M. Witz, says the _Gas World_, has been conducting a series of
experiments on the Delamare-Deboutteville and Malindin gas engine,
driven by Dowson gas, and in which the gas generator takes the place of
the ordinary steam boiler. The engine was a one-cylinder motor in the
establishment of Messrs. Matter & Co., Rouen. Its power was 100 horse
indicated; the cylinder was 23 inches in diameter, the stroke 38 inches,
and the normal speed 100 revolutions. The engine is of the Simplex type;
the kindling is electric; the cycle of operations is fourfold, with
powerful compression. The Dowson generator is 30 inches inside diameter
and 76 inches in height from the bars to the top. Air is blown in by
steam driven in under the hearth. There is a siphon, a coke scrubber 110
inches high, a sawdust purifier, and a gasholder of 750 cubic feet
capacity, and a pipe to the engine 5.2 inches in diameter. The total
area occupied by this apparatus is 140 square yards, of which two-thirds
are built on. The anthracite employed was from Swansea, containing 5.4
per cent. of ash. The observations made with a string friction brake
were continued for 68 hours, everything used being carefully weighed and
measured. One day the machine was worked for 15¼ hours on end; the other
days it was worked with an interval of half an hour every 12 hours to
clear the hearth, poke the fire and lubricate the machine; and it was
clearly established that with a big enough generator it would be quite
possible to work continuously for several days.
The following were the data for a day of 24 hours, with an interval of
half an hour: 8:55 P.M. one day to 8:55 P.M. the next, interval 8:30 to
9 A.M. Anthracite used, 18.4 cwt.; coke used, 3.42 cwt.; water used for
steam injection, 217.3 gallons; water used in scrubber, 4,106 gallons;
water used in cooling the cylinder, 20,000 gallons; oil used in
cylinder, 14.84 pounds; grease, 1.8 pounds; revolutions of machine,
142,157, or 100.8 per minute; effective work, 75.86 French horse power,
or 77.4 British; gas used, 6,742 cubic feet per hour, at 772 mm.
pressure and 70.7° F., or 83.7 cubic feet per effective horse power;
efficiency, 69 per cent.
Now, with regard to the comparison between the large gas motors and
steam engines of the same size, M. Witz goes on to remark that the gas
engine is by no means, as was formerly thought on high authority,
necessarily restricted to the domain of smaller work and sizes. Even in
early times it was seen that the gas engine belonged to a type in which
there were possibilities of improvement greater than those available in
the steam engine, because the difference of temperature between the
working substance in its hotter and its cooler condition was greater
than in the steam engine; and consumptions of 5,250 cubic feet per horse
power per hour soon descended step by step as far as 2,060, while the
power went up, past 4, 8 and 12, to 25 or 50 horse power; and in the
exhibition of 1889 there were gas engines seen in which the explosion
chamber had a diameter of as much as 23 inches.
But the price of coal gas seemed to be too high for use in these large
engines, in which sizes steam is comparatively cheap; and so poorer gas,
which, though possessing only about 28 per cent. of the heating power,
is still cheaper in proportion than coal gas, when it is made on the
spot, was introduced to tide over the difficulty. Difficulties have been
successively overcome, with the result which we have just seen, namely,
1.37 pounds of anthracite per effective horse power, or about half the
carbon which a steam engine of the same power of excellent design, and
well kept up, would consume. A 50 horse simplex at Marseilles, in
Barataud's flour mill, is said to have run for the last 2 years on 1.12
pounds of English anthracite per effective horse power; and thus M. Witz
says his predictions of 10 years ago, that the gas producer would some
day replace the boiler, are being verified in such a way as to surprise
even himself.
But the objection is stated, and it is a serious one: the weight of fuel
is not the only thing to be considered. The steam engine uses coal, the
producer requires English anthracite, which is dearer; the gas motor
uses a great deal of water and a great deal of oil, which cost money;
and gas motors are dear, while gas producers and their adjuncts cost a
tidy bit of money, and wear out pretty fast. Is not steam, after all,
more economical in the long run? Besides, producers are bulky and take
up a great deal of space; the weight of fuel is only one element in a
complicated problem.
