a practical example of a Diesel engine, which was described in

Chapter III, we will give a brief description of the two 850 horse-power

Diesel engines installed in the cargo vessel “M. S. Monte Penedo,” which

were built by Sulzer Brothers of Winterthur, Switzerland. We are

indebted to the _Motor Ship_, London, for the details.

The engines are of the two stroke cycle, single acting type, with four

working cylinders, a double acting scavenging pump cylinder, and a three

stage ignition compressor cylinder. The bore of the working cylinders is

18.8 inches, and the stroke 27 inches. While the crank case is of the

enclosed type, there are two sets of covers which can be easily removed

for inspection while the engine is running, for as the scavenging pump

performs the work of the crank case of the ordinary two stroke cycle

engine there is no need of a tight case to retain the compression.

[Illustration:

Fig. 68. Cross-Section Through the Air Cylinders of the Two Stroke

Diesel Motors on the M. S. Monte Penado.

]

The scavenging pump is mounted on one end of the engine and is driven

from the crank-shaft, the cross-head of the pump forming one piece with

the piston of the low pressure cylinder of the injection air cylinder.

All of the compressor stages are water cooled and fitted with automatic

valves. The double acting scavenging pump has a piston valve driven by a

link motion for reversing it when the engine is reversed. The air enters

the pump through the top valve chamber from a pipe leading into the

engine room. The air discharges a pressure of about 3 pounds per square

inch in a header that passes in front of all four working cylinders. By

means of a valve the air entering the low pressure stage of the

compressor can be taken either from the atmosphere or from the discharge

of the scavenging pump; taking the air from the latter allows of a

greater weight of air taken by the compressor and consequently a higher

compression for use in emergencies.

As in the ordinary type of two stroke cycle engine, two independent sets

of exhaust ports are used, one set being for the scavenging air and the

other for the exhaust gases, both sets being at the end of the stroke as

usual. The air inlet ports are divided into two groups, however, one

group being controlled by the piston of the working cylinder, and the

other group by an independent piston valve driven from the cam-shaft.

Both sets of ports connect with the main scavenging air header. By means

of the valve controlled ports it is possible to admit scavenging air

even after the other ports are closed by the piston, which greatly

increases the scavenging effect. With the air at 3 pounds pressure the

air from the valve controlled ports throw the scavenging air to the top

of the cylinder even after the exhaust ports are closed. This valve is

provided with a reverse mechanism. A single cam is used for operating

the fuel inlet valve and the air starting valve, and the reversal of the

engine is obtained by turning the cam shaft through a small angle

relative to the crank-shaft, which of course also reverses the lead of

the fuel valve. Starting is accomplished by compressed air, with the air

valve lever on the cam, and the fuel valve lever off. After turning

through a few revolutions, the air valve levers are raised, and the fuel

levers dropped back on the cams which results in the engine taking up

its regular cycle.

By moving the tappet rod of the fuel valve out of or into a vertical

position, the time of the fuel valve opening is regulated and the amount

of air is controlled. This movement is normally performed by a

compressed air motor, but in an emergency hand wheels may be used.

One of these serves to rotate the camshaft through the required angle in

order to set the cams in the positions for astern or ahead running and

also reverses the link motion of the scavenging pump valve by the

rotation of shaft, as mentioned above. The other auxiliary motor

operates the fuel and starting air valves by moving the small spindle

longitudinally to bring the tappet lever of the air valve about the

required cam for ahead or reverse and also lifts this or the fuel valve

tappet rod off its cam, according as it is desired to run on fuel or

air.

The spindle on which the valve levers are pivoted is in two parts,

divided at the center. This is to allow two of the cylinders to run on

air whilst the other two are running on fuel, and, as can be seen from

the dial where the pointer indicates the position, in starting up,

whether astern or ahead, first two cylinders are put on air, then four

on air, next two on air and two on fuel, and finally all four on fuel.

This allows very rapid attainment of full speed.

The amount of fuel entering each cylinder can be regulated separately by

small hand wheels.

Below the fuel pumps are arranged three auxiliary pumps, two of these

being oil pumps for the oil circulation, whilst the other is of the

piston cooling water. On the left of the engine and driven in a similar

manner from the cross-head by links are three other pumps, one for the

circulating water and the other for the general water supply of the

ship.

Lubrication for the cylinders is furnished by 8 small pumps, just above

the water pumps, two oil pumps being provided for each cylinder. As the

supply pipe is divided into two parts, the oil reaches the cylinder at

four points in its circumference. Four oil pumps are provided for the

air compressor.

Four steel columns are provided for the support of each cylinder in

addition to the cast iron frame of the base, and by this means the

explosion stresses are transmitted directly to the bed plate. The cast

iron columns provide guide surfaces for the cross-head shoes. The guides

are all water cooled.

(64) The M.A.N. Diesel Engine.

The Maschinenfabrik Augsburg-Nürnberg, A. G., a German firm have built

some remarkably large Diesel engines both of the vertical and horizontal

types. The peculiar merits of the horizontal type of Diesel engine of

which the M.A.N. company are pioneers are still open to discussion at

present, but there is no doubt but what this type will be the ultimate

form of very large engines when certain alterations are made in the

design.

[Illustration:

Fig. 69. Horizontal M. A. N. Diesel Engine at the Halle Municipal

Plant.

]

[Illustration:

Fig. 70. High Speed Mirlees-Diesel Engine.

]

In Fig. 69 is shown a 2,000 brake-horse-power horizontal M.A.N. Diesel

engine of the four stroke cycle type which is installed at the Halle

Municipal Electricity Works, Halle, Germany. It is of the double acting

type with twin-tandem cylinders giving four working impulses per

revolution. This engine was installed in addition to the six producer

gas engines already in place to take the peak load of the station at

different times during the day, the gas engines meeting the normal

steady demand.

This firm has built many thousands of the vertical type of Diesel engine

of all sizes, and has recently installed 13 engines of 4,500 brake

horse-power for operating the Kreff tramways. The company is now

building cylinders giving outputs of from 1,200 to 1,500 brake

horse-power per cylinder, giving outputs of from 5,000 to 6,000

horse-power in tandem twin type engines. As will be seen from the cut,

the horizontal Diesel engine is remarkably free from complicated valve

gear.

(65) Mirlees-Diesel Engines.

The Mirlees-Diesel engine is built by the English firm, Mirlees,

Bickerton and Day both for stationary and marine service. A generating

plant consisting of two, 200 horse-power Mirlees engines direct

connected to Siemens generators has been installed in the municipal

plant at Dundalk as shown by Fig. 71. On test these units consumed 0.647

pounds of oil per horse-power at full load and 0.704 pounds per

horse-power at half load with a regulation of 3.24 per cent from full

load to no load. All of the engines built by this firm are of the four

stroke cycle type.

[Illustration:

Fig. 71. Mirlees-Diesels at Dundalk.

]

(66) Willans-Diesel Engines.

