INTERNAL COMBUSTION ENGINES
OIL ENGINES--ENGINES WORKED WITH PRODUCER GAS--BLAST FURNACE GAS ENGINES
If carbon and oxygen be made to combine chemically, the process is
accompanied by the phenomenon called _heat_. If heat be applied to a
liquid or gas in a confined space it causes a violent separation of its
molecules, and power is developed.
In the case of a steam-engine the fuel is coal (carbon in a more or
less pure form), the fluid, water. By burning the fuel under a boiler,
a gas is formed which, if confined, rapidly increases the pressure on
the walls of the confining vessel. If allowed to pass into a cylinder,
the molecules of steam, struggling to get as far as possible from
one another, will do useful work on a piston connected by rods to a
revolving crank.
We here see the combustion of fuel external to the cylinder, i.e. under
the boiler, and the fuel and fluid kept apart out of actual contact.
In the gas or oil-vapour engine the fuel is brought into contact with
the fluid which does the work, mixed with it, and burnt _inside_ the
cylinder. Therefore these engines are termed _internal combustion_
engines.
Supposing that a little gunpowder were placed in a cylinder, of which
the piston had been pushed almost as far in as it would go, and that
the powder were fired by electricity. The charcoal would unite with the
oxygen contained in the saltpetre and form a large volume of gas. This
gas, being heated by the ignition, would instantaneously expand and
drive out the piston violently.
A very similar thing happens at each explosion of an internal
combustion engine. Into the cylinder is drawn a charge of gas,
containing carbon, oxygen, and hydrogen, and also a proportion of air.
This charge is squeezed by the inward movement of the piston; its
temperature is raised by the compression, and at the proper moment it
is ignited. The oxygen and carbon seize on one another and burn (or
combine), the heat being increased by the combustion of the hydrogen.
The air atoms are expanded by the heat, and work is done on the piston.
But the explosion is much gentler than in the case of gunpowder.
During recent years the internal combustion engine has been making
rapid progress, ousting steam power from many positions in which it
once reigned supreme. We see it propelling vehicles along roads and
rails, driving boats through the water, and doing duty in generating
stations and smelting works to turn dynamos or drive air-pumps--not
to mention the thousand other forms of usefulness which, were they
enumerated here, would fill several pages.
A decade ago an internal combustion engine of 100 h.p. was a wonder;
to-day single engines are built to develop 3,000 h.p., and in a few
years even this enormous capacity will doubtless be increased.
It is interesting to note that the rival systems--gas and steam--were
being experimented with at the same time by Robert Street and James
Watt respectively. While Watt applied his genius to the useful
development of the power latent in boiling water, Street, in 1794, took
out letters patent for an engine to be worked by the explosions caused
by vaporising spirits of turpentine on a hot metal surface, mixing the
vapour with air in a cylinder, exploding the mixture, and using the
explosion to move a piston. In his, and subsequent designs, the mixture
was pumped in from a separate cylinder under slight pressure. Lenoir,
in 1860, conceived the idea of making the piston _suck_ in the charge,
so abolishing the need of a separate pump; and many engines built under
his patents were long in use, though, if judged by modern standards,
they were very wasteful of fuel. Two years later Alphonse Beau de
Rochas proposed the further improvement of utilising the cylinder, not
only as a suction pump, but also as a compressor; since he saw that a
compressed mixture would ignite very much more readily than one not
under pressure. Rochas held the secret of success in his grasp, but
failed to turn it to practical account. The "Otto cycle," invented by
Dr. Otto in 1876, is really only Rochas's suggestion materialised. The
large majority of internal combustion engines employ this "cycle" of
operations, so we may state its exact meaning:--
(1) A mixture of explosive gas and air is drawn into the cylinder by
the piston as it passes outwards (i.e. in the direction of the crank),
through the inlet valve.
(2) The valve closes, and the returning piston compresses the mixture.
(3) The mixture is fired as the piston commences its second journey
outwards, and gives the "power" stroke.
(4) The piston, returning again, ejects the exploded mixture through
the outlet or exhaust valve, which began to open towards the end of the
third stroke.
