But these results did not suffice, and it was desired to do better still
by dispensing with the use of high priced illuminating gas. An endeavor
was made to obviate the difficulty by manufacturing a special gas for
the motive power, as steam is produced for the same object, by
distilling coal, carbureting air, producing water gas by the Dowson
process, and by other equivalent processes.
The strides made in this direction were finally crowned with success,
and the results obtained in the recent experiments due to Mr. Aimé Witz,
an undoubted authority in the matter, permit of affirming that now and
hereafter, in many circumstances, a gas generator supplying a gas motor
will be able to advantageously dethrone a steam boiler supplying a steam
engine of the same power.
These conclusions, which tend to nothing less than to limit the reign of
the steam engine, are confirmed on the one hand by an experiment carried
on for the last two years in the Barataud flour mill of Marseilles,
where a 50 h.p. "Simplex" motor has been running day and night for
several months without stopping, and consuming but about 500 grammes of
English anthracite per effective horse hour, and, on another hand, by
some personal experiments of Mr. Witz's, to which we shall shortly
advert, and whence there results a sensibly equivalent production for a
motor of 100 indicated h.p., corresponding to a power of 75 effective
horses.
Before establishing, with Mr. Witz, a comparison of the two systems in
pressure, steam or gas, let us state in a few words in what the latter
consists, the steam engine and the boiler that supplies it being so well
known that no description is necessary.
The Dowson gas generator does not differ essentially from the numerous
generators devised during recent years for the manufacture of gaseous
combustibles, the use of which is so often convenient. The motor that it
supplies is the most powerful single cylinder one that has hitherto been
constructed. It is of 100 indicated h.p., and its normal angular
velocity is 100 revolutions per minute. On trial it has yielded 112
indicated h.p., and 76.8 effective h.p., corresponding to an organic
rendering of 69 per cent. This motor, elaborated by Messrs.
Delamare-Bouteville & Malandin, of Rouen, operates by compression and in
four periods, according to the Beau de Rochas cycle. We give the aspect
of it in Fig. 3. In the first period the mixture of air and gas is
sucked in, in the second it is compressed, in the third it is ignited,
and in the fourth the products of combustion are expelled.
[Illustration: FIG. 2.--SIMPLEX MOTOR, DOWSON GENERATOR OF 100 INDICATED
H.P.--ELEVATION AND PLAN.
A, cylinder; B, gas conduit; C, rubber pockets; D. gasometer; E,
purifier; F, scrubber; G, hydraulic main; H, cooling pipe; I steam
injector; K, steam boiler and superheater; L, gas generator; M, charger;
N, discharge of the motor.]
Ignition is effected electrically by a series of sparks playing between
two platinum points in the slide valve, and this permits of regulating
the instant of ignition through the edges of the orifices. The angular
velocity is regulated by a Watt's governor, which secures an isochronism
of the motion independently of the charge.
The setting in motion of so powerful an engine is effected very easily
by means of an arrangement that permits of introducing into the
cylinder, while the piston is in the center of the stroke, a mixture of
air and gas whose pressure is sufficient at the arrival to expel the
inert products. After this the ignition takes place, and the explosion
is sufficient to set the motor in motion.
The trials made by Mr. Witz with the motor represented in Fig. 3 gave
the following results, deduced from an experiment of 68 hours. The
figures relate to one effective horse power, measured with the brake
upon the shaft of the motor.
Consumption of anthracite. 516 grammes.
" " coke. 96 "
Consumption of water for the injection
of steam. 0.487 liters.
Consumption of water for cooling
the cylinder. 50.0 "
Consumption of oil for lubricating
the cylinder. 3.74 grammes.
Consumption of grease. 0.45 "
Consumption of gas reduced to
0° C. and to 760 mm. 2,370 liters.
This last figure will appear very high, but the fact must not be lost
sight of that it is a question of poor gas, the net cost of which varies
between one and two centimes per cubic meter, and the calorific power of
which is but 1,487 heat units per cubic meter of constant volume, and
supposing the steam condensed. This combustion of 612 grammes of
combustible per effective horse hour is remarkable, and fully shows what
may be expected of the gas motor supplied by a gas generator in putting
to profit certain improvements that will hereafter be possible, such,
for example, as the lightening of the movable parts of the motor, the
bettering of its organic rendering (now quite feeble), the use of better
oils, the reduction of the consumption of water, the superheating of the
steam injected into the gas generator, etc.