The Willans-Diesel engines built by the Willans and Robinson Company of

Rugby, England, are in sizes up to 400 brake horsepower, and run at

speeds up to 250 revolutions per minute. They are all of the four stroke

cycle type and are applied principally to the driving of electric

generators. The cut shows one of the four, 280 horse-power units

supplied to the Alranza Company and the Rosario Nitrate Works in South

America.

[Illustration:

Fig. 72. Willans Vertical Diesel Engine.

]

Unlike the Mirlees engine, the Willans has an individual frame for each

cylinder as in steam engine practice. Like the steam engine frame, the

bottom is left open for the inspection of the connecting rod ends and

the main bearings which is a most desirable feature. The air compressor

and pumps are arranged in a most compact form at the left end of the

crank-shaft from which the pipes may be seen issuing to the four

cylinders. The valves and over head gear are of the conventional type,

which, with the exception of a few minor details are the same as those

on the recently developed Sulzer-Diesel. The individual grouping of the

cylinder units has many desirable features and should, we believe, be

more extensively copied.

(67) Installation and Consumption of Diesel Plant.

An English gas-electric station was completed at Egham, England, that is

a good example of the changes that have been made recently in the

electricity supply abroad, with Diesel power.

The generating plant comprises two 94 K. W. Diesel engines built by

Mirrlees, Bickerton and Day, direct connected to single phase

alternators generating at 2,000 volts. The exciters are direct connected

to the main shaft, and the plant is capable of generating an overload of

10 per cent for two hours. Space has been left for the installation of

two more units of a larger size.

The following fuel consumption was guaranteed for a load of unity power

factor, and the official tests show slightly better figures than the

guarantee.

Full load 0.68 lb. oil per K. W. H.

Three-quarter load 0.72 lb. oil per K. W. H.

Half load 0.79 lb. oil per K. W. H.

Quarter load 1.15 lb. oil per K. W. H.

[Illustration:

Cross-Section Through Egham, England Municipal Plant.

]

Particular attention has been given to the water supply for the jackets

of the engines; the circulation being by two electrically driven, direct

connected centrifugal pumps, one of which is a spare. A Little Company’s

cooler has been installed, which consists of a horizontal cylindrical

chamber, the lower part of which contains water. In the tank are

arranged a number of concentric metal cylinders spaced about ¼-inch

apart, and in several sections, that are carried on a slowly revolving

shaft, driven from the fan shaft. The cylinders are all of the same

length, and are open at both ends.

The lower half of the cylinders dips into the water in the casing, and

as they revolve, a thin film of water on each side of the plate is

carried into the upper portion of the casing where it meets a blast of

cold air from the fan. The fan is driven from the circulating pumps, and

passes the air through the chamber in a direction opposite to that of

the water, baffles being placed so that correct circulation is

maintained.

The small loss is made up by connecting the ball cock in the tanks with

another tank charged from the works well by means of a self-starting

rotary pump, electrically driven. Very little power is required for the

pumps and cooler. Fuel oil is stored in a tank outside the building, the

oil being supplied to the tanks from an oil wagon by means of a small

hand pump.

Oil is taken from the tanks and forced into the engine room by a rotary

pump, from which it enters two graduated tanks located in the roof of

the station. The graduations on the tanks allow the consumption of oil

to be carefully recorded by alternately filling and emptying the two

auxiliary fuel tanks.

The entire building is electrically heated, and the kitchen of the flat

above the station is equipped with an electric cooking-stove for the use

of one of the engineers who make it his residence.

DIESEL HORSE-POWER FORMULA

P. A. Holliday, in the _Engineer_, derives a new formula for computing

the horse-power of the four stroke cycle, single-acting engine. For each

horse-power developed by these engines about 21,000 cubic inches of

displacement is necessary, per minute.

D = Cylinder bore in inches.

S = Stroke in inches.

M.P.S. = Mean piston speed in feet per minute.

R = Ratio of stroke to bore.

N = Revolutions per minute, then

√(B.H.P. × 2220)

D = ————————————————

M.P.S.

6 M.P.S.

Knowing the value of D, N = ————————

For high speed, low ratio (R), four stroke cycle engines, approximately

22,000 cubic inches displacement per minute is required.

√(2,330 B.H.P.)

D = ———————————————

M.P.S.

In both formulae, the air compressor for fuel injection is included.

(32) Semi-Diesel Type Engine.

In the “Semi-Diesel” Type Engine the oil is injected into the cylinder

at the point of greatest compression in the same manner as in the Diesel

engine, and like the Diesel it compresses only pure air. In regard to

the compression pressure, however, it stands midway between the pressure

of the Diesel engine and that of the ordinary “aspirating” type oil

engine, as the compression averages about 150 pounds per square inch.

While this is a much higher pressure than that carried by the ordinary

kerosene engine which compresses a mixture of kerosene vapor and air, it

is not sufficiently high to ignite the oil spray by the increase in

temperature due to the compression, but ignites the charge by means of a

red hot bulb or plate placed in the combustion chamber.

This type of engine is built both in the two stroke and four stroke

cycle types, the events occurring in the same order as in the two stroke

and four stroke Diesel types, that is, pure air is drawn into the

cylinder on the suction stroke (four stroke cycle) or is forced in at

the beginning of the compression stroke (two stroke cycle), and is

compressed in the combustion chamber. At the end of the compression

stroke, the fuel is injected against the red hot bulb or plate by which

the charge is ignited. Expansion follows on the working stroke after the

fuel is cut off, and release occurs at the end of the stroke.

Fuel oil is supplied to the spray nozzles by a governor controlled pump

having a variable stroke or by compressed air as in the Diesel engine,

making the supply of fire proportional to the load. A separate pump is

generally supplied for each cylinder, which is capable of developing a

pressure of about 400 pounds per square inch. Several of the Semi-Diesel

type engines have water sprayed into the cylinder for the purpose of

cooling the cylinder and piston, and as an aid in the combustion. This

water spray increases the output of a given size cylinder by the amount

of the steam formed by the heat of the cylinder and piston walls, and by

the increased rate of combustion. The amount of water supplied to the

cylinder is equal, approximately to the amount of fuel oil. The water

connection is made in the air intake pipe so that the water spray and

the intake air are drawn into the cylinder at the same time.

There is very little difference in the efficiency of the Diesel and

Semi-Diesel in favor of the true Diesel type for both have accomplished

records of a brake horse-power hour on .45 pound of crude oil in units

of the same capacity. Neglecting the question of efficiency the

Semi-Diesel has many advantages which are due principally to the

differences in compression pressures. Valve and piston perfection in

regard to leakage is not as essential with the semi-type as with the

Diesel, as the former is not dependent on compression for its ignition.

This means that the Semi-Diesel has a lower first cost and a lower

maintenance expense. Its low compression pressure makes starting

possible without the use of compressed air with engines of a

considerable horse-power. As the explosion pressure is much lower than

with the Diesel type there is less strain on the working parts and

lubrication is much more easily performed.

