IMPROVEMENTS IN CALORIC ENGINES
Year: 1879

page_text: LETTERS PATENT to Matthew Piers Watt Boulton, of Tew Park, in the
County of Oxford, for the Invention of "IMPROVEMENTS IN CALORIC
ENGINES."
Sealed the 8th April 1879, and dated the 7th February 1879.
PROVISIONAL SPECIFICATION left by the said Matthew Piers Watt
Boulton at the Office of the Commissioners of Patents on the 7th February
1879.
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.
In an engine constructed according to this Invention the following are main
parts.
A heating vessel is provided within which air or elastic fluid is heated at high
pressure. This may be done either by the heat of a fire acting externally, or by
combustion caused to take place within the vessel.
A cylinder is provided fitted with a piston which drives the engine, which piston
is furnished with a shield to obstruct passage of heat.
A vessel is provided fitted with a piston or moveable diaphragm for causing
displacement of air or elastic fluid. This vessel may be a cylinder fitted with an
ordinary piston, or it may be a segment of a cylinder fitted with a piston blade
rocking on an axis.
Charges of cold air are received in this vessel and transferred from it to the
heating vessel, and it also receives charges of hot air, which perform work in the
cylinder of the engine. I call this vessel the charging vessel, and the instrument
working in it the displacer. The displacer is furnished with a shield to obstruct
passage of heat.
Two passages are provided between the charging vessel and the heating vessel,
and a regenerator is provided communicating with one of these, being placed
between the heating vessel and the charging vessel.
A pump is also provided for compressing air or elastic fluid. This pump may be
of any known form, thus it may have a piston working in a cylinder, or it may be
a rotary pump working by pressure.

page_text: A vessel is provided which receives and contains the air or elastic fluid compressed
by the pump. I call this the air vessel.
The pressure maintained in this air vessel is higher than that of the atmosphere
or-source-of.supply, but lower than that in the heating vessel.
The pump may be dispensed with, but I consider its use generally desirable in
order to obtain greater expansion and greater thermal economy.
The degree of compression produced by the pump may be varied at pleasure.
Cooling agency-is applied to the vessels in which compression of air or elastic
fluid takes place.
In some cases, in addition to the parts above mentioned, a refrigerator or cooling
vessel is provided into which the exhaust from the engine is discharged, and whence
when cooled it is delivered back as supply; but in other cases this is dispensed
with, the exhaust being discharged into the atmosphere and the supply taken
from it.
In proceeding to describe the course of operations I shall confine myself first to
one form of engine, and afterwards point out some modifications.
I shall take the case of an engine which discharges its exhaust into the air, and
shall speak of the fluid throughout as air.
I shall suppose, for starting point, that the piston has just finished its working
stroke and is about to commence its return stroke.
The displacer moves towards the eduction end of the charging vessel. On its
advancing side it expels, exhaust, while, behind it draws in air through a suction
valve. When it has reached, or nearly so, the end of its stroke, the eduction valve
is closed and communication is opened between the charging vessel and the air
vessel. Air from the air vessel rushes into the charging vessel and raises the
pressure in it, whereupon the communication between these two vessels is closed.
Communication is now opened between the charging vessel and the heating vessel
on both sides of the displacer, so that it is placed in equilibrium. The air from the
heating vessel entering at the eduction end of the charging vessel is hot, but that
entering at the opposite or supply end is cool, having passed through the regene-
rator and imparted heat to the plates or bodies composing it. By the entrance of air
from the heating vessel the air previously contained in the charging vessel is com
pressed and the pressure in the vessel is raised.
The displacer then returns towards the supply end of the charging vessel, sending
the air on this side into the heating vessel through the regenerator, in passing
through which it takes up the heat previously imparted to its plates by the flow of
air from the heating vessel. At the end of this stroke the charging vessel is charged
with air of the maximum working temperature and pressure. By means of the
regenerator the one side of the charging vessel is kept cool for receiving the charge
of cool air.
While the displacer has been making the two strokes above described the piston
has performed its return stroke, expelling exhaust.
Communication with the heating vessel is now closed, and communication is
opened between the hot side of the charging vessel-and-the-cylinder. The displacer
remains stationary. Hot air passes from the charging vessel into the cylinder and
expands there, driving its piston. This state continues during the working
stroke of the piston; at the end of this the point previously taken as starting point
is reached.
The required movement of the displacer may be effected in various ways. One
way is to cause it by a cam.
