IMPROVEMENTS IN HOT AIR ENGINES
Year: 1861

page_text: LETTERS PATENT to Philander Shaw, of Boston, in the County of Suffolk,
in the State of Massachusetts, one of the United States of America, for
the Invention of “IMPROVEMENTS IN HOT AIR ENGINES.”
Sealed the 11th January 1862, and dated the 19th July 1861.
PROVISIONAL SPECIFICATION left by the said Philander Shaw at the
Office of the Commissioners of Patents with his Petition, on the 19th
July 1861.
I, PHILANDER SHAW, of Boston, in the County of Suffolk, in the State of
Massachusetts, one of the United States of America, do hereby declare the
nature of the said Invention for "IMPROVEMENTS IN HOT AIR ENGINES," to be
as follows:-
First, in the arrangement of two single-acting cylinders on either side of a
furnace and its adjuncts, the former being located partly upon and partly
within, and the latter wholly within an air-tight case, which receives com-
pressed air, which is therein expanded by heat, the pistons of the said cylinders
being coupled to one shaft, having its cranks at or nearly at right angles with
each other, and the air-tight casing which makes the foundation for the
engine, being so divided by means of diaphragm plates and partitions, as to
direct the incoming currents of compressed air against those portions of the
machine which receive the products of combustion, so that the said currents

page_text: absorb the heat radiated from the said portions, and are gradually heated on
their way to the furnace, while the desideratum of having a comparatively cool
surface to the exposed portions of the engine is attained.
Second, in a peculiar arrangement and construction of a trunk or tube in con-
*nection with the packed portion of the piston, the finished part of the cylinder,
the cylinder head, the trunk packing, the air inlet and outlet valves, and other
-accessories by which a pump is formed to supply compressed air to the air-
tight casing or receiver and furnace, where it is expanded by heat, and then
supplied to cylinders; the said pump being operated in compressing the air
direct from the engine piston without the strain necessary for that purpose
-being passed through the rotative parts of the mechanism.
Third, in a peculiar construction of the hot air cylinder, by which an oil cup
is formed entirely around it, at that part where the lowest edge of the piston
comes at the lowest point of its downward stroke, by which the frictional
surfaces of the piston and cylinder are kept lubricated, and in a peculiar
arrangement of oil cup at the said location, by which the oil is prevented from
burning and from evaporation.
Fourth, in the construction and arrangement of an inwardly projecting
flange in the cylinder just below the groove, mentioned with reference to the
contracted and elongated lower part of the piston, which said flange nearly,
but not quite touches, the purpose of the said flange being to deflect such solid
products of combustion as may enter the cylinder with the gaseous products,
and to keep them from abrading the frictional surfaces of both cylinder
and piston.
Fifth, in the employment of an auxiliary valve, so arranged and operated as
to admit air which is pure, compressed, and comparatively cool at or near the
top of the clearance space in the cylinder, for a double purpose, first, to
balance the pressure on the large inlet valve, so as to reduce the force required
to work it; and, second, to keep the frictional surfaces of the piston and
cylinder comparatively cool.
Sixth, in regulating the speed of hot air engines by the employment of a
"regulator" to operate a valve to control the amount of compressed air
admitted to act upon the engine pistons, instead of employing the regulator, as
formerly practised in hot air engines, to open a valve to discharge the generated
pressure, thereby causing a loss of heat.
Seventh, in the employment of a close receptacle, through which the
exhaust is made to pass (which receptacle should have a sufficient amount of
heating surface) within the air-tight reservoir, into which the air is compressed.

page_text: and made to circulate through on its passage to the furnace, so that the
currents of air shall impinge upon the outer surface of the said receptacle, and
shall abstract from the "exhaust" some of its heat, which is transmitted
through the material of the said heater.
Eighth, in the utilization of the caloric contained in the exhaust by employ-
ing it to generate steam, which may be employed to work a steam engine
auxiliary to the hot air engine, or for other purposes.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Philander Shaw in the Great Seal Patent Office on the
18th January 1862.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, PHILANDER
SHAW, of Boston, in the County of Suffolk, in the State of Massachusetts,
one of the United States of America, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Nineteenth day of July, in the twenty-fourth year of
Her reign, did, for Herself, Her heirs and successors, give and grant unto
me, the said Philander Shaw, Her special license that I, the said Philander
Shaw, my executors, administrators, and assigns, or such others as I, the said
Philander Shaw, my executors, administrators, and assigns, should at any time
agree with, and no others, from time to time and at all times thereafter during
the term therein expressed, should and lawfully might make, use, exercise,
and vend, within the United Kingdom of Great Britain and Ireland, the
Channel Islands, and the Isle of Man, an Invention for "IMPROVEMENTS IN
HOT AIR ENGINES," upon the condition (amongst others) that I, the said
Philander Shaw, by an instrument in writing under my hand and seal, should
particularly describe and ascertain the nature of the said Invention, and in
what manner the same was to be performed, and cause the same to be filed in
the Great Seal Patent Office within six calendar months next and immediately
after the date of the said Letters Patent.
NOW KNOW YE, that I, the said Philander Shaw, do hereby declare
the nature of my said Invention, and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement, that is to say:-
The nature of my Invention consists first, in an arrangement substantially
such as herein is described, and also illustrated by the Drawings of two single