Compared with the ordinary type of kerosene engine the Semi-Diesel is

much more positive in its action as the oil is sure to ignite when

sprayed on the hot surface of the bulb or plate when under the

comparatively high compression. In the engine where the air is mixed

with the vaporized fuel before it is drawn into the cylinder, it is

difficult to obtain perfect combustion because of the uncertain mixtures

obtained on varying loads by the throttling method of governing. At

light loads the only difficulty encountered with the Semi-Diesel type is

that of keeping the igniting surface hot enough to fire all of the

charges.

In the majority of cases the two stroke cycle type of Semi-Diesel

engines compress the scavenging air in the crank chamber in the same way

that a two stroke cycle gasoline motor performs the initial compression,

although there are several makes that compress the air in an enlarged

portion of the cylinder bore by what is known as a “trunk” piston. This

initial compression determines the speed of the engine, the pressure

limiting the time in which the air traverses the cylinder bore and

sweeps out the burnt gases of the previous explosion.

(68) De La Vergne Oil Engines.

Two types of four stroke cycle oil engines are built by the De La Vergne

Machine Company, which differ principally in the method and period of

injecting the fuel into the cylinder. While both types compress only

pure air in the working cylinder, the oil is injected in a heated

vaporizer during the suction stroke in the smaller engine (type HA), and

is injected directly into the combustion chamber of the larger engine

(type FH) at the point of greatest compression. This fuel timing

classifies the type FH as a semi-Diesel, while type HA comes under the

head of that class of engines known as aspirators.

[Illustration:

76-a. Elevation of De La Vergne Oil Engine, Semi-Diesel Type. Class F

]

Semi-Diesel (Type FH)

During the suction stroke, air is drawn into the cylinder through the

inlet valve located on the top of the cylinder head, and on the return,

or compression stroke, the air is compressed to about 300 pounds per

square inch in the combustion chamber. The compression heats the air to

a high temperature which is still further increased by contact with the

hot walls of a cast iron vaporizer D, shown by Fig. 76-b. At the

completion of the compression, the fuel is injected in a highly atomized

state by compressed air through the spray nozzle F, the spray being

thrown into the vaporizer.

[Illustration:

76-b. Cross-Section of Type F H, De La Vergne Oil Engine.

]

The vapor formed by the contact of the spray with the walls of the

vaporizer mixes with the compressed air in the combustion chamber and is

ignited at the instant of fuel admission by the combined temperatures of

the vaporizer and compression pressure.

As the fuel is not injected until the proper instant for ignition, it is

possible to obtain a relatively high compression without danger of the

charge preigniting. The oil is supplied to the nozzle by a fuel pump

under pressure. The atomizing air takes the oil at pump pressure and

performs the actual injection. Details of the spray valve are shown by

Fig. 76, in which the oil and air are entered at a pressure of about 600

pounds per square inch.

[Illustration:

Fig. 76. De La Vergne Spray Nozzle.

]

The air and oil enter the nozzle at opposite sides of the cylinder B

which fits snugly into the valve body A. As the air and oil proceed side

by side along the outside of B, they are forced to pass through a series

of chambers connected by a system of fine diagonal channels on the

surface of B which results in a very fine subdivision and intimate

mixture. The charge is admitted to the cylinder by a sort of needle

valve about one-half inch in diameter which is provided with a spring

that holds it closed on its seat as shown by C, in Fig. 76. The needle

is so constructed that it may be readily removed at any time for

inspection. The spray valve is located on the right hand side of the

valve chamber directly opposite the vaporizer and is operated by an

independent cam on the camshaft.

[Illustration:

Fig. 76-c. De La Vergne Governor and Fuel Pump.

]

The vaporizer consists of an iron thimble having ribs on the inside to

increase the radiating surface. In starting, the vaporizer is heated for

a few moments until it reaches the temperature necessary for vaporizing

the fuel, but after the engine is running, the blast lamp is removed and

the temperature is maintained by the heat generated by the combustion of

the successive charges. Since the fuel is ignited at the instant that it

makes contact with the vaporizer, it is possible to accurately adjust

the point of ignition by adjusting the position of the fuel cam on the

camshaft.

Air for spraying the fuel is supplied by a two stage air compressor that

is driven from the crankshaft by an eccentric. The air compressed by the

first stage is stored in tanks at about 150 pounds pressure for starting

the engine. The second stage compresses the air to about 600 pounds

pressure, but is correspondingly small in volumetric capacity since it

handles only enough air to spray the oil which amounts to about 2 per

cent of the cylinder volume. A governor controlled butterfly valve in

the air intake pipe regulates the amount of air taken in on the second

stage to suit the varying charges of oil injected at each load.

In starting by compressed air, a quick opening lever operated valve on

the cylinder head is used to admit air from the tanks to turn the engine

over until the first explosion takes place. If the vaporizer is

sufficiently heated by the torch, the explosion occurs during the first

revolution of the crank shaft. At a point about 85 per cent of the

expansion stroke, the exhaust valve is opened, and the products of

combustion are expelled into the atmosphere. When starting, the

compression may be relieved by shifting the starting lever from the

exhaust cam to the auxiliary starting cam provided for that purpose.

Speed regulation is affected by a Hartung governor, driven from the

camshaft, which actuates the oil supply pump through levers by shifting

the point of contact between the pump levers and its actuating cam. This

lengthens or shortens the stroke of the pump in accordance with the

requirements of the load. The type FH engines are built in both single

and twin cylinders ranging from 90 to 180 horse-power in the single

cylinder type to 360 horse-power in the twin.

Since the fuel injection of the smaller engine type HA differs from that

just described, it will be described separately in the following

section.

The De La Vergne Oil Engine (Type HA)

In the small four stroke cycle De La Vergne Oil Engine, the fuel is

injected into a heated vaporizer during the suction stroke in such a way

that the vapor and intake air do not form a mixture in the cylinder

proper. On the return stroke of the piston, the compression of the pure

air takes place which forces the air into the vaporizer and into

intimate contact with the oil vapor. This forms an explosive mixture

which ignites and forces the piston outwardly on the working stroke. The

release and scavenging are performed in a similar manner to that of a

four stroke cycle gas engine. Both the inlet and exhaust valves are of

the mechanically operated poppet type, and as both the inlet and exhaust

gases pass through the same passage, the entering air is heated to a

comparatively high temperature.

The injection pump receives the fuel from a constant level stand pipe or

tank, located near the engine and injects the fuel into the vaporizer

through a spray nozzle. The vaporizer is a bulb shaped vessel that is

connected with the cylinder through a short post and really forms a part

of the combustion chamber. Since no water jacket surrounds the

vaporizer, it remains at a high temperature and vaporizes the oil at the

instant of its injection. Because of the residual gases remaining in the

chamber, ignition does not occur until air is forced through the passage

by the compression. The air inlet valve and the fuel injection valve are

opened at the same instant by a cam lever that also operates the pump.

On the compression stroke, the air which is at a pressure of

approximately 75 pounds per square inch enters the vaporizer, and

ignition occurs, partly because of the increased heat due to the

compression and partly because of the supply of additional oxygen.

Internal ribs provided in the vaporizer greatly increase the heat

radiating surface and add to the thoroughness with which the atomized

oil is vaporized. Since no mixture of air and fuel takes place in the

cylinder proper, sudden changes in the load do not affect the ignition

of the charge as the heated surfaces are surrounded with comparatively

rich gas under all conditions.