"
The pump may be arranged and timed in various ways. One construction for
the pumping is as follows:-The piston on its cool side acts as a pump, forcing air
in its working stroke into the air vessel. In the first part of its return stroke it is.
acted on by air from the air vessel and impelled by this, while in the latter part of
this stroke it takes in a fresh supply of air, which in its next or working stroke
it sends into the air-vessel along with that which had previously entered
from it.

page_text: In the above I spoke of the fluid in all stages as air, but if internal combustion
is employed, then products of combustion act as working fluid. When internal
combustion is used any known suitable method of supplying the fuel to the interior
of the heating vessel may be employed; but as this is no part of the present Inven-
tion I do not give any description of this.
In the above account I have described an engine which discharges its exhaust
into the atmosphere and takes 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. In this
case a cooling vessel is employed, within which the exhaust is cooled by means of
water or any suitable cooling agency. A current of air produced by the engine is
one agency that may be employed. The exhaust after having been cooled is used
over again as supply. By employing a vessel of this kind, maintained at a pressure
considerably above the atmosphere, the bulk of cylinder and moving parts may be
greatly reduced.
It is possible to use the hot end of the charging vessel as a portion of the heating
surface, whereby the metal surface of the charging vessel is more utilised. But I
consider it best with a view to thermal economy not to do this, but to keep the
heating vessel entirely apart in order that the air while expanding in the cylinder
may not receive heat from the furnace.
Again the construction might be modified by making the regenerator and cooling
vessel clearances or spaces open to the cylinder, as in Stirling's engine, but I
consider that this would be disadvantageous. One object at which I have aimed is
to work in such a way that the heating and cooling of the air shall take place in
separate vessels shut off at times from the cylinder by valves, so that these vessels
may be made as large as is desired without detriment to the action.
When a cooling vessel at high pressure is employed loss of the high pressure air
by leakage may be replaced by a feed-pump worked by the engine, the supply to
which is governed by the pressure within the cooling vessel.
Otherwise, 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 on carbonate of lime, the supply of acid being
regulated by a governor controlled by the pressure within the vessel.
Again, such a fluid may be used to raise the pressure in the vessels before the
engine is started, the pressure being afterwards maintained by a feed-pump forcing
in air.
For the heating and cooling vessels many known forms of construction may be
employed. These consist generally of arrangements of pipes or tubes présenting
extended surfaces to the heating or cooling agency. The following is a con-
struction which I consider suitable and more. particularly adapted for the heating
vessel :-
A vessel is provided from the side of which project numerous tubes bent in the
form of a U, and so placed that in each tube one of the mouths is higher than the
other. These tubes project into the flue of a furnace. The air to be heated enters
at one end of the vessel, and passes out at the other in a direction opposite to that
taken by the hot gases passing along the flue. In consequence of the difference of
level of the mouths of the tubes circulation of air always goes on through them,
and heating of the air is always maintained.
The vessel may be divided by diaphragms into numerous compartments com-
municating one with another through bent tubes or suitable passages, so as to
prevent passage of hot air back from the hotter to the cooler end of the vessel.
The vessel may have tubes projecting on both sides, its interior being divided by
a longitudinal diaphragm into two side compartments, so that the air flows along
one compartment in one direction and returns along the other, and several such
vessels with their tubes may be arranged side by side in zig-zag flues, the vessels
being in communication so as to form a continuous zig zag channel. The direction

page_text: of the flow of the air, as previously mentioned, is opposite to that of the hot gases
along the flues.
A similar construction is applicable to a cooling vessel, cold fluid being caused
to travel-in-the_one_case as hot in the other.
The construction of heating and cooling vessel-above.described is applicable to
various forms-of-air-engine.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Matthew Piers Watt Boulton in the Great Seal Patent Office
on the 5th August 1879.
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 a high pressure, and employed as working fluid in the engine.
In an engine constructed according to this Invention, the following are main
parts
-
A heating vessel is provided, within which air or elastic fluid is heated at high
pressure. This may be done either by the heat of a fire acting externally or by
combustion caused to take place within the vessel.
A cylinder is provided, fitted with a piston which drives the engine, which piston
is furnished with a shield to obstruct passage of heat.
A vessel is provided, fitted with a piston or moveable diaphragm for causing dis-
placement of air or elastic fluid. This vessel may be a cylinder fitted with an
ordinary piston, or it may be a segment of a cylinder fitted with a piston blade
rocking on an axis.
