Improvements in Hot Air Engines.
Year: 1892

page_text: ”
Date of Application, 23rd Nov., 1892
Complete Specification Left, 18th Sept., 1893-Accepted, 21st Oct., 1893
PROVISIONAL SPECIFICATION.
Improvements in Hot Air Engines.
I, HENRY MARIE LÉON CROUAN, Engineer, of 14, Rue Fromentin, Paris, in
the Republic of France, do hereby declare the nature of this invention to be as
follows:
The engine which forms the subject of the present invention differs from previous
ones in having no pump.
It may work either with or without preliminary compression. In the latter case
the air is heated, its volume remaining the same, after having been drawn in at atmo-
spheric pressure; in the other case the air drawn in at atmospheric pressure is
raised to a higher pressure before being heated, by the introduction or forcing back
into the space which it occupies, of a certain quantity of the gases produced by
combustion during the previous stroke; .this forcing back being effected by the
main piston.
The said gases may be cooled before being forced back, or they may be delivered
without cooling into the compression chamber.
The main piston, cylinder, connecting rod, and other parts are similar to those
used in most gas engines.
A vertical cylinder arranged at the outer end of the principal cylinder is closed
below by a cup shaped cover, lined with refractory material and having an opening
at the bottom fitted with a grate.
In the vertical cylinder works a piston or diaphragm at the lower end of a tube
which passes through a stuffing box and is operated by the mechanism hereinafter
described.
The cover of the cylinder enters for a considerable distance into the latter
leaving a space between them into which the vertical edge of the piston rises. It
is provided with an inlet valve and in its lowest position it closes an opening which
communicates with the horizontal main cylinder. In its highest position, when it
surrounds the part of the cover which enters the cylinder, an opening in the side of
the tube which drives it is opposite to an oblique passage provided with a valve
which can be actuated by a lever.
In the walls of the cylinder are two openings, each communicating with a vertical
passage the lower ends of which enter an annular groove between the lower flange
of the cylinder and the cup-shaped cover which closes it.
This groove communicates, on the one hand with a certain number of small openings
leading to the interior of the cylinder, some of which openings may be partially or
entirely closed by screws, and on the other hand with a space between the refractory
lining and the cover, or below the grating. A door in the side of the cylinder,
which can be closed by a screw, allows the cleaning and lighting of the fuel, and an
eye-piece in the door allows the operation to be watched when the engine is working.
The opening at the bottom of the lower cover is also closed by a screw door.
Supposing the piston to be at the top of its stroke and the main piston at the
outer end of its stroke, during the dead point of the latter the first piston is made
to descend and to drive out the burned gases to a chimney by an opening in the
back end of the main cylinder, and at the same time to draw in air by the suction
valve already described which at this moment has been released, by a cam, from a
lever which keeps it closed. Even without a valve very little of the hot gases
would mix with the air drawing in, since on the one hand the pure entering air meets
with scarcely any resistance in passing through the suction passage and on the other

page_text: hand the gases below the piston would have to overcome a considerable resistance
in order to pass up, whilst traversing the fuel, the grate, and the passages. Valves
however may be added if thought advisable.
The piston is now at the bottom of its stroke, and above it nearly pure air,
whilst the main piston is still near the outer end of its stroke. The vertical piston
does not move during the back stroke of the main piston.
If the engine is to work without compression, the gases in the interior of
the main cylinder escape through the exhaust valve during the back stroke of
the piston.
If it is to work with compression, the exhaust is closed at the beginning of, or
during, the back stroke and the main piston forces back the gases above the
vertical piston through small holes pierced through the upper edge of the walls of
the latter. When the main piston has arrived at or near the back end of its stroke,
the vertical piston is made to rise sharply. The air and the gas (if any is present)
are forced back into the annular groove already described whence they pass into
the cylinder partly through the small opening in the walls of the latter and partly
through the grate and fire. The air passing through the small openings described
is intended to burn, as it leaves the fire, the carbonic oxide produced by the passage of
the gases already previously burned and forced back into the fire by the main piston.