Before the engine is started, the vaporizing chamber is heated to a dull

red heat by means of a blast torch in order to vaporize the oil for the

first stroke. As soon as the engine is running, the lamp is cut out and

the temperature is maintained by the heat of the successive explosions.

The combustion attained by this method is very complete even with the

heaviest fuels, and whatever carbon deposit is formed occurs in the

vaporizer from which it is easily removed. The contracted opening of the

vaporizer passage effectually prevents the solid matter from working in

the bore or valves.

A Porter-type fly ball governor maintains a constant speed at varying

loads by regulating the quantity of fuel supply to the vaporizer, the

air intake remaining constant. A by-pass valve, controlled by the

governor divides the oil supplied by the pump, into two branches, one of

which leads to the spray nozzle and the other to the supply tank. In the

case where all of the oil is not supplied to the vaporizer because of a

light load, the by-pass valve will return the surplus to the tank, thus

maintaining a constant pressure at the spray nozzle.

When operating under ordinary loads, the governor opens only the small

inside valve which regulates the amount of oil injected into the

vaporizer. But should the engine speed up, due to a sudden change in the

load, the governor will not only open the small valve but also the large

concentric valve, in which case all of the oil will return to the tank.

The makers guarantee the following speed variation limits under the

different loads.

Ordinary Variation 2½ per cent.

Full load to one-quarter load 4 per cent.

Full load to no load 5 per cent.

(69) Operating Costs of the Semi-Diesel Type.

As the semi-Diesel type engine will operate successfully on the lowest

grades of crude oils, with an efficiency that compares favorably with

the true Diesel type, the operating expenses are very much lower than

with the gas or gasoline engine. With the same fuels, the semi-Diesel

will show greater net saving than the Diesel with a low load factor, as

the fuel saving is not eaten up by the high first cost, and overhead

charges of the true Diesel. Western crude oils with a specific gravity

of .960 (16° Beaumé) are being used daily with this type of engine while

nearly every builder of the semi-Diesel type will guarantee results with

oils up to 18° Beaumé (.948 Specific Gravity). Fuel of this grade will

cost anywhere from 1½ cents to 3½ cents per gallon in tank car lots,

depending on the distance of the engine from the wells or refinery.

With fuel oil weighing 7½ pounds per gallon, an engine consuming .65

pounds per horse-power hour (a usual guarantee) at full load, the cost

of a horse-power hour delivered at the shaft will be .26 cent with fuel

at 3 cents per gallon. This the lowest fuel expense of any prime mover

even with steam or gas units of great power. In a twenty-four hour test

of a De La Vergne oil engine running on 19° Beaumé oil, the consumption

was considerably below the figure assumed above, being .508 pounds per

horse-power hour. Even the engine was exceeded in a test made on a 175

horse-power engine by Dr. Waldo, which gave a consumption of .347 pounds

of oil per horse-power hour with oil of .86 Specific Gravity.

The following is a tabulation of reports received by the De La Vergne

Machine Company from the Snead Iron Works, giving the cost of power at

their plant under actual working conditions extending over a period of

twenty-four months. The plant consisted of a 17 × 27½ inch De La Vergne

semi-Diesel type engine of 180 horse-power rated capacity, the load

factor being 54.2 per cent. The total power produced during the record

was 552,217 horse-power hours, with a working period of 588 days. Fuel =

28.8° Beaumé = 7.35 pounds per gallon.

TABULATION

Items Total Cost Cost per Cost per

K.W. Hour H.P. Hour

Fuel Oil, 38,211 gallons $859.75 $.00232 $.00155

Lubricating Oil 228.72 .00061 .00041

Miscellaneous Stores and Repairs 123.20 .00032 .00022

Labor and Attendance 1361.42 .00368 .00246

——————— ——————— ———————

Total $.00693 $.00464

Fuel oil used = .761 pounds per K. W. hour = .508 pounds per horse-power

hour. Computing from the load factor of 54.2 per cent, the cost of power

produced under the above conditions would be $9.30 per horse-power year,

or $13.98 per kilowatt year. This result is obtained by assuming that

the horse-power hours would be increased from 552,217 to 1,077,354, or

in proportion to the actual load factor, the period, of course being the

same in both cases.

(70) Elyria Semi-Diesel Type.

A type of semi-Diesel type oil engine has been recently developed by the

Elyria Gas Power Co., Elyria, O., that presents many features of

interest. It operates on the two stroke cycle principle, and with the

exception of the spray nozzle has no valves in the working cylinder. The

principle of the semi-Diesel type cycle as distinguished from the true

Diesel engine, was described in Chapter III, as having the following

characteristics. (1) Fuel injection. (2) Medium compression pressure.

(3) Hot plate ignition. (4) An efficiency approximating that of the true

Diesel type.

[Illustration:

Fig. 77. Working Cylinder of Elyria Oil Engine.

]

It is claimed that the change from the ordinary four stroke cycle Diesel

cycle has been accomplished with practically no loss of thermal

efficiency, and that the elimination of the many moving parts of that

type has done away with many of the operating difficulties. By the

introduction of a false piston end and an unjacketed cylinder head, the

loss of efficiency due to the lower compression is compensated by the

reduction of heat loss to the jacket water. Because of the high

temperature it is possible to burn the heaviest fuels with a maximum

pressure not exceeding 400 pounds per square inch, and without trouble

due to missed ignition at light loads. With a given cylinder capacity

this heating effect has increased the output about 75 per cent. The loss

due to the friction of the scavenging apparatus causes a fuel

consumption of approximately 10 percent more than a standard four stroke

Diesel.

Unlike the Diesel, this engine automatically controls the quantity of

injection air admitted to the cylinder at different loads, the air

corresponding with the amount of fuel injected. This is in marked

contrast with the Diesel engine which admits a constant volume of air at

all loads. In place of the usual crank-case compression of the

scavenging air met with in the ordinary two stroke cycle engine, the

initial compression in the Elyria engine is performed by a “differential

piston” which acts in an enlarged portion of the cylinder bore. This

construction increases the volumetric efficiency from 70 percent, in the

case of the marine type, to well over 90 percent, and it also does away

with the bad effect of the compression on the lubrication of the main

crank shaft bearings.

[Illustration:

Fig. 78. Compressor Cylinder of Elyria Oil Engine.

]

The working piston and differential piston as shown by Fig. 77 is

separate castings fastened together by four studs, and the piston pin is

carried by the differential piston which acts as a cross-head, taking

all of the side thrust from the main piston. The working piston is

easily taken from the cylinder by removing the cylinder head and the

four nuts that fasten it to the differential piston casting. The

displacement of the differential piston is approximately 1.9 times the

displacement of the working piston which is more than enough for

thoroughly scavenging the cylinder and supplying air for combustion. The

air suction is controlled by a piston valve which eliminates much of the

loss encountered in the marine type of two stroke cycle.