Charges of cold air are received in this vessel and transferred from it to the
heating vessel, and it also receives charges-of-hot-air, which perform work in the
cylinder of the engine. I call this vessel the charging vessel, and the instrument
working in it the displacer. The displacer is furnished with a shield to obstruct
passage of heat,
Two passages are provided between the charging vessel and the heating vessel,
and a regenerator is provided, communicating with one of these, being placed
between the heating vessel and the charging vessel.
A pump is also provided for compressing air or elastic fluid. This pump may be
of any known form; thus it may have a piston working in a cylinder, or it may
be a rotary pump working by pressure.
A vessel is provided, which receives and contains the air or elastic fluid com-
pressed by the pump; I call this the air vessel.
The pressure maintained in this air vessel is higher than that of the atmosphere
or source of supply, but lower than that in the heating vessel.

page_text: The pump may be dispensed with, but I consider its use generally desirable, in
order to reduce the bulk of the engine.
The degree of compression produced by the pump may be varied at pleasure.
Cooling agency is applied to the vessels, in which compression of air or elastic
fluid takes place.
In some cases, in addition to the parts above mentioned, a refrigerator or cooling
vessel is provided, into which the exhaust from the engine is discharged, and whence,
when cooled, it is delivered back as supply; but in other cases this is dispensed
with, the exhaust being discharged into the atmosphere and the supply taken
from it.
.
In procceding to describe the course of operations I shall confine myself, first, to
one form of engine, and afterwards point out some modifications.
I shall take the case of an engine which discharges its exhaust into the air, and
shall speak of the fluid throughout as air.
I shall suppose, for starting point, that the piston has just finished its working
stroke and is about to commence its return stroke.
The displacer moves towards the eduction end of the charging vessel.
On its
advancing side it expels exhaust, while behind it draws in air through a suction
valve. When it has reached, or nearly so, the end of its stroke, the eduction valve
is closed and communication is opened between the charging vessel and the air
vessel. Air from the air vessel rushes into the charging vessel and raises the
pressure in it, whereupon the communication between these two vessels is closed.
Communication is now opened between the charging vessel and the heating vessel on
both sides of the displacer, so that it is placed in equilibrium. The air from the heating
vessel entering at the eduction end of the charging vessel is hot, but that entering
at the opposite or supply end is cool, having passed through the regenerator and
imparted heat to the plates or bodies composing it. By the entrance of air from
the heating vessel, the air previously contained in the charging vessel is compressed
and the pressure in the vessel is raised.
ending
passing
olie flow of
essel is charged.
By means of the
receiving the charge
The displacer then returns towards the supply end of the charging ves
the air on this side into the heating vessel through the regenera
through which it takes up the heat previously imparted to its pl
air from the heating vessel. At the end of this stroke the charp"
with air of the maximum working temperature and pressur
regenerator the one side of the charging vessel is kept cool for
of cool air.
While the displacer has been making the two strokes above described, the piston
has performed its return stroke, expelling exhaust.
Communication with the heating vessel is now closed, and communication is
opened between the hot side of the charging vessel and the cylinder. The displacer
remains stationary. Hot air passes from the charging vessel into the cylinder and
expands there, driving its piston. This state continues during the working stroke
of the piston. At the end of this the point previously taken at starting point is
reached.
The required movement of the displacer may be effected in various ways. One
way is to cause it by a cam.
The pump may be arranged and timed in various ways. One construction for
the pumping is as follows:-The piston on its cool side acts as a pump, forcing air
in its working stroke into the air vessel. In the first part of its return stroke it
is acted on by air from the air vessel and impelled by this, while in the latter part
of the stroke it takes in a fresh supply of air, which in its next or working stroke
it sends into the air-vessel, along with that which had previously entered
from it.
In the above I spoke of the fluid in all stages as air, but if internal combustion is.
employed, then products of combustion act as working fluid. When internal com-
bustion is used, any known suitable method of supplying the fuel to the interior.

page_text: of the heating vessel may be employed; but as this is no part of the present Inven-
tion I do not give any description of this.
In the above account I have described an engine which discharges its exhaust
_into_the_atmosphere, and takes 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: In this case
a cooling-vessel is employed, within which the exhaust is cooled by means of water
or any-suitable.cooling agency. A current of air. produced by the engine is one
agency that may be employed. The exhaust,-after having been cooled, is used over
again as supply-By employing a vessel of this kind maintained at a pressure.
considerably above the atmosphere, the bulk-of-cylinder and moving parts may be
greatly reduced.