Briefly stated, the "cycle" is--suction, compression, explosion,
expulsion; one impulse being given during each cycle, which occupies
two complete revolutions of the fly-wheel. Since the first, second, and
third operations all absorb energy, the wheel must be heavy enough to
store sufficient momentum during the "power" stroke to carry the piston
through all its three other duties.
Year by year, the compression of the mixture has been increased, and
improvements have been made in the methods of governing the speed
of the engine, so that it may be suitable for work in which the
"load" is constantly varying. By doubling, trebling, and quadrupling
the cylinders the drive is rendered more and more steady, and the
elasticity of a steam-engine more nearly approached.
The internal combustion engine has "arrived" so late because in the
earlier part of last century conditions were not favourable to its
development. Illuminating gas had not come into general use, and such
coal gas as was made was expensive. The great oil-fields of America and
Russia had not been discovered. But while the proper fuels for this
type of motor were absent, coal, the food of the steam-engine, lay
ready to hand, and in forms which, though useless for many purposes,
could be advantageously burnt under a boiler.
Now the situation has altered. Gas is abundant; and oil of the right
sort costs only a few pence a gallon. Inventors and manufacturers
have grasped the opportunity. To-day over 3,000,000 h.p. is developed
continuously by the internal combustion engine.
Steam would not have met so formidable a rival had not that rival had
some great advantages to offer. What are these? Well, first enter a
factory driven by steam power, and carefully note what you see. Then
visit a large gas- or oil-engine plant. You will conclude that the
latter scores on many points. There are no stokers required. No boilers
threaten possible explosions. The heat is less. The dust and dirt are
less. The space occupied by the engines is less. There is no noisome
smoke to be led away through tall and expensive chimneys. If work
is stopped for an hour or a day, there are no fires to be banked or
drawn--involving waste in either case.
Above all, the gas engine is more efficient, or, if you like to express
the same thing in other words, more economical. If you use only one
horse-power for one hour a day, it doesn't much matter whether that
horse-power-hour costs 4d. or 5d. But in a factory where a thousand
horse-power is required all day long, the extra pence make a big
total. If, therefore, the proprietor finds that a shilling's-worth of
gas or oil does a quarter as much work again as a shilling's-worth of
coal, and that either form of fuel is easily obtained, you may be sure
that, so far as economy is concerned, he will make up his mind without
difficulty as to the class of engine to be employed. A pound of coal
burnt under the best type of steam-engine gives but 10 per cent. of its
heating value in useful work. A good oil-engine gives 20-25 per cent.,
and in special types the figures are said to rise to 35-40 per cent.
We may notice another point, viz. that, while a steam-engine must be
kept as hot as possible to be efficient, an internal combustion engine
must be cooled. In the former case no advantage, beyond increased
efficiency, results. But in the latter the water passed round the
cylinders to take up the surplus heat has a value for warming the
building or for manufacturing processes.
Putting one thing with another, experts agree that the explosion engine
is the prime mover of the future. Steam has apparently been developed
almost to its limit. Its rival is but half-grown, though already a
giant.
Some internal combustion engines use petroleum as their fuel,
converting it into gas before it is mixed with air to form the charge;
others use coal-gas drawn from the lighting mains; "poor gas" made in
special plants for power purposes; or natural gas issuing from the
ground. Natural gas occurs in very large quantities in the United
States, where it is conveyed through pipes under pressure for hundreds
of miles, and distributed among factories and houses for driving
machinery, heating, and cooking. In England and Europe the petroleum
engine and coal-gas engine have been most utilised; but of late the
employment of smelting-furnace gases--formerly blown into the air
and wasted--and of "producer" gas has come into great favour with
manufacturers. The latest development is the "suction" gas engine,
which makes its own gas by drawing steam and air through glowing fuel
during the suction stroke.
We will consider the various types under separate headings devoted
(1) To the oil-fuel engine,
(2) The producer-gas engine and the suction-gas engine,
(3) Blast-furnace gas engines, with reference to the installations used
in connection with the last two.
