INTERNAL COMBUSTION ENGINES
In no other sphere of employment has petroleum made such rapid
strides during the past two or three decades as those recorded in
connection with its use in internal combustion engines, and one of the
most interesting features of modern mechanical engineering is their
development. The advent and immediate popularity of this kind of engine
has been responsible for some of the most remarkable conquests of
mankind over the forces of Nature, for it has brought into being the
automobile, the aeroplane, the dirigible airship, and a host of other
inventions. It has also been responsible for quite a new departure in
ocean transport, for experiments have proved that the largest vessels
can be very economically operated by means of the internal combustion
engine.
It might, by way of introduction, be well to explain for the benefit of
the uninitiated, the meaning of the term “Internal combustion engine.”
As most of my readers are well aware, the steam, or, rather, to be
exact, the highly heated water vapour which drives the steam engine,
is supplied from boilers which are heated by the burning of coal, oil
fuel, or, sometimes, gas, and such engines might, therefore, be called
“external combustion engines,” since the fuel is consumed in apparatus
external to the engine proper. Such a term, however, is not in use
amongst engineers, and might raise a superior sort of smile if used
in their presence. It will be readily seen from the foregoing that a
great deal of weight and apparatus of some complication is required
before the water vapour which drives the steam engine can even be
provided.
In the case of the internal combustion engine, the fuel (motor spirit
or the heavier oils) is introduced directly into the engine and there
vapourized and mixed with air so as to form an explosive mixture, so
that all boilers, with the necessarily complicated systems of piping,
etc., are done away with. It needs no imagination to understand the
enormous saving of weight and space resulting from this elimination of
the boiler, and of the room which it would occupy.
The latter-day demands for the provision of lighter and yet lighter,
as well as space-saving propelling machinery for submarines, airships,
aeroplanes, motor-cars, etc., especially during the war, have
enormously stimulated the development of the engine which consumes its
own fuel, and which is known as the internal combustion engine. A very
wide field has thus been opened out for the exercise of the engineer’s
ingenuity, and he has availed himself to the full of the opportunities
thus created, never failing to rise to the occasion when fresh demands
have been made upon him.
In these circumstances, it is not at all surprising to find that
numerous firms have given considerable attention to the manufacture
of the internal combustion class of engine, and many varieties,
for a multiplicity of purposes, are upon the market. The limits
of space effectively prevent my detailing the list of even the
largest manufacturers; I will therefore content myself by referring
to but one firm--Messrs. Vickers, Ltd.--who are now the largest
manufacturers in the Kingdom. This progressive firm has grappled with
the internal combustion engine problem from the earliest stages of the
petrol engine to the latest forms of the heavy oil engine and its
remarkable developments, and a large section of their establishment at
Barrow-in-Furness is, and has long been, set aside exclusively for the
design and manufacture of the heavy oil internal combustion engine. A
very large staff of expert engineers has been selected for the work,
while experiments with a view to improvements being effected in details
are continually being conducted in the establishment. The result is
that the development of this engine at the Barrow works has been
attended with the highest success, a fact which is not widely known to
the general public.
I take it as a great compliment that permission has been given me in
this book to refer somewhat in detail to the achievements of Messrs.
Vickers, Ltd., in this respect, for, hitherto, publicity in connection
with this section of the firm’s operations has been strictly withheld.
One of the latest and, it might well be said, the most important
developments in connection with Messrs. Vickers’ activities, is the
Vickers patent system of fuel injection, which enables an engine of the
Diesel type (that is, using heavy oil) to be successfully run without
the use of an air compressor for injecting the fuel into the engine.
Before the introduction of this system, an air compressor, with its
attendant complication and weight, had to be used for the introduction
of the fuel into the engine. The elimination of this compressor has
resulted in considerable economy in weight, space, and attendance,
which, it will readily be seen, is a step in the right direction,
whilst the efficiency of the engine has also been improved. The
disadvantages attendant upon the use of the air compressor were early
comprehended by Messrs. Vickers, and they have spared no efforts (nor
expense) in developing the system which has led to its elimination.
The reader will require no knowledge of the subject to understand that
the question of fuel consumption is one of the highest importance
in any engine system, and, in regard to this point, Messrs. Vickers
have made a special study, with the result that whilst the ordinary
consumption in a Diesel engine with air compressor is ·41 lb. brake
horse-power an hour (or 184 grammes _par force de cheval_), that firm
have been able to reach the low figure of ·376 lbs. B.H.P. an hour (or
·170 grammes _par force de cheval_).
As one might expect, Messrs. Vickers, in bringing their engine
to its present state of perfection, have, perforce, had a varied
experience with fuel oils--and a considerable one, too,--for they have
experimented with oils from all the well-known producing fields, and
find that, under their system, practically any fuel oil which can be
made to flow may be utilized in their engines--a fact which, in its
importance, speaks for itself. The physical properties of the oils used
by them have, naturally, differed very considerably. For instance,
specific gravities have varied from ·810 to ·950 flash points from 100°
Fahr., to upwards of 250° Fahr., whilst the viscosities, which the lay
mind might well be excused for thinking of as “degrees of stickiness,”
have varied from that of the ordinary kerosene (illuminating oil) to
the thick asphaltic fuel oil which comes from Mexico. Readers may judge
from this of the painstaking and difficult experiments that have been
carried out in the Barrow works.