It is possible to use the hot end of the charging vessel as a portion of the heating
surface, whereby the metal surface of the charging vessel is more utilized; but I
consider it best with a view to thermal economy not to do this, but to keep the
heating vessel entirely apart in order that the air, while expanding in the cylinder,
may not receive heat from the furnace.
Again, the construction might be modified by making the regenerator and cooling
vessel clearances, or spaces open to the cylinder, as in Stirling's engine; but I
consider that this would be disadvantageous. One object at which I have aimed is
to work in such a way that the heating and cooling of the air shall take place in
separate vessels, shut off at times from the cylinder by valves; so that these vessels
may be made as large as is desired without detriment to the action.
When a cooling vessel at high pressure is employed, loss of the high pressure air
by leakage may be replaced by a feed pump worked by the engine, the supply to
which is governed by the pressure within the cooling vessel.
Otherwise 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 on carbonate of lime, the supply of acid being
regulated by a governor controlled by the pressure within the vessel.
Again, such a fluid may be used to raise the pressure in the vessels before the
engine is started, the pressure being afterwards maintained by a feed pump forcing
in air.
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 :-
A vessel is provided, from the side of which project numerous tubes bent in the
form of a U, and so placed that in cach tube one of the mouths is higher than the
other; these tubes project into the flue of a furnace. The air to be heated enters
at one end of the vessel and passes out at the other in a direction opposite to that
taken by the hot gases passing along the flue. In consequence of the difference of
-level-of-the mouths of the tubes, circulation of air always goes on through them,
and heating of the air is always maintained.-
The vessel may be divided by diaphragms into numerous compartments-commu--
nicating one with another through bent tubes or suitable passages, so as to prevent
passage of hot air back from the hotter to the cooler end of the vessel.
The vessel may have tubes projecting on both sides, its interior being divided
by a longitudinal diaphragm into two side compartments, so that the air flows along
one compartment in one direction and returns along the other, and several such
vessels with their tubes may be arranged side by side, in zig-zag flues, the vessels
being in communication so as to form a continuous zig-zag channel. The direction
of the flow of the air as previously mentioned, is opposite to that of the hot gases
along the flues.
A similar construction is applicable to a cooling vessel, cold fluid being caused to
travel in the one case as hot in the other:

page_text: DESCRIPTION OF THE DRAWINGS.
Fig. 1 is a longitudinal section partly in elevation; Fig. 2 is a transverse section
on the line X, X; Fig. 3, a transverse section on the line Y, Y of Fig. 1; and Fig. 4
is a plan partly in section of a caloric engine according to my Invention; A is the
cylinder within which works the piston a, provided on the back with a shield a'.
The piston rod is connected by a connecting rod a² with a crank on the main shaft S
which has on it a fly wheels and several cams for working the displacer and the
valves, as will hereafter be explained; B is the air vessel of cylindrical form com-
municating with the front end of the cylinder A by a passage b, and with the
charging vessel C by a passage b'. The passage b is provided with a slide valve b²,
worked by the cam 82. The passage 61 is also provided with a slide valve 6s worked
by the cams. There is an opening into the passage b' fitted with a self-acting
suction valve b; C is the charging vessel having the form of a segment of a
cylinder in which works the displacer c, rocking upon an axis c¹. The displacer is
worked by a cam 8¹ on the main shaft S; acting on a lever c², which is connected to
an arm c on the axis c¹. The lever may be urged in the one direction by.a
weight or spring, so that the roller at its upper end is made to bear against the
periphery of the cam 81, or that cam may have a grooved cam path, so as to work
the lever c in both directions, in which case the weight or spring is dispensed with:
The charging vessel C communicates with the back end of the cylinder A by a
passage cgoverned by a shut off valve c, which is worked by the cam. 85. The
charging vessel Calso communicates with one end of the heating vessel D by a
passage c; and also by a passage c? through the regenerator E with the other end of
the heating vessel. Both the passages c and c' are provided with shut off valves
c8, which are simultaneously moved by bell crank levers worked from the cam 8.
The heating vessel D, as shewn in the Figures, consists of two horizontal tubes d,
connected by a number of arched tubes d, forming a vaulted flue through. which
pass the flames and hot products of combustion from the fire d² on their way to the
chimney . The heating surface may be increased by the addition of the U tubes
d. The heating vessel is enclosed in brickwork d³, which forms a foundation. for
the engine. Diaphragms do extend across the tubes & so as to cause the air to pass
through the arched tubes d' instead of flowing uninterruptedly along the tubes d..