page_text: acting cylinders having their pistons coupled to a shaft, with its cranks at right
angles with each other, with a furnace and its accessories centrally located
between the said cylinders and within an air-tight casing, which forms a reser-
voir for compressed and heated air, and is so divided by partitions and diaphragm
plates as to receive the cool supply air at and near the exterior of the reservoir,
and to guide it inward toward the furnace in such a direction that it shall
absorb the heat radiated from such parts of the engine as receive the products
of combustion, those parts of the cylinders in which the pistons fill the bore
being located without, and upon the casing, and exposed to the atmosphere, and
the other parts of the cylinder being located within the casing, so as to impart
the heat radiated from them to the compressed air on its passage to the
furnace.
Second, in a peculiar construction and arrangement, substantially such as
herein is described, and also illustrated in the Drawings of the hot air cylinder,
the packed part of its piston and a piston trunk, which with the necessary
packing valves and other adjuncts from a pump, by which cold air is com-
pressed and supplied to be expanded by heat, the pump being annular and
exposed to the cooling influence of the atmosphere, and being operated by the
direct pressure of the expanded air on the engine piston (when compressing
the supply air), the force necessary for that purpose is not passed through the
rotative parts of the mechanism, and facility is obtained for, connecting the
pitman which vibrates within the trunk direct to the piston, and for keeping
the connecting joint cool by free atmospheric exposure, with good facilities
for lubrication.
Third, in a construction of the cylinder, substantially such as herein is described
and illustrated in the Drawings, and more particularly detailed on Sheet
No. 3, Figure 6, which consists in a groove formed around the inner side of
the cylinder at that part where the lower edge of the closely fitting portion of
the piston comes at the lowest point in its downward stroke, which groove
serves to receive the lubricating fluid which escapes past the packed portion
of the piston, and also such as may be directly introduced into it by means of
"oil pumps," &c. The lower edge of the piston may be made to dip in the
fluid in the groove, and so lubricate the inner surface of the cylinder at each
upward stroke of the piston. The groove may be made to receive an isolated
circular trough as shown in Figure 6, to hold the oil, which by means of the
fifth part of my Invention will prevent evaporation thereof by conducted heat,
which might occur without the use of the isolated trough.
Fourth, in the construction of an inwardly projecting flange as shown and

page_text: described, which flange may form part of the boundary of the circular groove
above referred to, and comes nearly but not quite into contact with the
contracted and extended part of the piston, for the purpose of deflecting such
solid products of combustion as may find their way with the gaseous products
into the space within the cylinder, and thus prevent them from abrading the
finished upper part of the cylinder.
Fifth, in the employment of an auxilliary valve operating to admit from
the supply pump or receiver comparatively cool pure compressed air into the
clearance spaces within, and connected with the cylinder for the double purpose
of balancing the pressure on the inlet valve into the cylinder, and to maintain
the frictional surfaces of the piston and cylinder cool enough to be kept
lubricated. When the isolated oil trough is employed, the cool air passing
round it from this auxilliary valve, cuts off from the oil the conducted heat
which might otherwise evaporate it.
Sixth, in regulating the speed of hot air engines, by controlling the flow of
the air under pressure to the engine pistons, by means of a regulator operating
to work a valve, for this purpose, instead of permitting the regulator to open
a valve for the escape and consequent loss of the generated pressure as
formerly practiced in regulating the speed of hot air engines.
Seventh, in the employment of a close receiver for the "exhaust," with a large
radiating surface within the air-tight reservoir into which air is forced, and
then expanded by heat for the purpose of imparting from its outer surface a
portion of the caloric contained in the "exhaust" to the surrounding currents.
of incoming compressed air.
Eighth, in the utilization of the caloric escaping with the "exhaust," by em-
ploying it to generate steam, substantially as described, which, when generated,
may be made to operate through any well-known steam engine and air pump.
to aid in the compression and supply of air to the caloric engine, or the steam
thus generated may be employed in any well-known way.
DESCRIPTION OF THE DRAWINGS.
Figure 1, Sheet No. 1, illustrates in half side elevation, and in half sectional
clevation, a hot air or caloric engine embodying my Invention, the section
being taken in the lines y, y, Figure 2, and z, z, Figure 3.
Figure 2, Sheet No. 2, is an end elevation of the same, a part however
being shown in section taken in the lines y¹, y¹, Figure 1, and a, a, Figure 3,
for the purpose of showing the fuel feed box.
Figure 3, Sheet No. 3, illustrates in half plan and half horizontal section,