In the figure may be seen the separate or auxiliary piston head which is

bolted to the piston proper, a construction that greatly increases the

working temperature, and allows a symmetrical form of piston. By

removing the cap over the inlet port, it is possible to inspect the

condition of the six piston rings with removing the piston from the

cylinder. Because of the clean burning of the fuel lubrication is easily

effected by the force pump which supplies oil at three points around the

cylinder wall.

Three stages of compression are employed for providing the air for fuel

injection, the first stage being accomplished by the differential

piston, and the remaining two stages by a separate air pump driven by an

eccentric from the crankshaft. This cylinder also supplies the air for

starting the engine, the air being taken from the second stage and piped

to the storage tank. The suction of the second stage pump which receives

its air from the differential pump (first stage) is controlled

automatically so that it is possible to keep the supply tank at any

desired pressure regardless of the pressure or amount of air used for

the fuel injection. Air from the tank (at approximately 200 pounds

pressure) is piped to the suction side of the third stage air pump. In

this suction line is a valve, controlled by the governor, which

regulates the amount of air admitted to the injection nozzle, and also

the amount. This pressure at the nozzle will vary from 500 pounds per

square inch to 1000 pounds depending on the load and the nature of the

fuel. The high pressure air travels directly from the pump to the fuel

valve casing, and is equipped with a safety valve and pressure gauge.

The fuel pump is driven by a Rites Inertia Governor located in the

fly-wheel which varies the stroke of the pump plunger and gives a

correct proportion of fuel to the load. This type of governor has been

extensively used on high speed engines and is exceeding accurate. The

fuel pump may be disconnected from the governor drive, and operated by

hand when it is necessary to provide fuel for starting. The spray or

injection valve is operated by a cam, which lifts the valve at the

proper moment in a very simple manner. The valve proper is made of a

single piece of steel with openings of ample size, so that there is no

danger of clogging with the heaviest fuels. As the valve only lifts 1/16

of an inch, the amount of work required to operate the valve is very

small.

Starting is accomplished by spraying cold gasoline into the cylinder

through the fuel valve in the same manner that the heavier oil is fed

during operation, and the ignition is performed by a high tension coil

and batteries. No spark time device is used, so that a continuous shower

of sparks is thrown into the mixture during the starting period. Within

a minute after the engine is started, the ignition switch may be opened,

the gasoline cut off, and the heavy oil turned on for continuous running

on full load. Starting by an electric spark avoids the inconvenience and

danger of torch starting with a retort.

Cooling water is admitted around the compressor cylinder from which

point it goes to the working cylinder, and is there discharged. Less

water is required for this type of engine than for the ordinary gasoline

engine, for with the water entering at 60°F, only 3 gallons per

horse-power hour is used. With fuel oil weighing 7.33 pounds per gallon

the makers claim a fuel consumption of .65 pounds per horse-power at the

rated load. The amount of cylinder oil used does not exceed 1 pint per

100 horse-power hours, while the loss of the bearing oil is extremely

small because of the return system.

(71) Remington Oil Engine.

The Remington Oil Engine is a vertical oil engine operating on the three

port, two stroke cycle, and is an oil engine in the strict meaning of

the word, the oil consumed being introduced into the combustion chamber

as a liquid and gasified within this chamber.

The method of gasifying and igniting the charge of oil in the Remington

Oil Engine is unique. Only clean air unmixed with any charge, is taken

into the crankcase. This air is afterwards passed up into the cylinder

and compressed until its temperature has raised to a point high enough

to vaporize the oil which is injected into it. The charge of oil is then

atomized into this hot compressed air and turns immediately into a

vapor, which finds itself well mixed with the charge of air, comes in

contact with a firing pin recessed in the head, ignite and burns. This

method of having the oil well gasified and mixed with air before

ignition begins, prevents the formation of carbon which is formed when

oil not well gasified and mixed with air comes suddenly in contact with

very hot surfaces.

This perfect system of gasifying the oil has the effect not only of

preventing the formation of carbon in the cylinder, but also of

increasing the mean effective pressure and therefore decreasing the

amount of fuel necessary for doing a certain amount of work. The engine

passes through its cycle of operations smoothly, and does not have to be

constructed with excessive weight.

[Illustration:

Fig. 79. Cross-Section of Remington Oil Engine.

]

The Remington Engine is of the valveless type, delivering a power

impulse in each cylinder for each revolution of flywheel. The gases are

moved in and out of the cylinder through ports uncovered by the movement

of the piston, which itself performs also the function of a pump.

On the up stroke of the piston a partial vacuum is created in the

enclosed crankcase, causing air to rush in when the bottom of the piston

uncovers the inlet port seen directly under the exhaust port (23), Fig.

79. On the next down stroke this air is compressed in the crankcase to

about four or five pounds pressure per square inch. Meanwhile the

mixture of oil vapor and air already in the cylinder is burning and

expanding. When the piston approaches the end of its down stroke, it

uncovers the exhaust port (23), permitting the burnt charge to escape,

until its pressure reaches that of the atmosphere. Directly afterward

the transfer port on the opposite side of the cylinder is uncovered by

the piston, thereby allowing a portion of the air compressed in the

crankcase to rush into the cylinder, where it is deflected upwards by

the shape of the top of the piston and caused to fill the cylinder,

thereby expelling the remainder of the burnt charge. The piston now

starts upward, compressing the fresh charge of air into the hot cylinder

head. Near the end of the stroke, a small oil pump, mounted on the

crankcase and controlled by the governor, injects the proper amount of

oil through the nozzle (13), into the compressed and heated air.

[Illustration:

Fig. 80. Remington Spray Nozzle.

]

This oil is atomized in a vertical direction through a hole near the end

of the nozzle. It is therefore vaporized and gasified before there is a

possibility of its reaching the cylinder walls.

The spray of oil is ignited by the nickel steel plug (12), which is kept

red hot by the explosions because the iron walls surrounding it are

protected from radiation by the hood (11). By the burning of the oil

spray in the air the pressure is gradually increased and the piston

forced downward, this being the power or impulse stroke. Near the end of

the down stroke, the exhaust port is again uncovered and the burnt gases

discharged.

[Illustration:

Fig. 81. Fuel Pump and Mechanism of Remington Oil Engine.

]

The operations above described take place in the cylinder and crankcase

with every revolution. Each upstroke of the piston draws fresh air into

the crankcase and compresses the air transferred to the cylinder. Each

down stroke is a power stroke, and at the same time compresses the air

in the crankcase preparatory to transferring it to the cylinder by its

own pressure at the end of the stroke.

The same volume of air enters the cylinder under all conditions, and the

power is regulated by modifying the stroke of the oil pump, which may be

done by hand or automatically by the governor in the flywheel. A

separate fuel pump is provided for each cylinder when multiple cylinders

are used, making it absolutely certain that each cylinder shall receive

the same amount of fuel for a position of the control lever.

When starting the engine, the hollow cast iron prong rising from the

cylinder head is heated by a kerosene torch, and when hot, a single

charge of oil is admitted to the cylinder by working the hand pump. The

flywheel is now turned backward, thereby compressing the charge which

ignites the fuel before the piston reaches the highest position. After

being started the engine, the torch may be extinguished.