The regenerator E is a vessel containing a number of rods, perforated plates, or pieces
of wire gauze, exposing an extended surface of conducting material.
The cylinder
A has at its front end a selfacting suction valve a³, and at the back end a slide
valve for eduction a', which. is worked from the cam or eccentric 8. This construc-
tion may be modified dy dispensing with the air vessel. B and its connections with
the cylinder and charging, vessel, the cylinder being in that case open in front. I
will first describe the course of operations when this simpler form is adopted.
I shall suppose, for starting point, that the piston.a is at.the left hand end of the
cylinder A. and has just finished its working stroke. The displacer c is at the left
hand end of the charging vessel C. Communication is open between the charging
vessel, C and the cylinder A through the passage c, the valve c5 being unseated, the
eduction valve a' is opened, the piston a moves towards the right hand end of the
cylinder A, expelling exhaust through a. The displacer c moves towards the right
hand end of the charging. vessel C. On the right it expels exhaust through the
passage into A, which passes out along with the other exhaust through at; on the
left it draws in air through the suction valve b*; when chas reached or nearly so
the end of this stroke, communication between C and A is closed by closure of the
valve c³, and communication is opened between C and the heating vessel D on both
sides of c by opening of the two valves c³, air from D rushes into C, compressing the
air in it. The air from D entering through the passage c7 is cooled by passing
through the regenerator E, while the air entering through the passage co enters at

page_text: full heat; the displacer c now returns towards the left hand end of the charging
vessel C, moving with equal or nearly equal fluid pressure on both sides; on the
left it sends the air into the heating vessel D through E, in passing through which it
becomes heated by the heat previously deposited in E. On the right it is followed
by-hot-air-entering from D through the passage cº. At the end of this stroke C
is charged with air of the maximum working temperature and pressure: --
While c has been making the two strokes above described, the piston a has per-
formed its stroke from left to right, expelling exhaust through the valve at.
This valve is now closed, as-also-are-the.two_valves cs, and the valve c³ is opened;
the displacer c remains stationary. Hot air passes from the charging vessel C-into
the cylinder A and expands therein, driving-its-pistou. This state continues during
the working stroke of the piston. At the end of this stroke the point previously
- taken as starting point is reached.
When the full construction, as shewn in the Drawings, is employed, including the
air vessel B and its connections,. the action is as follows:-
When c, the displacer, has completed its stroke from left to right and communica-
tion is closed between the charging vessel C and the cylinder A, communication is
opened between the air vessel B and the charging vessel C by opening of the valve b³,.
and air from B rushes into C, raising the pressure of the air in it. This having
been done the valve 63 is closed. After this the. two valves c8 are opened, as
described above. The compression of the air is effected by the piston a in the fol-
lowing manner :-When a moves from left to right it draws in air through the
suction valve a³, and in the succeeding stroke from right to left it compresses this
air and forces it into the air vessel B through the valve 62. The quantity of air
drawn in through the valve a³ admits of being regulated by the timing of the
closure of the valve b². In the first part of the back stroke of the piston a this
valve is open so that air enters the cylinder A from B and drives the piston. At a
certain point of the stroke the valve 62 is closed and subsequently the pressure falls,
and in the latter part of the stroke air enters through the suction valve a³. The
timing of the closure of the valve 62 may be regulated by the pressure in the
vessel B.
Having thus described the nature of my Invention and in what manner the same
is to be performed, I claim,-
First. The use of a caloric engine wherein successive charges of cold air or elastic
fluid received in a charging vessel are by the movements therein of a displacer or
piston working with equal fluid pressure on both sides passed through a heating
vessel back to the charging vessel before they are in communication with the cylinder
in which they afterwards successively perform work.
Second. In a caloric engine operating as above described, the arrangement of a
regenerator between the heating vessel and the charging vessel so as to keep the
supply side of the latter cool.
Third. In a caloric engine operating as above described, the use of a supply reser-
voir, into which the air or working fluid is compressed by the engine, and from
which it is admitted-to-the-charging-vessel.
Fourth. The construction of caloric engine hereinbefore described with reference
to the accompanying Drawings.
In witness whereof, I, the said Matthew Piers Watt Boulton, have hereunto set
my hand and seal, this Seventh day of May, in the year of our Lord One
thousand eight hundred and seventy nine.