All explosion engines (excepting the very small types employed on motor
cycles) have a water-jacket round the cylinders to absorb some of the
heat of combustion, which would otherwise render the metal so hot as to
make proper lubrication impossible, and also would unduly expand the
incoming charge of gas and air before compression. The ideal engine
would take in a full charge of cold mixture, which would receive no
heat from the walls of the cylinder, and during the explosion would
pass no heat through the walls. In other words, the ideal metal for the
cylinders would be one absolutely non-receptive of heat. In the absence
of this, engineers are obliged to make a compromise, and to keep the
cylinder at such a temperature that it can be lubricated fittingly,
while not becoming so cold as to absorb _too much_ of the heat of
explosion.
OIL ENGINES
These fall into two main classes:--
(a) Those using light, volatile, mineral oils--such as petrol and
benzoline--and alcohol, a vegetable product.
(b) Those using heavy oils, such as paraffin oil (kerosene) and the
denser constituents of rock-oil left in the stills after the kerosene
has been driven off. American petroleum is rich in burning-oil and
petrol; Russian in the very heavy residue, called _astakti_. Given the
proper apparatus for vaporisation, mineral oils of any density can be
used in the explosion engine.
The first class is so well known as the mover of motor vehicles and
boats that we need not linger here on it. It may, however, be remarked
that engines using the easily-vaporised oils are not of large powers,
since the fuel is too expensive to make them valuable for installations
where large units of power are needed. They have been adopted for
locomotives on account of their lightness, and the ease with which they
can be started. Petrol vaporises at ordinary temperatures, so that air
merely passed over the spirit absorbs sufficient vapour to form an
explosive mixture. The "jet" carburetter, now generally employed, makes
the mixture more positive by atomising the spirit as it passes through
a very fine nozzle into the mixing chamber under the suction from the
cylinder. On account of their small size spirit engines work at very
high speeds as compared with the large oil or gas engine. Thus, while
a 2,000 h.p. Körting gas engine develops full power at eighty-five
revolutions a minute, the tiny cycle motor must be driven at 2,000 to
3,000 revolutions. Speaking generally, as the size increases the speed
decreases.
Of heavy oil engines there are some dozens of well-tried types. They
differ in their methods of effecting the following operations.
1. The feeding of the oil fuel to the engine.
2. The conversion of the oil into vapour.
3. The ignition of the charge.
4. The governing of speed.
All these engines have a vaporiser, or chamber wherein the oil is
converted into gas by the action of heat. When starting-up the engine,
this chamber must be heated by a specially designed lamp, similar in
principle to that used by house painters for burning old paint off wood
or metal.
Let us now consider the operations enumerated above in some detail.
1. _The oil supply._ Fuel is transferred from the storage tank to the
vaporiser either by the action of gravity through a regulating device
to prevent "flooding," or by means of a small pump, or by the suction
of the piston, which _lifts_ the liquid. In some engines the air and
gas enter the cylinder through a single valve; in others through
separate valves.
2. _Vaporisation._ As already remarked, the vaporising chamber must be
heated to start the engine. When work has begun the lamp may be removed
if the engine is so designed that the chamber stores up sufficient heat
in its walls from each explosion to vaporise the charge for the next
power stroke. The Crossley engine has a lamp continuously burning; the
Hornsby-Ackroyd depends upon the storage of heat from explosions in a
chamber opening into the cylinder. The best designs are fairly equally
divided between the two systems.
3. _Ignition_ of the compressed charge is effected in one of four ways:
by bringing the charge, at the end of the compression stroke, into
contact with a closed tube projecting from the cylinder and heated
outside by a continuously burning lamp; by the heat stored in some
part of the combustion chamber (_i.e._ that portion of the cylinder
not swept by the piston); by an electric spark; or by the mere heat of
compression. The second and third methods are confined to comparatively
few makes; and the Diesel Oil Engine (of which more presently) has a
monopoly of the fourth.