page_text: taken in the lines '2', ', Figure 1, and 2, 22, Figure 2, a hot air engine
embodying my Invention.
Figure 4, Sheet No. 8, is a sectional elevation of a boiler made on a smaller
scale than are the other Figures of the Drawings, and designed to be connected
with the exhaust of the hot air engine to utilize the escaping heat; Figure 5
is a sectional elevation taken in the line y2, y2, Figure 3, of so much of the
cylinder and parts connected therewith as to illustrate how the exhaust
escapes into the radiator or heater; Figure 6 shows in section the groove in
the cylinder, the isolated oil trough therein, and the inwardly projecting flange
on a scale enlarged from the other Figures. Throughout all the figures of the
Drawings, similar letters and characters refer to similar parts. E is the casing,
which as it forms the reservoir for the compressed heated air, the foundation
or bed-plate for the mechanism should be so made as to be air-tight under
the heat strains and pressure to which it is subject, and wherever moving
parts pass through it, they should be carefully packed. Centrally located in E
is the furnace lined with the fire-brick J, provided with grates c, and an ash-
pit, which has an air-tight door I, and fuel receptacle H, from which fuel is
fed to the fire through the top of the furnace. This fuel box H is provided
with an air-tight receiving door d, having suitable fastenings, and a valve e,
opened and closed by a link f and valve rod, which passes through a packing
box. A piston g, with its rod h, passing packed through H, serves to thrust
the fuel forward, so that it will fall through the aperture which the valve e
serves to close. By this arrangement and its proper manipulation, which
needs no explanation, it is obvious the fire may be replenished with fresh fuel
while there is the requisite pressure of hot air within the furnace needed to
operate the engine, and without impeding the movement thereof. The furnace
is provided with openings a¹ below the grates, and others a² above the top of
the fuel, through which air under pressure is supplied by means herein-after
to be described, which air is introduced into the space contained between the
outside casing 6 of the furnace, and the casing t which next surrounds it. The
working cylinders, of which there are two, are located within and upon E, and
on opposite sides of the furnace. These cylinders are single acting, that is,
the piston of each is forced upward by the action of heated, air, and both
being connected to the same shaft R by cranks at right angles with each other
the downward movement of each piston is produced by the upward movement
of the other, acting through the shaft in connection with the fly wheel.
Each cylinder may be described as in two sections, the upper section A
standing above the bed plate, and being bored out so that a packed piston D