A well constructed steam engine, carefully kept in repair and as much
improved as it is possible to make it, would certainly consume twice as
much coal to produce the same quantity of effective work, say at least
1,200 grammes per horse hour. But, as has been objected with reason, it
does not suffice to compare the figures as to the consumption of fuel in
order to institute a serious comparison between the steam engine and the
motor using poor gas.
The gas generator requires the use of English anthracite, while a steam
boiler is heated with any kind of coal. The prices of unity of weight
are therefore very different. Moreover, the gas motor necessitates an
immense amount of water for the washing of the gas and the cooling of
the cylinder, through circulation in the jacket. It is well to keep this
fact in view. On another hand, the lubrification of the cylinders
requires a profusion of oil whose flashing point must be at a very high
temperature, else it would burn at every explosion and fill the cylinder
with coom. Such oil is very costly.
Does not the expenditure of oil in large motors largely offset the
saving in coal? And then, gas motors are sold at high prices, as are gas
generators, and this installation necessarily requires the addition of a
large gasometer, scrubbers, etc. The wear of these apparatus is rapid,
and if we take into account the interest and amortization of the capital
engaged, we shall find that the use of steam is still more economical.
The obstruction caused by bulky apparatus is another inconvenience, upon
which it is unnecessary to dwell. In a word, the question is a very
complex one. We look at but one side of it in occupying ourselves only
with the coal consumed, and we shall certainly expose those who allowed
themselves to be influenced by the seductive figures of consumption to
bitter disappointment.
To answer such objections Mr. Aimé Witz has established a complete
parallel between the two systems, in which he looks at the question from
a theoretical and practical and scientific and financial point of view.
Considered as a transformation apparatus, a steam motor burning good
Cardiff coal in a Galloway boiler with feed water heaters will consume
(with a good condensing engine utilizing an expansion of a sixth) from
1,100 to 1,250 grammes of coal per effective horse hour, which
corresponds to a rough coefficient of utilization of 9.7 per cent. A gas
generator supplying a gas motor burning Swansea anthracite and Noeux
coke, medium quality, will consume 516 grammes of anthracite and 90 of
coke to produce 2,370 liters of gas giving 1,487 heat units per cubic
meter. Of the 3,524 heat units furnished to the motor by the 2,370
liters of gas, the motor will convert 18 per cent. into disposable
mechanical work.
With the boiler, the gross rendering of the whole is 7 per cent. With
the gas generator it reaches 12.7 per cent. From a theoretical point of
view the advantage therefore rests with the gas generator and gas motor.
In order to compare the net cost of the units of work, from an
industrial point of view, it is necessary to form estimates of
installation, costs of keeping in repair, interest and amortization.
Figs. 1 and 2 represent, on the same scale, the installations necessary
in each of these systems. The legends indicate the names of the
different apparatus in each installation. The following table shows
that, as regards the surface occupied, the advantage is again with the
gas generator and gas motor:
Steam Engine. Gas Motor.
Surface covered. 85 sq. m. 72 sq. m.
Surface exposed. 33 " 43 "
--- ---
Total surface. 118 " 115 "
The estimates of installation formed by Mr. Witz set forth the expense
relative to the capital engaged exactly at the same figure of 32,000
francs for a motive power of 75 effective horses. The expenses of
keeping in repair, interest, etc., summed up, show that the cost per day
of 10 hours is 47.9 francs for the steam engine and 39.6 for the gas
motor, say a saving of 8.3 francs per day, or about 2,500 francs for a
year of 300 days' work.
The gas motor, therefore, effects a great saving, while at the same time
occupying less space, consuming less water and operating just as well.
With Mr. Witz we cheerfully admit all the advantages that he so clearly
establishes with his perfect competency in such matters, but there still
remain two points upon which we wish to be enlightened. Are not the
starting up, the operation and the keeping in repair of a gas generator
actually more complicated and more delicate than the same elements of a
steam engine? Does not the poor gas manufactured in a gas generator
present, from a hygienic point of view, danger sufficiently great to
proscribe the use of such apparatus in many circumstances?
Such are the points upon which we should like to be enlightened before
unreservedly sharing Mr. Witz's enthusiasm, which, however, is
justified, economically speaking, by the magnificent results of the
experiments made by the learned engineer.--_La Nature_.
[Illustration: FIG. 3.--GAS MOTOR OF 100 INDICATED HORSE POWER.]
* * * * *