4. _Governing._ All engines which turn machinery doing intermittent
work--such as that of a sawmill, or electric generating plant
connected with a number of motors--must be very carefully guarded from
overrunning. Imagine the effect on an engine which is putting out its
whole strength and getting full charges of fuel, if the belt suddenly
slipped off and it were "allowed its head." A burst fly-wheel would be
only one of the results. The steam-engine is easily controlled by the
centrifugal action of a ball-governor, which, as the speed increases,
gradually spreads its balls and lifts a lever connected with a valve
in the steam supply pipe. Owing to its elastic nature, steam will do
useful work if admitted in small quantities to the cylinder. But a
difficulty arises with the internal combustion engine if the _supply_
of mixture is similarly throttled, because a loss of quantity means
loss of compression and bad ignition. Many oil engines are therefore
governed by apparatus which, when the speed exceeds a certain limit,
cuts off the supply altogether, either by throwing the oil-pump
temporarily out of action, or by lifting the exhaust valve so that the
movement of the piston causes no suction--the "hit-and-miss" method, as
it is called.
The means adopted depends on the design of the engine; and it must
be said that, though all the devices commonly used effect their
purpose, none are perfect; this being due rather to the nature of an
internal explosion engine than to any lack of ingenuity on the part of
inventors. The steadiest running is probably given with the throttle
control, which diminishes the supply. On motor cars this method has
practically ousted the "hit-and-miss" governed exhaust valve; but
in stationary engines we more commonly find the speed controlled by
robbing the mixture of the explosive gas in inverse proportion to the
amount of the work required from the engine.
THE DIESEL OIL ENGINE,
on account of some features peculiar to it, is treated separately.
In 1901 an expert wrote of it that "the engine has not attained any
commercial position." Herr Rudolph Diesel, the inventor, has, however,
won a high place for his prime-mover among those which consume liquid
fuel, on account of its extraordinary economy. The makers claim--as the
result of many tests--that with the crude rock-oil (costing in bulk
about 2d. a gallon) which it uses, a horse-power can be developed for
one hour by this engine for _one-tenth of a penny_. The daily fuel bill
for a 100 h.p. engine running ten hours per day would therefore be 8s.
4d. To compete with the Diesel engine a steam installation would have
to be of the very highest class of triple-expansion type, of not less
than 400 h.p., and using every hour per horse-power only 1-3/4 lbs. of
coal at 9s. per ton. Very few large steam-engines work under conditions
so favourable, and with small sizes 3-4 lbs. of coal would be burnt for
every "horse-power-hour."
The Diesel differs from other internal combustion engines in the
following respects:--
1. It works with very much higher compression.
2. The ignition is spontaneous, resulting from the high
compression of the charge alone.
3. The fuel is not admitted into the cylinder until the
power-stroke begins, and enters in the form of a
fine spray.
4. The combustion of the fuel is much slower, and therefore
gives a more continuous and elastic push to the
piston.
The engine works on the ordinary Otto cycle. To start it, air
compressed in a separate vessel is injected into the cylinder. The
piston flies out, and on its return squeezes the air to about 500 lbs.
to the square inch, thus rendering it incandescent.[11] Just as the
piston begins to move out again a valve in the cylinder-head opens, and
a jet of pulverised oil is squirted in by air compressed to 100 lbs.
per square inch more than the pressure in the cylinder. The vapour,
meeting the hot air, burns, but comparatively slowly: the pressure in
the cylinder during the stroke decreasing much more gradually than in
other engines. Governing is effected by regulation of the amount of oil
admitted into the cylinder.
In spite of its high compression this engine runs with very little
vibration. The writer saw a penny stand unmoved on its edge on the top
of a cylinder in which the piston was reciprocating 500 times a minute!