[Illustration:

Fig. 82. Two Cylinder Remington Oil Engine Direct Connected to Dynamo.

]

The governor is of the centrifugal type. It has an L-shaped weight,

pivoted to the piece attached to the flywheel. As the engine speed

increases, the weight tends to swing outward toward the flywheel rim,

and thereby moves the arm attached to it so as to shift the cam along

the crankshaft toward the left.

This cam turns with the shaft, and operates the kerosene oil pump.

According to the position of the cam on the shaft, it will impart to the

pump plunger a long or a short stroke, thereby injecting more or less

oil into the cylinder. The lever pivoted on the bracket moves with the

cam and is used for controlling the engine’s speed by hand. To stop the

engine the handle of the lever is pulled towards the flywheel, thereby

interrupting the pump action altogether.

The handle of the control lever can be fitted with an adjustable speed

regulator when required. This device is for use on marine engines to

enable the operator to slow down the engine. The speed regulator does

not interfere with the action of the governor but acts in conjunction

with it. Whatever the speed of the engine may be, it is under the

control of the governor. The engine can be controlled from the pilot

house if such an arrangement is desirable.

The fuel pump is made of bronze. The valves are made of bronze and are

designed with very large areas. The plunger is made of tool steel. A

bronze cup strainer is attached to the lower end of the pump to prevent

sediment or foreign matter from reaching the pump valves. As a result of

the care used in its construction, the fuel pump is not only very

sensitive in measuring the oil required by the governor, but is also

very strong and durable.

The nozzle through which the fuel is atomized into the cylinder is

thoroughly water jacketed to prevent the formation of carbon within the

nozzle. It is so constructed that the water jacket spaces and fuel

spaces can be opened for inspection.

Lubrication of all the important bearing joints is effected by a

mechanical force feed oiler, pressure feed oiler or by gravity sight

feed oilers, depending upon the service for which the engine is

designed. Oil is fed in this manner to the piston, the main bearings and

the crankpin bearings. The oil for the crankpin is dropped from a tube

into an internally flanged ring attached to the crank by which it is

carried by centrifugal force to a hole drilled diagonally through the

crank and crankpin to the centre of the bearing. This insures that all

the oil intended for the crankpin shall reach it. This feature, as well

as the use of the sight feed oiler itself, is in line with the best

modern high speed engine practice, and is an important factor in the

reliability of the engine.

CHAPTER VIII

IGNITION SYSTEMS

(73) Principles of Ignition.

It is the purpose of the ignition system to raise a small portion of the

mixture to the combustion temperature, or the temperature at which the

air and fuel will start to enter into chemical combination. When

combustion is once started in a compressed combustible gas it will

spread throughout the mass no matter how small the original portion

inflamed. The rate at which the flame spreads through the combustion

chamber depends upon the compression pressure, the richness of the

mixture, the nature of the fuel and upon the number of points at which

it is ignited.

In practice perfect ignition is seldom realized. This is due not only to

the ignition system itself but to poor mixture proportions, imperfect

vaporizing of the fuel, and low compression; all of which tend to a slow

burning mixture with the attendant losses.

The best ignition system will be that which will cause the ignition to

occur invariably at the point of highest compression and which will

supply ample heat to start the process of combustion with a cold

cylinder, imperfect mixtures, and low compressions. An efficient and

reliable ignition system is without a doubt the most important unit in

the construction of a gas engine. As ignition systems have improved and

become more reliable, so has the gas engine become more widely used and

appreciated, and in almost a direct proportion to these improvements.

Many ingenious ignition systems have been proposed, but only two of

these have met with any degree of success in practice; i. e., electrical

ignition and ignition by means of the hot tube.

Sponge platinum has the peculiar property of igniting jets of hydrogen

gas, or hydrocarbons, without the aid of heat; this is due to the

condensing effect of the platinum on these gases.

It was proposed to ignite the gaseous charge of the gas engine by means

of the platinum sponge (catalytic ignition) but the system proved a

failure because of the clogging of the pores in the sponge by fine

particles of soot.

Dr. Otto employed an open flame which was introduced into the mixture by

means of a slide valve. This met with only a fair measure of success.

Cerium, Lanthum and several other rare metals cause a considerable spark

when brought into contact with iron or steel. The objection to this

method was the expense of the Cerium plugs which required frequent

renewal.

The writer remembers a quaint attempt at firing the charge by means of a

piece of flint and steel; the failure of this is obvious.

The Diesel Engine, a great success from a thermodynamic standpoint, is

fired by means of the heat produced by the compression of air, the fuel

being sprayed into air which is compressed to several hundred pounds

pressure.

Mr. Victor Lougheed proposes ignition by means of a platinum wire

rendered incandescent by a current of electricity. The plan sounds

feasible, but we are still waiting to be shown.

Electric ignition is applicable to all classes of engines; in fact this

system made the variable speed engine as used on automobiles, etc., a

possibility, as accurate timing with the electric spark covers the range

from the lowest possible speed to speeds of 4,500 revolutions per minute

and over.

(74) Advance and Retard.

While the combustion of the mixture is extremely rapid under favorable

conditions, there is, nevertheless, a perceptible lapse between the

instant of ignition and the final pressure established by the heat of

the combustion. For this reason it is necessary that ignition should be

started a certain length of time before the pressure is required if we

are to expect a maximum pressure at a definite point in the stroke of

the piston. The amount by which the time of ignition precedes that of

combustion is called the =ADVANCE=, and is usually given in terms of

angular degrees made by the crank in traveling from the time of ignition

to time of maximum pressure. Since the pressure is always required at

the extreme end of the compression stroke, the degree of advance is

given as the angle made by the center line of the cylinder with the

center line of the crank at the instant of ignition. Should the advance

be given as 10°, for example, it is meant that the crank is still 10°

from completing the compression when ignition occurs.

Owing to variations in the richness of the mixture, and changes in the

compression pressure, due to throttling the incoming charge, the rate of

inflammation varies from time to time under varying loads. To keep the

maximum pressure at a given point under these conditions it is necessary

to vary the point of ignition to correspond with the increase or

decrease of inflammation. This variation of advance to meet varying

loads is approximated by the governor in some engines, and manually in

others. The advance of an automobile is an example of manual ignition

control. Should the point of ignition vary from the theoretical point it

will result in a loss of fuel and power, and for this reason the

ignition should be under at least an approximate control. A wide

variation in engine speed has a very considerable effect on the ignition

point as there is less time in which to burn the mixture at high piston

speeds, and consequently the ignition must be further advanced to insure

complete combustion at the end of the stroke. This fact is evident to

those who have driven automobiles.

Should the ignition occur too early, so that combustion is complete

before the piston reaches the end of the stroke, there will be a loss of

power due to the tendency of the pressure to reverse the rotation of the

engine. When starting an engine, over-advanced ignition will throw the

crank over in the reverse direction from which it is intended to go, and

will not only prevent the engine from coming up to speed but will prove

dangerous to the operator.