The advantages derivable from the use of the Vickers system could not,
obviously, be withheld from general use, and the firm have upwards of
twenty licensees now manufacturing internal combustion engines under
their designs. This fact, though not familiar to “the man in the
street,” is known in the manufacturing world.
[Illustration: 900 B.H.P. LOW DUTY VICKERS ENGINE FOR OIL TANK VESSELS]
[Illustration: BACK VIEW OF ENGINE]
Already a very large number of their engines have been constructed,
the approximate brake horse-power produced by same being upwards of
337,600. These engines are of various sizes, ranging from 200 to 2,000
horse-power. The cylinders vary in diameter from 10 to 29 inches, and
are arranged to work in groups to suit the power required, and may be
either two-stroke or four-stroke cycle. The high temperatures set up in
starting the engine are sufficient to ignite the fuel, the introduction
of which in a finely-divided condition has been the object of so many
experiments at Barrow; and so successful in this direction have Messrs.
Vickers been that they are now able to deal satisfactorily, by careful
adjustments of the engine to suit the various fuels, with the most
troublesome oils.
As already referred to, the elimination of the air compressor
constitutes the chief improvement embodied in the Vickers type of
engine, seeing that the greatest worry which the Diesel engineer has
had to encounter has been this very compressor. Needless to remark,
therefore, this feature alone strongly recommends the new system to the
experienced man. Further, the power required to drive the compressor
above-mentioned is considerable, so that economy is not one of the
least results due to its absence.
The principal advantages that can be claimed for the Vickers engine may
be summarized as under--
1. Safety in working. (Many accidents have been due to the use
of the air compressor.)
2. Weight is saved.
3. Space is saved.
4. Lower air compression in the cylinders for ignition, and
economy in air for starting the engine.
5. Reduction in first costs; and
6. Reduction in upkeep expenses.
[Illustration: 900 B.H.P. HIGH DUTY REVERSING ENGINE FOR LIGHT CRAFT]
[Illustration: 1,250 B.H.P. LOW DUTY VICKERS MARINE ENGINE FOR OIL TANK
VESSEL]
With regard to (4), the low compression claimed is rather interesting,
as Messrs. Vickers have successfully demonstrated that, although a high
compression temperature is necessary in the ordinary Diesel engine with
the usual air spraying compressor, a much lower degree suffices for
their mechanical injection system, whilst there is a greater certainty
of ignition of the fuel on its first introduction, even with the
existence of lower compression in the cylinder. The reason of this is
that the spraying air used in the ordinary Diesel is usually compressed
to about 60 atmospheres (900 lb. per square inch). What happens when
air spraying is practised is this. When the cold air carrying the very
high pressure above mentioned enters the cylinder, it necessarily
expands, owing to the lower temperature already existent there, and
such expansion chills the whole mixture, frequently preventing ignition
on the first introduction of the fuel.
Under the Vickers system of mechanical fuel injection, there is,
of course, no introduction of very highly compressed air, and,
consequently, first ignition is rendered easier. From this, it will
at once be seen that an oil possessing a high flash point can be more
easily burned in the Vickers engine than in the ordinary Diesel, with
the necessary adjunct of an air compressor. Provision is also made
(should the type of fuel used require it) for a higher temperature of
compression, and such oils are, therefore, much more easily dealt with
than in the ordinary Diesel engine.
From what I have already said, it will be evident to the reader that it
is only a question of time for air spraying, with its attendant use of
the compressor, to become a thing of the past.
The mechanism involved by the adoption of the new system of fuel
injection developed by Messrs. Vickers is exceptionally simple. It
consists of a small fuel pump, such as is ordinarily used for pumping
fuel, a reservoir or accumulator of novel form to retain the charge,
and a valve with a special nozzle to admit the fuel in the form of a
fine spray into the cylinder. The accumulator, I may here mention,
is merely a tube, flattened slightly on the sides, and of sufficient
length, when the oil is forced into it, to enable it to yield and store
up a charge of fuel at the required high pressure, as explained in the
next paragraph.
The principal feature of the system (and the secret of its great
success) is the very high pressure at which the oil is injected into
the cylinder. This pressure is kept up at about 4,000 lb. the square
inch, so that the oil fuel, when it enters the cylinder and encounters
the hot compressed air therein, is in the form of a very finely
atomized mist, a conjunction of circumstances most favourable for
ignition. As in all great inventions, the simplicity of the arrangement
is not the least of its merits.
This somewhat rough, yet brief, outline will suffice to explain the
astonishing success of the Vickers heavy oil engine, but, if the whole
history of these (and other) noteworthy experiments could be written,
a highly interesting story would be produced, showing indomitable
perseverance in the face of discouragement, difficulty, and very heavy
expense.
I have avoided touching upon the ordinary kerosene engines, for I
imagine they are too well known to need more than passing reference
here; nor have I gone into the details concerning the advent of the
ordinary Diesel engine, which was a German invention.
I have preferred rather to deal with a British invention which is
already revolutionizing oil engine construction generally, and which,
obviously, has limitless fields open to it.