PETROLEUM ENGINES
There is a great deal of difference, from an economic point of view,
between spirit or carburetted air engines which we have just described
and motors using ordinary commercial petroleum oil. As a rule such
oil is much less dangerous, having a lower flashing-point, while at
the same time it is cheaper than the more artificial products such as
benzoline, naphtha, etc. We shall presently give a table comparing the
cost of power produced by various systems of motors, and which will
explain why the petroleum engine is gradually ousting the carburetted
air motor from its place.
The first motor using ordinary petroleum was brought out twenty-six
years ago by Brayton in 1872, and may be said to be the father of the
large family of motors which consume oils varying from naphtha to
others which have boiling-points as high as 150° C.
_Ready motor (Brayton)._—This motor belongs to the third group of the
table on page 21 (combustion and compression). There are two cylinders,
one motive the other auxiliary, and used for compressing air. The
compressed air passes through a space filled with some absorbent
material such as felt, and kept saturated with petroleum injected
into it by a special pump. The carburation of the air proceeds as
follows: the high-pressure jet of air causes the petroleum to froth
up, and in passing through it draws along a quantity of oil in the
shape of finely-divided particles. This petroleum mist passes on to
the cylinder. The advantage of this method of obtaining an explosive
mixture is that it matters not what oil is used, in fact, the heavier
oils are even to be preferred, as their partial condensation in the
cylinder helps to lubricate it. One volume of petroleum will by this
process produce 24,000 of explosive mixture.
The motor is constructed in both the horizontal and vertical form, the
auxiliary being superposed upon the motor cylinder. The admission of
the pulverized petroleum lasts for one-third of the forward stroke, and
the return stroke expels the burnt gases. The engine is double-acting,
using both sides of the piston.
A reservoir of compressed air is used for starting the engine, and
saves the trouble of turning the heavy fly-wheel round by hand to give
it the necessary impetus.
The Brayton motors are constructed by an American firm from 1 to 10
horse-power. The cost of maintenance and fuel is moderate, rendering
them exceedingly practicable where coal gas or the lighter petroleum
are unobtainable. A later type than the one we have just described
appeared in 1890 which is slightly more economic, single-acting, and
uses the Otto cycle. The process for obtaining a spray of oil is also
much improved. Both the auxiliary and the motor cylinders are connected
by a beam and connecting rods to the shaft. A red-hot platinum tube
ignites the explosive mixture.
_Sécurité petroleum motor._—This engine was patented in 1887 by MM.
Belmont Chabout and Diedrichs, and appeared at the Paris Exhibition of
1889. An Otto cycle is used, and ignition is obtained by a platinum
capsule heated to incandescence by a jet of carburetted air which
passes through a spiral coil warmed by the waste heat of the cylinder.
This ignition tube is situated at the back of the cylinder, and is
placed in communication with it by a port and valve, which determines
the exact instant at which the explosion takes place. The petroleum is
vaporized by passing through pipes coiled up in a vessel traversed by
the heated products of combustion. The vapour thus formed has a high
enough pressure to draw air along with it as it passes across an air
space between two nozzles; an explosive mixture is therefore formed.
The motor is started by carburating a small quantity of air by means of
a reservoir containing a light oil, and this supplies sufficient energy
to work the motor until the spiral coils are hot enough to vaporize
the petroleum. The whole apparatus is rather complicated, especially
as there are two separate vaporizers using different oils. This
disadvantage, combined with only a moderate efficiency and a high prime
cost, has severely handicapped the engine.