After this operation the vertical piston is at the top of its stroke, the main piston
at the back end of its stroke, and the air and gases, relatively cold and previously
above the vertical piston, are now below the latter and have been highly heated without
their volume being changed. Their pressure is therefore much greater, and they
drive the main piston forward, whilst the vertical piston does not move. At the
end of the stroke the exhaust opens and the series of operations recommences
whilst the piston makes its back stroke.
If it is intended to cool the burned gases before forcing them back into the
vertical cylinder, instead of sending them back whilst still very hot, a series of
openings are made round the main cylinder near its front end, which are uncovered
by the main piston before it arrives at the outer end of its stroke, and before the
exhaust valve is opened. These openings lead into an annular passage commu-
nicating with a cooling vessel between which and the cylinder an equilibrium of
pressure is established, a large part of the hot gases entering the cooling vessel
through a valve. The pressure will however be above that of the atmosphere and
when the exhaust valve opens, the gases in the cooling vessel will close by their
pressure the valve through which they entered, and after passing through the
cooling vessel will return to the cylinder through another valve, driving before them
the hot gases still in the cylinder which will pass through the exhaust valve,
leaving the cylinder filled with the cooled gases.
These latter gases have been cooled whilst passing in the cooling vessel through
a layer of porous or spongy material placed between two gratings, by means of the
cooling water from a jacket round the main cylinder, which entering the jacket at
one opening passes off in the usual way through another opening, from whence it
enters the cooling vessel. The construction of this cooling vessel may evidently
be varied more or less.
The valve in the oblique passage in the cover of the vertical cylinder already
described is provided with a recess into which, when the valve is in one position, a
piece of charcoal or other fuel is admitted from a hopper, whilst in its other
position such piece passes down through the opening in the tubular rod of the
vertical piston and down the latter into the fire. The valve is actuated by a ratchet
and pall driven by the gear which works the vertical piston.
The following is the method in which the different parts of the engine are
actuated :-
A disc is fixed upon the end of the main shaft of the engine and is provided with
cams which operate the exhaust and suction valves already described, and it also is
provided with a crank pin fitted with a connecting rod the other end of which is
forked and is compelled to move in the are of a circle by being pivotted to the end

page_text: of a short radius link, and its forked end embraces a pivotted ring which slides upon
an arm operating in the following manner. At the beginning and at the end of the
curve described by the forked end of the connecting rod the movement of the bar
upon which the ring slides will be slight, whilst at the centre of the stroke the ring
sliding on the arm will be brought close to the centre upon which the upper end of
the said bar oscillates, and the movement of its other end will be considerably
quicker than that of the forked end and ring which actuate it and which are then
near to its upper end as described.
This movement combined with that of the connecting rod, the other end of which
describes a circle, causes a small amount of movement at the dead points and a
considerably greater movement at the intermediate points, whilst the movement of
the pivotted bar is much slower still at the said dead point and quicker at the
intermediate ones, and in fact the movement approaches to an intermittent one..
This effect may be increased by a repetition of the same arrangement, a
connecting rod driven by the lower end of the pivotted bar described, being forked
at its outer end, which is pivotted to a radius link and also carries a pivotted ring
sliding upon a pivotted bar in a way similar to that already described. The
movement of this last bar is practically entirely intermittent, so slow is it rendered
at the dead points and so much faster at the intermediate ones. An arm or lever
fixed upon the same centre as that upon which it turns, so as to form a bell crank,
is connected to a rod the other end of which is pirotted to levers by whic!
the required movement is given to the vertical piston already described, and
to the ratchet which actuates the device already described through which
the fuel is intermittently supplied. By adjusting the position of the joint
upon the bell crank the length of stroke of the vertical piston may be varied.
The double combination described ensures an almost complete stoppage of the
vertical piston during the in and out stroke of the main piston, and an extremely
rapid movement and sudden stop of the former during the passage of the latter
past its dead points, it having moved through a very small arc of a circle during
the movement of the vertical piston.
The arrangement described produces a result approaching theoretical perfection,
but in order to simplify the apparatus the second set of levers described may be
omitted, the valve and vertical piston being driven by a lever actuated by the first
set only. Or still greater simplicity may be obtained by driving the piston and
valve direct by a connecting rod arranged at an angle of about 90 degrees with the
main connecting rod of the engine, but in this case the result obtained is not nearly
so good, the movement of the main piston during the rise or fall of the vertical
piston being considerable.