page_text: may move freely therein after the manner of steam engine pistons within their
cylinders. The lower section B is within the bed plate, for the reception of
the extension F of the piston, and need not be bored or finished, as the exten-
sion of the piston is not intended to fill the cylinder, but leaves (when the
piston is at the extreme of its downward stroke) an end clearance as well as
an annular space around it. That part of the piston which is marked D, is
constructed nearly like steam engine pistons so far as packing is concerned,
and does not need further explanation than is afforded by the Drawings.. The
follower c is the flange of the pipe or trunk C, which is open at the top, and
in which the connecting rod P plays. The trunk passes through the upper
head of the cylinder, where it is packed with leather, and guided by the
gland x. The head is furnished with valves n to admit air into the annular
space between A and C, and with an outlet valve o, which permits, when open,
the air within the said space to pass into the casing through the valve box K
and pipe L. Reciprocating movement imparted to the pistons is made to rotate
the shaft R in a manner so plainly shown in the Drawings, as not to need any
description here. Supposing the engine to be in motion, the air which is
taken in by the pumps at each downward stroke of the pistons, is compressed
and thrown out by the upward strokes thereof, and passes as is indicated
by the arrows along the division plate j, which extends entirely across the
space enclosed within E, to an opening in the centre of j, then between
plates j and k, then downward between the outer wall of E, and an internal
vertical partition m parallel with E, which extends entirely around within E,
and parallel to its vertical wall, then vertically between partitions m and 7,
into a space contained between 1 and t, whence the air passes to the fur-
nace through openings in t, and the openings a¹ and a³ before described, the
position of the damper ŕ determining the proportion of air admitted above and
below the fuel.
j
Having described how air is compressed and forced into the furnace, I will
now show how, when expanded by heat, it passes into the cylinders and is
exhausted therefrom, thereby producing reciprocation of the pistons within
them, and developing the power generated by heating the air. In the top of
the furnace, and passing through it to the inlet valve boxes O, is a suitably
shaped pipe with an opening into it, which a throttle valve p operates to open
and close in the usual way by a governor Q, dependant on the speed of the
engine, and acting through the connection q. The heated air and gaseous pro-
ducts of combustion mingled pass into this pipe, and when the inlet valve is
opened, pass
sinto the cylinder and force the piston upward.

page_text: The inlet valve closes when or before the piston has completed its stroke,
and the exhaust valve opens and permits the contents of the cylinder to
escape into the open air, through the passage N, and radiator or heater G, located
in the space through which air passes, on its way to be heated in the furnace.
The valves shown in the Drawings are of the poppet variety, and are operated
at proper times by lifter toes on the valve rods, and on rocker shafts worked
from eccentrics S, on the shaft. There is nothing peculiar about the valves
or valve gear, and any other which is adapted to the ingress and egress of the
heated air, and known to engineers in the practice of their profession, may be
used for those shown, though I prefer to use valves of the poppet variety.
The form of the heater is immaterial, that shown presents a large surface
for radiation, and the diaphragm plates a, compel a tortuous passage of the
" exhaust."
It will be seen that the disposition of division plates and partitions, before
mentioned, is such as to cause the gradual heating of the cold air, on its way
from the pump to the furnace, by absorption of the heat, which radiates from
the part of the cylinder filled with hot air, from the conveying pipes, heater
and boundaries of the furnace, so that the radiated heat is nearly all utilized,
and the convenience is attained of having a comparatively cool surface to the
outer or exposed parts of the machine. A dead air space is formed in E
between its base plate and the reservoir of compressed and heated air to
prevent radiation from the lower surface. At the junction of the upper
and lower sections A and B, of the cylinder, and at the lower edge of the
close fitting part D of the piston, a groove or channel v, is formed entirely
around the cylinder, as shown in Figure 1. At the upper edge of B, there is
an inward projecting belt or flange s, which forms the bottom of the groove and
extends inward from the general surface of B, so as almost to touch the lower
or extended part F, of the piston. The groove or channel round the cylinder
communicates with the compressed air in the upper part of E, by means of
the pipe W, which terminates in the valve box 61, in which the poppet valve u
operates by any suitable mechanism, that shown being a wiper or arm on a
rocker shaft acting on the valve stem, to open the valve against a spring, the
reaction of which closes it. It will be seen that when the valve u, is opened
air will flow from the space in E, above j, into the cylinder, and if this valve
is opened as it should be, after the exhaust valve closes, and before the main
inlet valve opens, that all clearance or unoccupied space in the cylinder
and valve passages will be filled with air having a pressure equal to that
within the air reservoir. The air taken into the cylinder through the