_Priestman oil engine._—The first patent of this interesting engine
was taken out in 1886 by Messrs. Dent and Priestman. The engine as
a whole represents probably the highest point of perfection which
it is possible to attain to in this class of motor, and the general
arrangement is somewhat similar to that of Dr. Otto’s engines, but in
addition there is a very ingenious apparatus for working with heavy
petroleum oils. A single-stroke pump, driven by an eccentric keyed to
an auxiliary shaft turning half as fast as the main shaft, compresses
the air to a standard pressure (depending in value, on the size of
the engine) in a reservoir supplied with a governing valve and placed
near the front of the engine. This reservoir contains petroleum, and
the pressure of the air forces it up into a spray-maker, where it is
pulverized. From thence the petroleum spray passes to a vaporizer
heated by the waste gases, and becomes mixed with a certain volume of
air forming an explosive mixture, which is admitted to the cylinder
by an automatic valve. Compression and ignition take place in the
cylinder, and the waste gases escape through a valve worked by the
same eccentric which drives the air-pump. The number of parts of the
mechanism is by this means reduced to a minimum, and it is found that
this peculiar vaporizing process completely prevents the cylinder from
being fouled, as is usual when petroleum is heated to such a high
temperature, often decomposing it. The Priestman engine gave a fresh
lease to the life of oil motors, which had at one time been almost
abandoned by engineers. It is well adapted for all kinds of industrial
operations requiring powers of from 1 to 50 horse-power, and large
vertical engines have been constructed for marine purposes up to 100
horse-power, and have always given complete satisfaction to persons
using them. A few minutes are required for the apparatus to become
sufficiently heated to be able to start, after which the consumption of
fuel is about 380 to 500 grammes of petroleum per horse-power hour, or
about ·85 lb. The six-horse size weighs about 1½ tons. Ignition can
be had either electric or by a flame, according to the wishes of the
purchaser.
_Campbell gas engine._—Fig. 29 shows a very compact engine, built
by the Campbell Gas Engine Co. There are only three valves; the
admission valve is regulated by a centrifugal governor. The petroleum
is gasified in a vaporizer heated by a lamp. The speed is very
constant and the motor easily started.
[Illustration: FIG. 29.—Campbell Oil Engine.]
_Grob motor._—This engine is constructed in Leipzig and uses the Otto
cycle, and, like the motors already described, works well with ordinary
petroleum. The arrangement (Fig. 30) is vertical; the cylinder and
valve gear are supported on a hollow cast-iron column, which in turn is
bolted to a circular bed-plate. The shaft has on one side a fly-wheel
and on the other a pulley. The working valve parts are all situated
on the outside so as to be easily got at. The oil-pump marked in the
figure drives, the petroleum into a vaporizer, where it is broken up
into very minute drops. This oil spray becomes mixed with air, and
passes through a vaporizing tube heated by a flame. In the state of
vapour the explosive mixture passes into the cylinder, where it is
ignited at the right moment by a red-hot tube. In consequence of the
compression during a quarter of the cycle, the combustion is very
rapid, the power of these engines being very great for their size.
Ignition, and therefore the explosion, only takes place when the speed
falls below the normal. This regulation is obtained by a pendulum
governor, and ensures a very constant speed. The cylinder walls are
warm enough to make sure of ignition happening.
[Illustration: FIG. 30.—Section of a Grob Motor.]
All heat engines based on the principle of the explosion of a volume
of gas require an arrangement for drawing superfluous heat from the
cylinder, otherwise it would soon become red-hot. This cooling is
obtained in small engines by the circulation of air about a large
surface especially attached to the cylinder walls, but in larger
engines this means is insufficient, and it becomes necessary to use
water as a cooling agent. If water is laid on there is no difficulty
about this, but it occasionally happens that water is too expensive,
or that it is unobtainable; in such cases it is usual to erect a large
cylindrical reservoir of galvanized iron holding about ten litres of
water per horse-power of the engine. This reservoir is connected by
two pipes from the top and bottom to the water jacket of the engine
cylinder, and circulation takes place by the difference of density
of hot and cold water. In the Grob motor a somewhat different device
is resorted to. The water arriving from the jacket at a temperature
of about 70° C. is divided into a number of fine streams, which pass
up through a network inside the reservoir. At the same time a small
centrifugal pump driven by the engine forces in addition a stream
of air through the water; the effect is to cool the water before it
returns to the jacket to a temperature of from 80° to 90° Fahrenheit.
The Grob motor is built in the same manner as the Capitaine engine,
which we shall describe next, but it does not work either as smoothly
or efficiently as the latter engine. It possesses, in addition,
other faults which are objectionable. The vaporizing apparatus is
particularly troublesome, for the result of gasifying petroleum at such
a high temperature is very often to decompose it, and thereby foul the
cylinder and valve mechanism.