The governing of the engine effected by throttling the supply of gases to the
fire when the movement is too quick.
Air and gas drawn in and forced back are discharged into a chimney or the open
air. For this purpose it is sufficient that the suction valve should not close, the
vertical piston in rising discharging the gases above it.
It has already been mentioned that the suction valve is actuated by a cam. A.
spring tends constantly to raise an arm which acts upon a cap upon the spindle of
the valve aud keeps the latter pressed in its seat. When the cam acts the
valve is disengaged and falls by its own weight allowing the air to enter without
resistance.
When the engine is working properly an oscillating weight mounted upon the
rod actuated by the cam and following its movement engages at each stroke, by the
intervention of a steel spring which it carries, a catch actuating a pall mounted
upon the same axis. The pall is therefore lowered at each stroke but has no other
action. If however the speed increases, the weight will hang behind and the pall
will engage in a notch in a lever connected with that which raises the valve and
holds it in its place, and this lever being held back the valve will remain lowered.
As the vertical piston rises, therefore, the air and gas will be discharged back
through the valve. At the next stroke, or when the speed has become normal, the

page_text: pall will be disengaged from the lever and the valve will be closed, so that the
working of the engine resumes its proper course.
In this engine therefore there is no pump compressing the air, or subject
during the stroke in the main piston to any pressure upon one side of its piston
only. The vertical piston described in no way acts as a pump, but only serves
to act upon the air and gases in the manner and for the purposes described,
and the only difference in pressure on its two sides is that arising from the
resistance to their movement through the passages. Whilst the main piston is
working the vertical one does not move, but when the former has arrived at
its: inner dead point the vertical piston passes the gases from above to below
across the fuel or through the openings for the purpose, but here again the only
difference of pressure on the two sides arises from the resistance of the air or
gas passing through the channels or through the fuel, the upper and lower sides
of the piston being in communication.
In fact at any particular moment, if a sudden stoppage be assumed, an
equilibrium of pressure would be exactly established above and below the
vertical piston, and in any case this equilibrium is only varied by the unavoid-
able resistance in the passages, that is to say to a very slight extent which is
diminished as much as possible by reducing the resistance.
The cycle of movements of the engine is as follows:
1st. With compression. 1. Suction of pure air by the vertical piston during
the front dead point of the main piston. 2. Compression of this air by forcing
back the burned gases, cooled if desired, by the main piston to the top of the
vertical piston. 3. The heating of the air the volume of which remains unaltered,
by the movement of the vertical piston during the back dead point of the main
piston. 4. Utilization of the heated air by. the main piston whilst the vertical
piston remains unmoved. 5. Shortly before the outstroke, cooling the burned
gases by the water passing from the jacket of the main cylinder or by other
means (such as fresh cold water used directly,) and cleaning out from the
cylinder the still hot gases by means of the cooled gases, whatever may be
the means employed for cooling them, (water or even atmospheric air in case
of need).
If compression is not used, the first, third, and fourth steps of the cycle are
used, only.
EDWARDS & Co.,
35, Southampton Buildings, London, Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in Hot Air Engines.
I, HENRY MARIE LÉON CROUAN, Engineer, of 14 Rue Fromentin, Paris, in 4
the Republic of France, do hereby declare the nature of this invention and
in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement and accompanying drawings, that is
to say :-
The engine which forms the subject of the present invention differs from previous 4
ones in having no pump. It may work either with or without preliminary com-
pression. In the latter case the air is heated, its volume remaining constant, after
having been drawn in at atmospheric pressure; in the other case the air drawn in
at atmospheric pressure is raised to a higher pressure before being heated, by the
introduction or forcing back into the space which it occupies, of a certain quantity 5
of the gases produced by combustion during the previous stroke, this forcing back
being effected by the main piston.
The said gases may be cooled before being forced back, or they may be delivered
without cooling into the compression chamber.
1

page_text: The main piston, cylinder, connecting rod, and other parts, are similar to those
used in most gas engines, and it is unnecessary therefore to describe them
particularly, the following description being confined to the novel parts and
combinations which form the subject of the invention.