Due to the effects of inertia and self induction in several types of

ignition apparatus, a greater advance will be required than that

demanded by the combustion rate of the mixture. This sluggishness of the

apparatus in responding to the piston position is called ignition =LAG=.

The total advance required to have the combustion complete at the end of

the stroke is equal to the advance required by the burning speed plus

the ignition lag. Since lag is principally due to inertia effects, it is

much greater at high speeds than at low, and it therefore causes an

additional advance at high speeds. Causing the ignition to occur before

the crank reaches the upper dead center is called =ADVANCED IGNITION=,

causing it to occur after the piston has reached the upper dead center,

or when on the outward stroke, is called =RETARDED IGNITION=.

Ignition is retarded when starting an engine to prevent it from taking

its initial turn in the wrong direction. As the combustion takes place

after the compression, with the piston moving on the working stroke, in

retard, it is impossible for the pressure to force the piston in any

direction but the right one. Excessively retarded ignition will cause a

power loss and will also cause overheating of the cylinder and valves as

the combustion is slower.

(75) Preignition.

Preignition which is in effect the same as over-advanced ignition as due

to causes within the cylinder such as incandescent carbon deposits or

thin sharp edges in the cylinder that have become incandescent through

the heat of the successive explosions. Preignition is very objectionable

since it causes heavy strains on the engine parts and causes a loss of

power in the same way as over-advanced ignition. Any condition that

causes the preigniting of the charge should be removed immediately.

(76) Misfiring.

The failure of the ignition apparatus to ignite every charge is called

=MISFIRING=. This missing not only causes a waste of fuel and a loss of

power but it also causes an increased strain on the engine parts because

of the violence of the explosion following the missed stroke. The heavy

explosion is due to the fact that the stroke following the “miss” is

more thoroughly scavenged by the two admissions of the mixture than the

ordinary working stroke, and consequently contains a more active charge.

(77) Hot Tube Ignition.

A combustible gas may be ignited by bringing it into contact with

surface heated to, or above the ignition temperature. It is upon this

principle that hot tube ignition is based.

In practice this surface is provided by the bore of a tube which is in

communication with the charge in the cylinder, the outer end of the tube

being closed or stopped up. Around this tube is an asbestos-lined

chimney which causes the flame from the Bunsen burner to come into

contact with the tube and also prevents draughts of air from chilling

it.

A Bunsen burner is located near the base of the tube and maintains it at

bright red heat. The gas for the burner is supplied from a source

external to the engine. When the fuel used is gasoline, a gasoline

burner is used, which is fed from a small supply tank located five or

six feet above the burner.

During the admission stroke, the hot tube is filled with the

non-combustible gases remaining from the previous explosion, therefore,

the fresh entering gases cannot come into contact with the hot walls of

the tube and cause a premature explosion, before the charge is

compressed.

As the compression of the new charge proceeds, the fresh gas is forced

farther and farther into the tube and at the highest point of

compression it has penetrated far enough to come into contact with the

hot portion. At this point the explosion occurs.

The tube being of small bore, does not allow of the burnt gases mingling

with the fresh within the tube; the waste gases in the tube acting as a

regulating cushion. The distance of travel of the new mixture is

proportional to the compression, hence the explosion does not occur

until a certain degree of compression is attained.

The length of the tube required for a given engine is a matter of

experiment, as is also the location of the heated portion. High

compression naturally forces the mixture farther into the tube than low,

therefore the flame should come into contact with the tube at a point

nearer the outer end with high compression than with a low compression.

Shortening the tube causes advanced ignition, as the mixture reaches the

heated portion sooner, or earlier in the stroke, because of the

decreased cushioning effect of the residue gases in the tube.

The length of tube and location of maximum heat zone should be so

proportioned that combustion will take place at the highest compression.

Moving flame to outer end of the tube retards ignition. Moving the flame

toward the cylinder advances it.

While the hot tube is the acme of simplicity in construction, it is not

the easiest thing to properly adjust, as the adjustment depends on

compression, temperature of the tube, and the quality of the mixture.

Any of these variables may cause improper firing.

The hot tube is rather an expensive type of ignition with high priced

fuel, as the burner consumes a considerable amount of gas, and is

burning continuously during the idle strokes as well as during the time

of firing.

It is practically impossible to obtain satisfactory results from a hot

tube on an engine that regulates its speed by varying the mixture or

compression, as engines running on a light load will not have sufficient

compression to cause the mixture to come into contact with the hot

surface, the engine misfiring on light loads.

The tubes are made of porcelain, nickel steel alloy, or common gas pipe,

and are of various diameters and lengths.

All of these materials have their faults. Porcelain being very brittle,

is liable to breakage. Gas pipe burns out and corrodes rapidly. Nickel

alloy is not liable to breakage, is not so susceptible to corrosion as

iron, but is far from being a permanent fixture.

Timing valves are a feature of some systems of hot tube ignition, which

correct to a certain extent the irregularity of firing of the plain type

of tube.

The timing valve is introduced in the passage connecting the cylinder

and tube, and prevents the gas in the cylinder from coming into contact

with the heated surface until ignition is desired.

The valve is operated by means of mechanism connecting it with the crank

shaft. It is evident that with sufficient compression in the cylinder,

the time of ignition can be obtained with certainty.

This mechanism is rather complicated, and subject to wear, and the

advantage gained by the fixed point of ignition is offset by mechanical

complication and consequent trouble.

The action of hot tube igniters is erratic and their use is not

advisable unless under unusual conditions. The open flame used in

heating the tube is a constant menace, as it is surrounded by

inflammable vapors. This feature alone condemns it in the eyes of the

insurance underwriters; in many places the use of the hot tube is

prohibited both by the underwriters and city ordinances.

The above inherent defects of hot tubes are supplemented by breakage,

“blowing,” and clogging of the tube or passage with soot and products of

corrosion, each factor of which will cause misfiring.

In case of misfiring, after determining that the tube is not broken or

clogged with soot or dirt, see that the engine is being supplied with

the proper mixture; that you are obtaining the proper compression; and

that the Bunsen burner is delivering a bright blue flame on the tube at

the proper point. Never allow the burner to develop a yellow sooty

flame. A yellow flame indicates that insufficient air is being admitted

to the burner. Remember that an overheated tube is quickly destroyed,

and will cause misfiring as surely as an underheated tube. Regulate the

gas supply to the burner.

A small leak near the outer end of the tube will destroy the cushioning

effect of the burnt gas, and hence will cause premature firing of the

charge. Procure a new tube.

Many engines are provided with a sliding burner and chimney which allows

of some adjustment of the flame on the tube. In cases of persistent

misfiring, move the chimney one way or the other. It may improve the

ignition.

(78) Electrical Ignition.

Ignition by means of an electric spark is by far the most satisfactory

method as it makes accurate timing and prompt starting possible. It is

the most reliable of all systems and is easily inspected and adjusted by

anyone having even a rudimentary idea of electricity or the gas engine.

For this reason electric ignition is used on practically all modern

engines (with the exception of the Diesel types). The spark is caused by

the current jumping an opening or gap in the conducting path of the

current, and the ignition of the charge is obtained by placing this cap

in the midst of the combustible mixture to which the spark communicates

its heat.