[Illustration: FIG. 31.—Exterior View of Grob Oil Motor.]
_Capitaine petroleum motor_ (Figs. 32, 33, 34).—More than seventeen
years have elapsed since Emile Capitaine, already well known for his
experiments on gas engines, first tried his hand at oil motors. His
first patent dates from the year 1879, and since that time he has
continuously worked at the subject, expending much patience and money
in order to produce a high-speed motor capable of using ordinary
petroleum of ·88 specific gravity. The result of his labours is a
machine which is excellent in all respects, requiring no igniting or
heating apparatus. In the earlier type it was found that the motor
would not work at less than three-quarters of its full load, because
when it was doing less work the vaporizer became cooled in the
intervals which occurred between the rarer explosions. This motor
could only work under certain conditions, and after further trials and
experiments Capitaine brought out a motor which worked at small loads
as well as full loads, and which only consumed fuel in proportion to
the power developed. This machine was considered too complicated, and a
fresh type was brought out.
[Illustration: FIG. 32.—Capitaine Gas Engine.]
[Illustration: FIG. 33.—Horizontal “Balance” Motor (Capitaine).]
This third engine has a vaporizer which is in permanent communication
with the cylinder, and is so constructed that even if it became red-hot
there would be no risk of pre-ignition or the formation of tarry oils
which would foul the cylinder. The vaporizer only draws in sufficient
petroleum at a time for one explosion, and then only during the
aspirating stroke of the piston. At the end of this stroke the whole
of the petroleum in the vaporizer is gasified. The first motor on
this plan was built by Capitaine in 1889, and many of them are still
constructed at the present date by M. Louis Herlicq of Paris.
[Illustration: FIG. 34.—Capitaine Two-cylinder Gas Engine.]
Capitaine came to an agreement with Grob et Cie. in order to exploit
his inventions in a wider field. Unfortunately differences arose,
and in 1891 the agreement was cancelled. A lawsuit followed, lasting
till March 26, 1893, when it was brought to an end by Grob et Cie.
agreeing to pay Capitaine the sum of 125,000 francs in consideration
for permission to use his name and patents in connection with their
motors. After breaking up the partnership with Grob et Cie., Capitaine
continued to build engines, and has since then taken out several
patents, which have considerably enhanced the value of his previous
inventions. In the 1892–93 type a lamp is used for starting which
can afterwards be dispensed with, the heat of the compression being
sufficient to maintain the temperature of the vaporizer. This is,
however, only if the motor is developing more than three-quarters
of its full power. When it was found that the same shaped indicator
diagram could be obtained from these motors even when they were giving
only 75% of their full power, it became obvious that it was only
necessary to keep the vaporizer as warm as possible by covering it with
non-conducting jackets, in order to get the engine to run at quite a
small fraction of its full power. Capitaine has, by carefully observing
this condition, obtained a motor which will run at all loads without
any external heating apparatus.
The vaporizer forms part of the combustion chamber, and is carefully
covered with non-conducting material. Only hot gases are allowed to
pass through it. It must be started by heating for a few minutes with a
small hand-lamp, and the engine is then ready for work.
_Merlin motor._—This motor is of the vertical type, and resembles the
Capitaine motor in some respects. The oil is stored in a reservoir in
the bed-plate; this receptacle is in communication with an air-pump
driven by the motor, and also with an oil-pump. The pressure of air
generated by the former forces the petroleum up into the oil-pump,
which in its turn passes it drop by drop through a pulverizer, after
which the spray of oil enters a vaporizer and becomes gasified. The
vaporizer is heated by a special petroleum lamp. Ignition takes place
when the explosive mixture comes into contact with the heated walls of
the vaporizer, their temperature being always high enough to ensure
ignition taking place. The consumption of fuel is regulated by a
governor acting on the oil-pump, preventing it from supplying more
oil than is absolutely necessary to keep up the speed. The governor
regulates the exhaust valve as well, so that the speed, which is pretty
high, is kept quite constant.
_Hornsby-Akroyd oil engine_ (Figs. 35, 36).—This interesting machine
was invented by Messrs. Akroyd, Stuart and Binney; it works with
ordinary petroleum, and without the help of a carburator uses oils
varying greatly in specific gravity. The reservoir of fuel is situated
in the bed-plate. The ignition is automatic, and an electric spark is
unnecessary, in fact, the whole engine is of the simplest construction,
in order that there may be no inconvenience due to breakdowns.