ENGINES WORKED BY PRODUCER-GAS
These engines are worked by a special gas generated in an apparatus
called a "producer." If air is forced through incandescent carbon in
a closed furnace its oxygen unites with the carbon and forms carbonic
acid gas, known chemically as CO_{2}, because every molecule of the
gas contains one atom of carbon and two of oxygen. This gas, being
the product of combustion, cannot burn (_i.e._ combine with more
oxygen), but as it passes up through the glowing coke, coal, or other
fuel, it absorbs another carbon atom into every molecule, and we have
C_{2}O_{2}, or 2 CO, which we know as _carbon monoxide_. This gas may
be seen burning on the top of an open fire with a very pale blue flame,
as it once more combines with oxygen to form carbonic acid gas.
The carbon monoxide is valuable as a heating agent, and when mixed with
air forms an explosive mixture.
If along with the air sent into our furnace there goes a proportion
of steam, further chemical action results. The oxygen of the steam
combines with carbon to form carbon monoxide, and sets free the
hydrogen. The latter gas, when it combines with oxygen in combustion,
causes intense heat; so that if from the furnace we can draw off carbon
monoxide and hydrogen, we shall be able to get a mixture which during
combustion will set up great heat in the cylinder of an engine.
In 1878 Mr. Emerson Dowson invented an apparatus for manufacturing
a gas suitable for power plant, the gas being known as Producer or
Poor Gas, the last term referring to its poorness in hydrogen as
compared with coal and other gases. While the hydrogen is a desirable
ingredient in an explosive charge, it must not form a large proportion,
since under compression it renders the mixture in which it takes part
dangerously combustible, and liable to spontaneous ignition before the
piston has finished the compression stroke. Water-gas, very rich in
hydrogen, and made by a very similar process, is therefore not suitable
for internal combustion engines.
There are many types of producers, but they fall under two main heads,
_i.e._ the _pressure_ and the _suction_.
The _pressure_ producer contains the following essential parts:--
The _generator_, a vertical furnace fed from the top through an
air-tight trap, and shut off below from the outside atmosphere by
having its foot immersed in water. Any fuel or ashes which fall through
the bars into the water can be abstracted without spoiling the draught.
Air and steam are forced into the generator, and pass up through the
fuel with the chemical results already described. The gases then flow
into a _cooler_, enclosed in a water-jacket, through which water
circulates, and on into a _scrubber_, where they must find their way
upwards through coke kept dripping with water from overhead jets. The
water collects impurities of all sorts, and the gas is then ready for
storage in the gas-holders or for immediate use in the engines.
A pound of anthracite coal thus burnt will yield enough gas to develop
1 h.p. for one hour.
_Suction Gas Plants._--With these gas is not stored in larger
quantities than are needed for the immediate work of the engine. In
fact, the engine itself during its suction strokes _draws_ air and
steam through a very small furnace, coolers, and scrubbers direct into
the cylinder. The furnace is therefore fed with air and water, not
by pressure from outside, but by suction from inside, hence the name
"suction producer." At the present time suction gas engines are being
built for use on ships, since a pound of fuel thus consumed will drive
a vessel further than if burnt under a steam boiler. Very possibly the
big ocean liners of twenty years hence may be fitted with such engines
in the place of the triple and quadruple expansion steam machinery now
doing the work.
BLAST-FURNACE GAS ENGINES
Every iron blast-furnace is very similar in construction and action
to the generator of a producer-gas plant. Into it are fed through
a hopper, situated in the top, layers of ore, coal or coke, and
limestone. At the bottom enters a blast of air heated by passing
through a stove of firebrick raised to a high temperature by the carbon
monoxide gas coming off from the furnace. When the stove has been
well heated the gas supply is shut off from it and switched to the
engine-house to create power for driving the huge blowers.
The gas contains practically no hydrogen, as the air sent through
the furnace is dry; but since it will stand high compression, it is
very suitable for use in large engines. Formerly all the gas from the
furnace was expelled into the open air and absolutely wasted; then
it was utilised to heat the forced draught to the furnace; next, to
burn under boilers; and last of all, at the suggestion of Mr. B. H.
Thwaite, to operate internal combustion engines for blowing purposes.
Thus, in the fitness of things, we now see the biggest gas engines in
the world installed where gas is created in the largest quantities, and
an interesting cycle of actions results. The engine pumps the air; the
air blows the furnace and melts the iron out of the ore; the furnace
creates the gas; the gas heats the air or works the engines to pump
more air. So engines and furnace mutually help each other, instead of
all the obligation being on the one side.
