[This
encyclopedia article was originally written about George Brayton's
engine in 1875, three years after he was issued a patent for it.
Brayton had previously worked improving steam engines, for which he
held an earlier patent. The illustration shows a marked resemblance to
a steam engine with its rocking beam and flywheel. Notice that his
engine needed no spark plug - it had a continuously burning flame to
ignite each cycle of the engine. The article reveals that for a few
years, Brayton's engine was well regarded, but within a short time
the Otto engine became more popular.]
Gas Engine
Extract from Johnson's (revised) Universal
Cyclopaedia (1886)
Fig. 1.
Brayton's High-Pressure Gas Engine
Fig. 2.
Section of Brayton's Gas Engine: induction chamber enlarged
...A very different judgement must be
pronounced upon an an American
invention patented by George B. Brayton Apr. 2, 1872, and known as
Brayton's Ready Motor, in which petroleum is the fuel ordinarily used,
though it was originally designed for gas. This engine employs, like
those already described, a mixture of gas or vapor with atmospheric air
in explosive proportions - say one part of the former to twelve of the
latter - but, unlike the others, it burns this mixture in the cylinder
without explosion, and expends upon the piston the energy derived from
its combustion with the same steady pressure as that exerted by
steam-engine or by rarefied air in the hot-air engine. This remarkable
effect is produced by the simple expedient of delivering the gaseous
mixture into the cylinder through the meshes of a separating sheet of
wire-gauze, and inflaming the mixture on the surface of the gauze next
to the cylinder. The same phenomenon occurs here which is seen in
Davy's safety lamp. When the lamp is lighted and immersed in an
explosive mixture, the gas which passes through the meshes of the
wire-gauze cap burns quietly in the interior, so that the whole cap
seems to be full of flame; but the gauze effectually prevents this
flame from reaching and igniting the mixture outside. So in this
engine, the flame is confined to the cylinder and is prevented by the
wire-gauze from running back through the passages and exploding the
mixture in the reservoir. For greater security, two or three successive
screens are introduced.
As this engine is evidently destined to
occupy
a very important place in many industries, it seems to deserve a more
particular description than we have given to those previously
mentioned. Fig. 1 presents a perspective elevation showing the
cylinder, working beam, fly-wheel, and driving-pulley with certain
pipes the purpose of which will be better understood from Figure 2.
This figure shows a section of the cylinder, piston and valves of which
there are four. As the engine is only single-acting, the upper valves a
and b may for the moment be disregarded. The induction valve is a, and
the exhaust valve v. The valve a admits the combustible mixture to
enter by the pipe S through the shallow chamber H, in which are placed
the wire-gauze diaphragms k, k, into the cylinder beneath the piston.
Through the valve-seat there is made a small perforation which may be
closed more or less nearly by the pointed screw c. The pipe S is that
which, in Fig. 1 carries the screw-valve between the cylinder and a
reservoir within the fluted column, in which a certain quantity of the
combustible mixture is contained under pressure. When the screw-valve
is opened, the gas, entering through S, makes its way by the small
aperture in the valve-seat at c into the shallow chamber H. When it is
desired to set the engine in motion, the piston is brought near the
bottom of the cylinder by turning the fly-wheel, and a lighted match is
introduced from without into the chamber H by an aperture not shown,
which is then closed. The gas in H takes fire, and as the supply is
continuous it continues to burn. The fly-wheel is then turned a little
further so as to open the induction-valve, when the engine immediately
begins to operate. Its motion can only be arrested by cutting off the
supply by means of the screw-valve.
We will now give attention to the valves
at the top of the cylinder.
The left-hand valve communicates with a gasometer which itself supplies
through two inlets - one introducing atmospheric air and the other
inflammable gas, in the proportion of twelve to one. As the piston
descends, the cylinder behind it is filled through a with this
explosive mixture. As it reascends, the valve a closes and b opens, the
charge in A being forced through this into the reservoir from which the
supply of the cylinder is drawn. The upper part of the cylinder is
somewhat enlarged, so that when the piston is at its highest point,
there still remains in it a quantity of gas equal to about one charge.
It is easily seen that, if the cut-off is placed low, the volume of gas
admitted at each stroke will be proportionally less than that driven
into the reservoir; but as it is also obvious that, after running a
short time, the mass of gas drawn out in a given time, must be exactly
equal to that forced in the same time, the pressure under which the
engine works may be increased by shortening the cut-off, or by
diminishing the length of it.
To prepare the engine to start, it is
obvious that a certain pressure
must first be got up to the reservoir. This need be only sufficient to
set the engine running. After it has once started it will regulate
itself, and will soon create the pressure due to the length of the
cut-off. In small engines, this preliminary pressure may be got up by a
few turns of the fly-wheel. For large ones a force-pump must be used;
but once got up, there is no need that it should be run down. If the
valves are close, even in long intervals of repose. As the reservoir
has the capacity of only three or four charges, it is not great labor
to prepare it.
The efficiency of this engine is due to
the expansion of the air
introduced, and of the products of combustion (carbonic acid and steam)
by the heat generated in the same combustion. The pressure in the
cylinder is no greater than that in the reservoir. The opposing
pressure is at first only that of the atmosphere, but rises toward the
end of the stroke to be equal to that in the reservoir. The action of
the engine therefore in every respect resembles that of a hot-air
engine; and it is to this class, rather than to the class of
gas-engines, that it properly belongs. Though hot-air engines are in
theory the most economical of engines driven by heat, the economy of
theory has never been realized from them in practice, in consequence of
the extreme difficulty of imparting heat to the air. Radiant heat in
this case produces but little effect: and to heat air thoroughly by
contact requires a complicated construction which seriously impedes
circulation and increases the resistance of friction. The Brayton motor
has practically resolved this difficulty, by mingling the fuel with the
air itself, so that the whole heat of combustion is imparted to the air
directly. It is therefore a hot-air engine without a furnace, or one in
which the furnace is the cylinder.
When the economical performance of this
engine was tested, it was found
that the consumption of gas amounted to 32 cubic feet per horse-power
per hour: being less than that of the Otto and Langen engine by about
18 per cent. But the steadiness of action of this engine adapts it to
high as well as low powers; and it works silently, while the one just
mentioned creates an intolerable din. It is obvious that the Brayton
engine might be made double-acting by employing separate pumps for the
reservoir.
Since this article was originally
prepared (1875) a new form of
gas-engine has been constructed by Mr. Otto, one of the patentees of
the Otto and Langen engine, above described, in which the objection to
that engine - viz. The noise produced by it in working - has been
wholly overcome. It is known as the "Otto silent gas-engine." In this
the working cylinder is horizontal, and its length is much less than
the original Otto and Langen engine. It is preferred to the Brayton
motor by some who have used both, but it is rather more expensive; and
in localities where public gasworks do not exist its running-cost is
likely to be against it. When circumstances favor, it seems to be
regarded as the most advantageous form of gas-engine yet produced.
F. A. P. BERNARD.
From Johnson's
(revised) Universal Cyclopaedia: A Scientific and Popular
Treasury of Useful Knowledge, published by A.J.
Johnson & Co., Davenport, Iowa (1886), Vol III, pages 383-384.
(source)