Referring to Fig. 35, L is a special petroleum lamp situated at the
back of the cylinder A. When starting this lamp is supplied with air
from a rotary fan turned by hand; in a short space of time, by the
help of this stream of high-pressure air, the cartridge C becomes
sufficiently heated to ensure the ignition of the explosive mixture.
This cartridge C is provided on its interior with radiating ribs, which
greatly increase the surface. During the back-stroke of the piston
it becomes filled with compressed air from the cylinder, and towards
the end of this stroke a quantity of petroleum, exactly sufficient
for the explosion, is squirted into it. To do this a small pump is
provided, which is actuated by a cam driving the oil into the cartridge
and brought back by a spring. The centrifugal governor G acts on the
admission valve from this pump. The sudden injection of the oil into
the middle of the heated chamber completely vaporizes it, forming
with the air already present the necessary explosive charge, which
immediately ignites in contact with the heated walls.
[Illustration: FIG. 35.—Hornsby-Akroyd Oil Engine (section).]
When the vaporizing cartridge has been sufficiently heated a rapid
turn of the fly-wheel by hand, so as to produce the first explosion,
is sufficient to start it, after which the vaporizer keeps itself
warm. The pump which keeps up the supply of oil will be seen in the
right-hand bottom corner of Fig. 35. It is of the plunger pattern, and
at every stroke of the piston draws in the right quantity of oil and
injects it into the vaporizer through a valve. The illustration on
page 91 shows the other side of the engine with the valve-shaft, which
revolves once for every two revolutions of the crank, also driving
the centrifugal Porter governor. If the speed should happen to exceed
the normal, a steel finger moved by the governor closes the valve
admitting oil to the vaporizer, which then returns to the reservoir,
having failed to accomplish its object. As the ordinary Otto cycle is
used, a heavy fly-wheel is necessary to maintain the speed constant
between the explosions. After being once started very little attention
is necessary, everything working automatically. A water jacket W cools
the cylinder.
[Illustration: FIG. 36.—Exterior View of the Hornsby-Akroyd Oil Engine.]
The specific gravity of the oil is usually about ·854, and of this
the engine consumes about one pint per hour per B.H.-P., at a cost of
1½_d._ An additional advantage of the high speed is, that there is
less chance of the cylinder becoming fouled by tarry products.
_Vulcan motor._—This engine is in many respects a counterpart of the
Akroyd motor. The cylinder is horizontal, and projects over the end
of the bed-plate. Two fly-wheels are provided if very steady running
is required. The lamp which vaporizes the petroleum at starting is
removed when once the normal speed is attained. A water jacket prevents
the cylinder from getting too hot. The most noticeable feature is the
rather curious arrangement for governing by means of bent oscillating
levers, which control both the admission and escape valves. The
governor itself is situated inside the transmission pulley and keeps
the speed within 1% of the normal; 600 grammes of petroleum per
hour per horse-power is the usual consumption. The motor is rather
too complicated, and can scarcely be said to have justified the
expectations formed of it.
_Ragot petroleum motor_ (Figs. 37, 38).—This engine, like the preceding
ones, uses heavy petroleum and particularly schistic oil, which has a
flashing-point above 77° Fahrenheit, and which may be bought very much
more cheaply than naphtha, benzoline, or other artificial products
of petroleum. Several different patterns of the engines are on the
market, of which certain ones are of great value for electric lighting
purposes, not only because of their steady running, but also because,
by burning cheap oil, they allow the cost per horse-power to be reduced
to a minimum. One high-speed pattern has been especially designed for
coupling direct to dynamos, forming a very neat and compact plant. The
latest developments in the construction of these engines tend to the
simplification of the parts, and they are now so free from unnecessary
mechanism, that persons with little or no knowledge of mechanics are
quite capable of looking after them, and even taking them to pieces
and putting them together again if a breakdown should occur, which is
unlikely.
[Illustration: FIGS. 37, 38.—Sections of the Ragot Petroleum Engine.]