The method of producing the spark gap, and the method by which the

current is forced to jump the gap, divides the electrical ignition

system into two principal classes:

(1) The =MAKE AND BREAK=, or =LOW TENSION= system.

(2) The =JUMP SPARK= or =HIGH TENSION= system.

In either system the spark is produced by the electrical friction of the

current passing through the high resistance of the gas in the spark gap.

The incandescent vapor in the gap formed by this increase of

temperatures causes the flash that is known as the spark. The

temperature of the gap depends principally upon the current flowing

through it, the amount of heat developed being proportional to the

square of the current.

There is of course a practical limit to the amount of current used in

the ignition apparatus to produce spark heat. The limit is generally set

by considerations of the life of the battery furnishing the current,

expense of generating the current, and the life of the contact points

between which the spark occurs.

The heat developed by an electric current is proportional to the amount

of resistance offered to its flow and the strength of the current

employed. The greater the resistance, the more heat developed.

The resistance of copper wire (the usual conducting path), being very

low causes little rise in temperature, but the air in the opening or

break has a resistance of many thousands of times the resistance of the

copper; hence the current passing across the opening spark or gap raises

the air to an exceedingly high temperature.

With a comparatively heavy current flowing across the break, the

temperature developed is high enough to boil or vaporize any metal in

contact with the spark or flame, rendering the metallic vapors

incandescent. With sufficient current, the ends of the wires which

constitute the break may be melted away.

For the successful and continuous operation of the engine it is

imperative that ends of the conducting path or terminals be made of a

metal of a high fusing point in order to withstand the heat of the spark

and also that the current be kept to as low a value as possible.

In actual construction the spark gap terminals are generally made of

platinum or platino-iridium, or an alloy of high fusing point. Iron is

sometimes used, but deteriorates rapidly. Nickel steel lasts longer than

common iron or steel but is not as durable as platinum or its alloys.

As the temperature of the electric spark or arc is approximately 7,500°

F., and the ignition temperature of an ordinary rich gas at 70 lbs.

compression is 1,100° F., it is evident that the quantity of current for

ignition may be kept to an exceedingly low value. High compression

increases the resistance of the spark gap, and requires higher

electrical pressure to force a given current across a gap of given

length.

(79) Sources of Current.

The electric current that causes the ignition spark is usually generated

or supplied by one of the three following methods:—

1. By the primary battery which converts the chemical energy of metal,

and some corroding fluid, into electrical energy, by chemical means.

2. By the magneto or dynamo that converts mechanical work or energy into

electrical energy through the method of magnetic induction.

3. By the storage or secondary battery which acts as a reservoir or

storage tank for current that has been generated by either of the two

above methods. A storage battery simply returns electrical energy that

has been expended on it by an external generator. A storage battery does

not really generate electricity but as it is often used as a source of

current for an ignition system, we will consider it as a generator.

Current producers that convert chemical or mechanical energy into

electrical energy are called primary generators, and are represented by

the primary battery and dynamo. The above methods are used for

generating current for either the high or low tension systems.

Electricity may also be produced by friction, but as such current is

without heat value it is not used for ignition purposes. Electricity

produced by friction is called static electricity.

Primary and storage batteries always deliver a direct or continuous

current of electricity, that is a current which flows continually in one

direction. Dynamos are usually made to furnish a direct current, but can

be built to deliver either direct or alternating.

Alternating current, unlike the continuous current, changes the

direction of its flow periodically; flowing first in one direction and

then in the other, the flow alternating in equal periods of time.

Magnetos being a special form of dynamo can furnish either class of

current, but with few exceptions are built for generating alternating

current.

Either current may be used for ignition purposes for either high or low

tension systems.

Alternating current has several advantages not possessed by the

continuous current, when used for ignition purposes. The principal

advantages are:

1. Alternating current does not transfer the electrode metal of contact

points, and consequently causes less trouble with vibrators and “make”

and “break” ignitors.

2. Magnetos generating alternating current are less complicated, have

fewer parts to get out of order, and are cheaper to keep in repair.

3. Alternating current is not liable to burn out spark coils or overheat

with an excessive voltage.

4. Alternating current generators can be used at any speed without the

use of governors.

[Illustration:

43-a. The Esselbé Rotary Aero Motor. Four Pistons are Contained in the

Ring Shaped Cylinder at the Left Which are so Connected with Cranks

and Gears in the Gear Box that the Pistons and the Cylinder Rotate

in Opposite Directions. As the Pistons Rotate they also Oscillate

Back and Forth in Regard to One Another, so that the Working and

Compression Strokes are Performed. From Aero London.

]

When installing an ignition system give due consideration to the

reliability of the source of current. The gas engine is no more reliable

than its source of current. Failure of the current means the failure of

the engine.

(80) Primary Batteries.

Current is produced in a primary battery by the chemical action of a

fluid known as an =ELECTROLYTE= upon two dissimilar metals or solids

known as the electrodes. One of the electrodes, the negative, is usually

made of zinc which is more readily attacked by the electrolyte than the

positive electrode. As the metal of the negative electrode is dissolved

and passes into the solution during the process of current generation,

the electrolyte is also exhausted. The production of current is

accompanied by the liberation of hydrogen gas from the electrolyte from

which it is displaced by the zinc taken into solution.

When the electrodes are immersed in the electrolyte, and the outer ends

of the electrodes are connected with a wire, a current will flow from

the positive electrode to the negative through the wire, and from the

negative to the positive electrode through the fluid. It will be seen

that to complete the circuit between the electrodes it is necessary that

the current flows through the electrolyte.

Electrical energy is actually generated in the primary battery by the

chemical combustion of the negative electrode in the same way that heat

energy is developed by the burning of a fuel.

By connecting the binding posts of the electrodes to the two wires of

the external circuit, a current will flow through the circuit as long as

the electrodes remain undissolved, or until the positive electrode is

covered with hydrogen gas bubbles.

The bubbles of gas tend to insulate the positive electrode from the

electrolyte or fluid, thus breaking the circuit through the fluid, and

stopping the flow of current. This action is known as polarization.

When a battery is polarized, the only remedy is to disconnect it from

the circuit and allow it to rest or recuperate. The greater the current

drawn from a battery, the more rapid the polarization, and it is evident

that if the battery is to be used for long periods, polarization must be

eliminated, or the current must be considerably reduced in volume. A

battery that delivers a small current has a much greater capacity in

ampere hours than a battery that has a higher rate of discharge. The

greater the discharge rate the longer must be the rest periods.

A battery that is designed for continuous service, or for delivering

heavy currents of long duration, is called a closed-circuit battery.

Polarization is eliminated in closed circuit batteries by various

methods, the usual methods being to place some substance in the

electrolyte that will destroy the hydrogen film; or by packing some

solid oxidizing material around the positive electrode that will absorb

the hydrogen; or by making the positive electrode of some material that

will destroy the hydrogen as soon as it is developed.

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 17 / 20 章

Oil is supplied by a positive pump that measures the lubricant in exact