When, a few years ago, the method was first introduced, engines were
damaged by the presence of dust carried with the gas from the furnace.
Mr. B. H. Thwaite has, however, perfected means for the separation of
injurious matter, and blast-furnace gas is coming into general use in
England and on the Continent. Some idea of the power which has been
going to waste in ironworks for decades past may be gathered from a
report of Professor Hubert after experiments made in 1900. He says that
engines of large size do not use more than 100 cubic feet of average
blast-furnace gas per effective horse-power-hour, which is less than
one-fourth of the consumption of gas required to develop the same power
from boilers and good modern condensing steam-engines, so that there
is an immense surplus of power to be obtained from a blast-furnace
if the blowing engines are worked by the gas it generates, a surplus
which can be still further increased if the gas is properly cleaned.
It is estimated that for every 100 tons of coke used in an ordinary
Cleveland blast-furnace, after making ample allowance for gas for the
stoves and power for the lifts, pumps, etc., and for gas for working
the necessary blowing engines, there is a surplus of at least _1,500
h.p._; so that by economising gas by cleaning, and developing the
necessary power by gas engines, every furnace owner would have a very
large surplus of power for his steel or other works, or for selling in
the form of electricity or otherwise.
Yet all this gas had been formerly turned loose for the breezes to warm
their fingers at! Truly, as an observant writer has recorded, the sight
of a special plant being put up near a blast furnace to manufacture gas
for the blowing engines suggests the pumping of water uphill in order
to get water-power!
Messrs. Westgarth and Richardson, of Middlesbrough; the John Cockerill
Company, of Seraing, Belgium; and the De la Vergne Company, of New
York, are among the chief makers of the largest gas engines in the
world, ranging up to 3,750 h.p. each. These immense machines, some with
fly-wheels 30 feet in diameter, and cylinders spacious enough for a man
to stand erect in, work blowers for furnaces or drive dynamos. At the
works of the manufacturers mentioned the engines helped to make the
steel, and turn the machinery for the creation of brother monsters.
[Illustration: GIGANTIC GAS ENGINES
Five of sixteen 2,000 h.p. Körting Gas Engines built by the De la
Vergne Company of New York City for blowing the blast furnaces of the
Lackawanna Steel Company. The gas-engine plant at these works is the
largest in the world. Notice the man to the left.]
This use of a "bye-product" of industry is remarkable, but it can be
paralleled. Furnace slag, once cast away as useless, is now recognised
to be a valuable manure, or is converted into bricks, tiles, cement,
and other building materials. Again, the former waste from the coal-gas
purifier assumes importance as the origin of aniline dyes, creosote,
saccharine, ammonia, and oils. We really appear to be within sight of
the happy time when waste will be unknown. And it therefore is curious
that we still burn gas as an illuminant, when the same, if made to work
an engine, would give more lighting power in the shape of electric
current supplying incandescent lamps.
FOOTNOTE:
[11] The fact that air is heated to combustion point by compression has
long been known to the Chinese. In _The River of Golden Sand_, Captain
Gill writes: "The natives have an apparatus by which they strike a
light by compressed air. The apparatus consists of a wooden cylinder
2-1/2 inches long by 3/4 inch in diameter. This is closed at one end;
the bore being about the size of a stout quill pen, an air-tight piston
fits into this with a large flat knob at the top. The other end of the
piston is slightly hollowed out, and a very small piece of tinder is
placed on the top thus formed. The cylinder is held in one hand, the
piston inserted and pushed about half-way down; a very sharp blow is
then delivered with the palm of the hand on to the top of the knob; the
hand must at the same time close on the knob, and instantly withdraw
the piston, when the tinder will be found alight. The compression of
the air produces heat enough to light the tinder; but this will go out
again unless the piston is withdrawn very sharply. I tried a great many
times, but covered myself with confusion in fruitless efforts to get a
light, for the natives never miss it."