By a special arrangement in the carburator all constituents of the
petroleum which might foul the cylinder are removed before the oil
is allowed to enter the cylinder, and therefore it seldom requires
cleaning out. The carburator (Fig. 39) is very ingeniously arranged;
it consists of a cast-iron cylinder smooth on the inside, but provided
with a spiral rib on its outer surface, and heated by an oil lamp. The
spiral rib is itself enclosed by a covering, so that it forms a spiral
tube. The petroleum is allowed to enter at the top, and gradually winds
its way down, passing over a continually warmer and warmer surface
as it approaches the lamp. The more volatile portions of the oil are
therefore vaporized first, and the heavier oil passes on and is not
vaporized till near the base, where the temperature is high enough to
gasify the heavy residue. The air is heated in a jacket surrounding the
base of the spiral, and is afterwards mixed with the oil vapour.
_Root motor._—These engines work with the ordinary four-cycle, and are
interesting because of the double-ignition apparatus. A lateral chamber
is attached to the cylinder, communicating with it by an orifice
situated at the back end, which is covered when the piston is at the
beginning of its stroke. During the compression stroke a portion of
the mixture is enclosed in this chamber and separated from the rest
of the charge, which is compressed and ignited in the ordinary way.
The explosion drives forward the piston, and when it has moved forward
some distance it unmasks the above-mentioned orifice, igniting the
gas contained in the lateral chamber, and helping to maintain the
pressure behind the piston. This addition to the pressure is noticeable
in a diagram taken from the cylinder, by sudden rise of pressure. We
don’t quite see the utility of this arrangement, which seems to merely
complicate matters. The first ignition is effected by a red-hot tube.
The Root vaporizer utilizes the heat of the exhaust gases; the air
is heated in a spiral coil wound round the tube through which the
vaporized oil passes. The two become mixed in a small vessel, and the
vaporizer is supplied by a chamber placed directly round the exit of
the exhaust gases. Strictly speaking, there is no oil pump, but a
plunger in a small auxiliary cylinder serves to direct the flow of oil
into the right channels. Admission takes place through an automatic
valve. The escape valve is actuated by the same mechanism which drives
the piston governing the flow of oil.
[Illustration: FIG. 39.—Carburator of the Ragot Oil Engine.]
_Koerting-Boulet motor._—In this four-cycle engine we shall only
describe the vaporizer and spray-maker. The oil is stored in a
reservoir placed about six feet from the ground, and a pipe conducts it
into a space between two discs with a valve at the top. This circular
space, about half a millimetre in thickness, is traversed by the air
which pulverizes the oil; the spray thus formed is vaporized by the
high temperature developed by a lamp situated underneath the tube which
conducts the carburetted air to the cylinder. In addition, this lamp is
used for igniting the gases through a porcelain tube kept at red heat
by it. An auxiliary spirit-lamp is used for starting the engine, which
takes about fifteen minutes to acquire a sufficiently high temperature.
_Knight gas engine._—In his endeavour to completely drive out the
products of combustion from the cylinder, Mr. Knight has had recourse
to the Griffin cycle and to a double-acting cylinder: we have
already discussed the relative merits of this system, and think it
is sufficient to point out the greater constancy of speed obtained
by it. The vaporizer is placed behind the motor-cylinder, and is
separated from it by a steel plate, so that it is maintained at a high
temperature; this vaporizer is made of bronze, and is provided with
radiating ribs. A pump injects oil into it, and it is also supplied
with compressed air by a special pump, which furnishes in addition a
jet for producing a blow-pipe flame. This flame white-heats a platinum
wire, which ignites the gases. The wire is situated in an opening in
the ignition valve; the valve moves forward, and the white-hot wire is
brought into contact with the explosive mixture at the right moment.
The admission valve is automatic, and situated in the steel plate
separating the vaporizer from the cylinder. The other organs of the
motor are not of any special interest.
_Crossley-Holt oil engine_ (Fig. 40).—This is practically the same
engine which we described in the chapter on gas engines; a vaporizer is
added in the oil motor to enable it to work with petroleum.
