IMPROVEMENTS IN CALORIC ENGINES."
Year: 1878

page_text: PROVISIONAL SPECIFICATION left by Matthew Piers Watt Boulton at the
Office of the Commissioners of Patents on the 7th November 1878.
MATTHEW PIERS WATT BOULTON, of Tew Park, in the County of Oxford.
IMPROVEMENTS IN CALORIC ENGINES."
This Invention relates to engines in which air or elastic fluid is heated within a
close vessel at high pressure, and employed as working fluid in the engine.
It is applicable whether the fluid be heated by external agency or by combustion
caused to take place within the close vessel.
In an engine constructed according to this Invention the following are main
parts: A heating vessel in which air or elastic fluid is heated. A cylinder fitted
with a piston which drives the engine, and a chamber in constant communication
with the cylinder, within which an instrument works, creating current of air or of
elastic fluid. This chamber, and the air or fluid within it, is alternately heated and
cooled,.and I call it the alternator.
I consider it best that the instrument working within it should be a rotary one,
and I speak of it as the fan.
In connection with the above named vessels are passages governed by valves, so
that the current created by the fan is variously directed, as will be subsequently
explained.
In an engine constructed according to this Invention the general course of opera-
tions is as follows:-
The fluid having performed work, the circulation or current caused by the fan is
directed in such a way as to produce cooling action, so that the cylinder and
alternator are filled with cold fluid, and the inetal surfaces in contact with this arc
cooled.
In the next stage the piston compresses the fluid, and meanwhile circulation i
directed through the cylinder and alternator. A considerable portion of the heat
of compression is imparted to the metal in contact with the circulating fluid, and is
stored in this metal. This abstraction of the heat of compression lightens the task
imposed on the engine during this stage.

page_text: In the next stage the circulation is directed so as to produce heating effect, and
the temperature both of fluid and metal is raised to its maximum.
Finally, in the fourth stage, expansion of the fluid takes place, and meanwhile
the circulation is again directed through the cylinder and alternator. A large
portion of the heat of the metal is imparted to the expanding fluid, and so utilised
in producing motive power. This stage continues till the fluid has expanded so far
as is judged useful.
These four stages fill up the round of operations.
In engines constructed according to this Invention there are two principal
varieties of construction. The exhaust may be discharged into the atmosphere, and
fresh air or fluid taken in to supply its place, or the fluid which has performed
work may be cooled without discharge into the atmosphere, and used over again.
I shall first take the case of an engine which is supplied with air from the
atmosphere and discharges its exhaust into this (I shall speak of the fluid during
all the operations as air), supposing that internal combustion is not employed. I
suppose the cylinder to be verticle, and the working stroke the upstroke. I confine
myself to the single action.
The air having performed work in the upstroke, so far as is desired, the passage
for internal circulation is closed and 'the eduction valve opened. Some discharge
of exhaust takes place. After this, the valve provided for the purpose being opened,
the fan expels the warmer fluid occupying the space beneath the piston, and replaces
this with cold air drawn in from the atmosphere. The metal is cooled.
This operation continues until the piston has completed a certain portion of the
return or down stroke, viz., till it has reached the point when the space beneath it
contains the proper charge of air.
$
At the end of this stage the communication with the atmosphere is closed and
the passage of internal circulation opened. The piston by its advance compresses
the air, driving it into the alternator. The metal acquires, heat, and a considerable
portion of the heat of compression is abstracted by it and stored in it.
The piston being now at or near the end of the down stroke, the valve for internal
circulation is closed and communication opened with the heating vessel. Hot air
from this enters the alternator and compresses the air in it if it be at lower pressure,
thus equalising the pressures in the two vessels.
Passage for heating circulation is now opened, and the fan causes displacement,
sending the charge of air into the heating vessel while it draws in hot air from it
till finally the space beneath the piston is filled with hot air. This operation con-
tinues till the piston has completed a certain portion of its up-stroke.
Communication with the heating vessel is now closed and the passage for internal
circulation is opened. The air expands, driving the piston. Heat is abstracted
from the metal and imparted to the expanding air, being so utilised in producing
motive power.
This stage continues till the working air has expanded so far as is judged
proper.
These four stages fill up the round of operations.
It will be understood that the timing of the operations may be somewhat
varied.
The amount of compression may be much varied, according to the objects aimed
at. It may be null, or it may be continued up to a pressure equal to that within
the heating vessel, and may be varied within these limits as thought proper.
The construction above described may be modified by making the heating vessel
to be always in communication with the alternator, so that the pressure in the
former rises and falls with that in the latter. But I consider that the construction
previously described, in which the heating vessel is maintained at high pressure, and
separated from the alternator by valves, is the more advantageous one.
Double action may be produced by duplicating the necessary parts; but in some
cases it may be convenient not to do this. In such a case the return of the piston
may be caused by means of compressed air. When this is done the end of the

page_text: cylinder opposite to that which receives the heated air is in constant communication
with compressed air contained in a vessel.
To replace loss by leakage from this vessel air may be supplied to it by a feed
pump, the supply to which is governed by the pressure in the vessel.
In the previous description of the course of operations in the engine I spoke of
the fluid employed as air; but if internal combustion be employed as the heating
means, then the working fluid will be products of combustion.
If external heating is used the products of combustion discharged from the
furnace may pass away at a high heat.
This may be utilised by the employment of regenerators, so that the heat
imparted to them by the passage of the hot gases afterwards heats the air which
feeds the fire. The regenerators may be made of small size, and may change their
function at each stroke.
In the above account I described an engine which discharged its exhaust into the
atmosphere, and took in its supply from this. The general construction remaining
the same, the exhaust may be discharged into a vessel or chamber maintained at
any pressure desired, and the supply taken in from this. The temperature within
the vessel is kept low by flow of water, or by any suitable cooling agency.
current of air produced by the engine is one agency which may be employed. The
exhaust is cooled within the vessel; the supply is taken from the air or fluid already
cooled.
A
By employing a vessel of this kind maintained at a pressure considerably above
the atmospheric, the bulk of cylinder and moving parts may be greatly reduced.
In this, as in the preceding case, the construction admits of modification, viz., by
making the heating and cooling vessels to be always in communication with the
alternator, so that the pressure in all the vessels rises and falls simultaneously, as
in Stirling's engine.
But I consider that it is better to make the heating and cooling vessels separate
vessels maintained at different pressures.
Loss by leakage of the high pressure air may be replaced in the manner previously
explained. In some cases, where it may not be desirable to use pumps for this
purpose, a fluid may be employed which is easily generated under pressure, such, for
instance, as carbonic acid gas or carbonic anhydride.
For its generation sulphuric acid may be caused to drop upon carbonate of lime,
the supply of acid being regulated by a governor controlled by the pressure within
the vessel.
For the heating and cooling vessels many known forms of construction may be
employed. These consist generally of arrangements of pipes or tubes presenting
extended surfaces to the heating or cooling agency.
The following is a construction which I consider suitable and more particularly
adapted for the heating vessel-Within a cylindrical casing placed vertically I
provide a cylindrical fire box surrounded by an annular air space. From this space
a number of tubes bent to shape project into the fire box, the limbs of the U
lying horizontally. The fire is contained in a chamber of refractory material below
the fire box, communicating therewith by a central opening. By means of a suit-
able baffle I cause the flame and products of combustion to play round and between
the tubes on their way to the upper part of the fire box, whence they pass away by
a chimney.
The baffle may itself be an air space of cylindrical form, having tubes similar to
those above described projecting from it into the fire box.