page_text: valve u, will be that directly from the pump, and free from gaseous and
solid products of combustion, and moreover it will be comparatively cool.
The object of introducing air through w, from and at the places and at
the time mentioned, is threefold. First, by rendering the pressure alike on
both sides of the inlet valve, the force required to be exerted is reduced
to the minimum. Second, by having the spaces in the cylinder filled with
pure air, that which rushes into the cylinder from the combustion chamber,
to displace the piston, will not carry the products of combustion into the
spaces so occupied, and as the valve u and the main inlet valve are designed
to be closed together, it will be evident that the annular space between the
extension part F, and the upper or finished part A of the cylinder, formed
as the piston rises in the cylinder, will be kept filled with pure air, to the
exclusion of the impure air, which will fill the body of the cylinder. Third,
the packing of the piston will thus be exposed at its upper and lower edges
to cool air, while the sliding surface of the packing will act upon that part
of the cylinder which is exposed both upon its interior and exterior to air of
the ordinary temperature. By the described arrangement and devices, I
am enabled to pack my piston as closely, and to keep it as well lubricated
as any steam engine, or air pump piston. The inwardly projecting flange s
serves to deflect or render difficult the passage of any particle of solid matter
coming into the cylinder with the heated air and gaseous products of
combustion, and the lower edge of the packed portion of the piston is of
the form shown in the Drawing, Figure 1, to aid in deflecting solid particles
to keep the sliding surface of the piston from abrasion by them. The before-
mentioned groove v, around the cylinder, serves to catch the oil which
passes the packed piston, or oil may be forced into it by a syringe, and a
pipe provided with a stop cock will afford means for drawing off any
accumulation of lubricating material which may gather there, while the
lower edge of the packed part of the piston, by dipping into the oil at
each downward stroke, will aid in keeping the working surfaces well
lubricated. To prevent burning the oil by the heat absorbed and conducted
by the material of the cylinder, I place within the groove a circular oil
trough M, see Figure 6, which is maintained at a little distance from
the metal of the cylinder by ears placed at intervals around the trough;
the current of cool air from the auxilliary valve, will pass through this space
and around the trough M, keeping the oil at or about the temperature of
the air in the casing E, above the division plate J. One of the many forms
of boiler which may be employed to utilize the caloric in the exhaust is

page_text: illustrated in Figure 4, where a plain vertical tubular boiler U, is shown
set in brickwork with a furnace beneath it, for a purpose to be explained
hereafter. The "exhausts" pass into a smoke box at the top of the boiler
through the passages Y, Y, which can be closed by the dampers therein
shown, and, after passing through the tubes, escape through the outlet w,
which is provided with a damper, the direction of the currents of the
exhausts being indicated by the arrows in solid lines. As this boiler may
be made available in starting the caloric engine, a fire to generate steam
may be kindled on the grates shown, and the dampers in Y and W closed,
when the draft will be in the direction indicated by the dotted arrows, escaping
past the damper vin the smoke outlet. The steam thus generated may be em-
ployed in an engine to work an air pump to compress air into the reservoir E,
and to support combustion on the grates c of the furnace within the casing,
or the engine which uses the steam may be coupled direct to the shaft R, to
rotate it, and thus compress air into E, and support combustion on grates c, by
After the fire is well
the action of the before described annular air pumps.
established on the grates c, and air compressed within E, the expansion by
heat of the compressed air, will work the caloric engine without any external
aid, and the fire kindled on the grates beneath U, may be permitted to die
out. The dampers in Y, when any are used, should be opened before the
shaft R is rotated, and the door of the furnace under the boiler and the
damper V, should at the same time be closed, while the damper in W, should
be opened. In small caloric engines constructed in accordance with my
Invention, and where the shaft R can be rotated by hand or otherwise
sufficiently to compress the air within E, it may be not worth while to attempt
to utilize the heat escaping in the exhaust, by applying it to generate steam,
but much may be utilized by increasing the area of the radiator G, which
may be entirely dispensed with when the boiler U is employed, substantially
as described.
In starting a fire on the grate c, the main inlet exhaust, and throttle valves,
and ash-pit door should be opened, and also the dampers in the exhaust exits
Y, so that the products of combustion may be carried off through the engine.
If the draft by this passage should be insufficient to make the fire burn freely,
then the valve e should be opened, and the door d taken off, thus establishing
a direct upward draft, which may be conducted by a temporary funnel. When
the fuel is well ignited, the doors J and d, the exhaust and main inlet valves,
.should be closed, and if the steam boiler is connected, the dampers should be
manipulated as before described. Air should then be supplied to the fire on

page_text: grates c, and compressed and expanded within E, by any of the means
mentioned, and by the fire on the grates, when sufficient pressure will be
generated to move and maintain in movement the pistons before referred to,
while the fire can be kept supplied with fuel by the described means. It
should be observed that the valve chest covers are provided with pipes T, as
shown in Figure 5, which extend up through the top of E, where the pipes
and the valve stems can be packed, without having the packing exposed to
heat that would be destructive to it.
In witness whereof, I, the said Philander Shaw, have heretofore set my
hand and seal, this Sixteenth day of January, in the year of our Lord
One thousand eight hundred and sixty-two.
PHILANDER SHAW. (L.S.)