It consists of a chamber divided into four channels by vertical
partitions, and heated by a lamp placed underneath. The flame traverses
these channels before reaching the chimney placed at the top. The
petroleum is converted into a spray, and drawn off by a jet of air
warmed by passing it through a spiral coil placed round the lamp
chimney. This jet of air is supplied by a small pump worked by a lever.
The oil lamp has no wick, which is rather a novel arrangement: it is
supplied by a small pump similar to that which provides the air. Since
its first appearance this engine has undergone certain changes which
have considerably improved it. Messrs. Crossley Bros. have especially
devoted themselves to shortening the length of time necessary to heat
and start the engine. Besides this they have paid great attention to
simplicity of the working parts.
[Illustration: FIG. 40.—Crossley-Holt Petroleum Engine.]
_Trusty oil engine._—This motor was devised by Mr. Knight, and is
constructed by Messrs. Weyman and Hitchcock. There is no spray-maker,
the liquid oil being directly converted into vapour. The vaporizer is
heated by the waste gas from the cylinder, and the oil falls drop by
drop on to the hot metal walls and becomes vaporized. The engine is of
the ordinary four-cycle type, the most noticeable feature being the
governing arrangement; a governor of the inertia pattern regulating
the admission valve and the oil-pump. If the speed becomes too great
the action of the governor on the valves ceases, and oil is no longer
supplied to the vaporizer from the pump and the admission valve remains
closed. Ignition is obtained by a red-hot tube heated by an oil lamp;
a layer of asbestos on the outside prevents the tube from cooling, and
keeps the tube at a high temperature. It takes twenty minutes before
the vaporizer becomes sufficiently heated to enable a start to be made,
and the cylinder is very liable to become fouled by tarry products
from the oil. These serious disadvantages are scarcely neutralized by
the variety and small quantity of oils which the engine will burn. An
engine of this type with two cylinders consumed in certain trials only
half-a-pint of oil, which speaks for itself.
_Griffin oil engine_ (Figs. 41, 42).—Yet another Otto cycle engine
provided with a pump reservoir and vaporizer. The latter is hidden in
the bed-plate, and is heated by the gases from the exhaust. The pump
is driven by an eccentric on the main shaft, and compresses the air to
about 8 lbs. on the square inch in a reservoir also situated in the
bed-plate. The compressed air passes from this chamber into a needle
pulverizer, along with a quantity of oil which it has gathered in a
small ante-chamber. This pulverized oil arrives in the vaporizer at
the same moment as the air for the explosive mixture. A portion of
the vaporized oil and air is used for the lamp, which red-heats the
ignition tube. At starting, a small quantity of air is compressed in a
hand pump, and in ten minutes the vaporizer is hot enough to gasify the
oil. The Griffin engine is very economical, and only uses about a pint
of petroleum per horse-power hour.
[Illustration: FIGS. 41, 42.—Griffin Oil Engine.]
_Niel petroleum engine._—In these motors, the general arrangement of
whose parts is similar to that of the gas engines constructed by the
same firm, the principal part is the vaporizer. It consists of a small
cast-iron chamber, provided with radiating ribs in its interior so as
to increase the surface; the petroleum, coming from a reservoir placed
at a height of about six feet, passes through a regulating valve, and
is dispersed in fine drops over the surface of the radiating ribs;
the vaporization is consequently very steady. An automatic valve
allows air to pass into this chamber from the outside, forming an
explosive mixture with the vaporized oil. A special tube coming from
the reservoir supplies a lamp with oil for heating the ignition tube
and also the vaporizer at the same time. A methylated spirit lamp is
used for warming them up to the right temperature before starting the
engine. The governor acts on both the admission and the exhaust, and
the supply of oil is indirectly regulated by the closing of the exhaust
valve. The whole mechanism is ingenious, giving excellent results;
the speed is very constant, and the consumption of oil is within wide
limits proportional to the demand for power. About a pound of oil is
consumed per horse-power hour, including that necessary for the lamp.
Two patterns of this engine are built, one vertical and the other
horizontal. In the latter, called the Atlas engine, the consumption
per hour is slightly greater. The governor is also different. The
compression in the cylinder rises to about two atmospheres, and the
quantity of water necessary for the water jacket varies from seven to
ten gallons per horse-power hour, according to the size of the motor.