In order to study the grounds of this objection, M. Witz has instituted
a comparison between the actual cost of large steam engines and that of
gas motors of similar size.
Take a good Galloway or multitubular boiler; for 75 horse power
effective the heating surface must be at least 74 square feet. Using
good Cardiff coal, with 4 per cent. of ash, and a heating power of
15,660 Fahr. units; the steam raised will be 8 to 9 pounds per pound of
coal, so that 9,400 to 10,577 Fahr. units are utilized in raising steam,
or 68 to 76 per cent., which is an excellent result. Take an engine of
16 inch cylinder diameter, 40 inch stroke, and 66 revolutions, etc.; it
will use 22.4 pounds of steam per horse power effective, which
represents 2.47 to 2.8 pounds of coal under the boiler. These 10 pounds
of steam carry 11,752 Fahr. units of heat, and produce work equal to 75
horse, or 1,143 Fahr. units of heat; which corresponds to an efficiency
of 9.7 per cent. In a gas motor, on the other hand, we find the
materials employed, as per the above data, to contain 8,958 Fahr. units
of heat, and to make gaseous fuel in which 6,343 units are available; a
return of 70.6 per cent, in the producer. The motor receives these
6,343, and converts 1,143 of them into work; an efficiency of 18 per
cent. In order to be equivalent from the heat point of view, a steam
engine ought to produce a horse power effective per 9.72 pounds of steam
at 5 atmospheres; but no such steam engine exists.
M. Witz goes on with comparative estimates. For a Corliss engine and
boiler, with chimney, etc., complete, and putting these up, he allows
£1,280; for a Simplex gas motor and Dowson producer complete, including
putting up, he allows £1,290, which he explains to be average actual
prices; but these prices do not cover cost of transport, and M. Witz
does not go into cost of masonry for buildings, apart from foundations,
etc., for the apparatus and machinery.
As to water, the gas motor takes 215 cubic feet per horse power
effective. A condensing steam engine uses five times as much.
The lubricating oil used at Rouen was a mixture of Russian oil at 430
fr. per ton, and Ferry and Heduit F.H. oil at 900 fr.; the average was
650 fr. per ton, or 2.8d. per pound. Wanner grease, at 6.4d. per pound,
was used for the moving parts. A steam engine requires less oil for the
cylinder, but the same quantity for the moving parts.
The attendance on the gas motor is too much for one man, not enough to
occupy two; reckon it at 4s. 9½d. a day.
These elements enable us to calculate the daily cost of the gas motor,
of 75 actual horse power, in comparison with a steam engine of the same
size.
_Steam Engine_.
s. d.
Upkeep, interest and sinking fund at 15 per
cent, on £1,292 = £193.8 = per day. 12 11
Cardiff coal, 2.643 pounds per actual horse
power per hour; 2.643 × 10 × 75 = in 10
hours 1,982 pounds coal at 22s. a ton. 19 5½
Oil, 3.36 pounds per day at 2.8d. per pound. 0 9½
Grease, 0.67 pound at 6.4d. 0 4½
Wages. 4 9½
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£1 18 4
_Gas Engine_.
s. d.
Upkeep, interest and sinking fund at 15 per
cent. on £1,292 is, per day. 12 11
Anthracite, 1.156 pound per actual horse
power per hour = for 750 horse-hours, at
25s. 6d. 9 10
Coke, 0.215 pound × 10 × 75 = 161¼ pounds
at 28s. 2 0
Oil, 0.0084 pound per actual horse power per
hour, or 0.0084 × 10 × 75 = 6.28 pounds at
2.8d. 1 5½
Grease, 0.754 pound per day at 6.4d. 0 5
Electric kindling, on cost. 0 3½
Wages. 4 9½
---------
£1 11 8
The big gas engine making its own poor gas, and running 10 hours a day,
has thus the best of it in the comparison with the steam engine of equal
power.
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