The accompanying drawings are in illustration of my invention.
Figure 1 is a side view, and Figure 2 a plan, of an engine.
Figure 3 is a longitudinal section of the working parts upon a somewhat smaller
scale.
A vertical cylinder A arranged at the outer end of the principal cylinder B,
Figure 3, is closed below by a cup shaped cover C lined with refractory material B,
and having an opening below fitted with a grate E. The lining D may be replaced
by a conical grating.
In the cylinder A works a piston or diaphragm F, at the lower extremity of the
tube G which passes through a stuffing box and is operated by the mechanism
hereinafter described. The cover of the cylinder A enters for a considerable
distance into the latter, and is provided with a valve H (shewn in dotted lines)
which serves as an admission valve. The diaphragm in its lowest position closes
the communication with the principal cylinder.
At the upper part of its stroke, when it surrounds the part of the cover which
enters the cylinder, a lateral opening a in the side of the tube is opposite to an
oblique passage b communicating with a feeding device or valve through which fuel
is supplied.
In the sides of the cylinder are two openings (of which only one is seen in
Figure 3, the other being opposite to it) each opening into a vertical passage
(shewn in dotted lines) communicating with a circular recess J. This recess or
groove communicates on the one hand with the interior of the cylinder by means of
a number of openings o, o, some of which may be partially or entirely closed by
sorowe from the outside as shewn in Figure 1, and on the other hand with the outer
side of the lining D or of the grating which may replace it as already explained,
neither of which touches the cover C.
A door K, which can be fixed by a screw, allows the cleaning of the grate and
lighting of the fuel, and an eye piece M allows the operation to be watched when
the engine is working. The opening at the bottom of the lower cover is closed by
a door L, fixed by a screw and allowing the fire place to be cleaned.
Supposing the diaphragm to be at the top of its stroke and the main piston at
the outer end of its stroke, during the dead point of the latter the mechanism
hereinafter described forces the diaphragm down which drives back the burned
gases to a chimney through an exhaust valve N and at the same time draws in air
by the valve H, which at this moment is disengaged by the action of a cam from a
lever which normally keeps it closed. The opening I even without a valve would
only allow very little of the hot gases to be drawn in, since on the one hand the
fresh air meets with scarcely any resistance in entering through the large open
valve H, and on the other hand the gases situated below the diaphragm would have
to overcome considerable resistance in travelling up whilst passing through the
fuel, the grate, and the different passages. If desired, however, for greater safety
the openings I may be provided with valves which need not however be perfectly
tight, so that in case of need they may be passed by.
The diaphragm is now at the bottom of its stroke, and above it nearly pure air,
whilst the main or motor piston is still near the outer end of its stroke. The
diaphragm or vertical piston does not move during the back stroke of the main
piston.
If the engine is to work without compression, the expanded gases escape through
the exhaust valve during the whole of the back stroke of the piston. If it is to
work with compression, the exhaust valve is closed at the beginning of, or during,
the back stroke, and the main piston forces the gases back above the diaphragm
piston through the small holes s in the side of the latter.
When the main piston has arrived at or near the back end of its stroke the

page_text: diaphragm piston is made to rise sharply. The air and the gas (if any is at present)
are forced back through the openings I into the annular recess or groove J whence
they pass into the cylinder, partly through the openings o and partly through the
fire-grate, (or the grating, if the lining is not of fireclay).
The air passing through the openings » serves to burn, as it leaves the fire-place,
the carbonic oxide produced by the passage of the gases, previously burned and
forced back by the main piston into the fireplace.
After this operation the diaphragm is at the top of its stroke, the main piston at
the back end of its stroke, and the relatively cold air and gases which were
previously above the diaphragm are now below it and have been highly heated
without their volume being changed.
Their pressure is therefore much greater and they drive the main piston forward
whilst the diaphragm piston is held back and does not move. At the end of the
stroke the exhaust valve is opened and the series of operations recommences whilst
the main piston makes its back stroke.
If it is desired to cool the burned gases before forcing them back into the
cylinder A. instead of forcing them back whilst still hot, a series of openings at
is provided which the main piston uncovers before it reaches the outer end of its
stroke and before the exhaust valve is opened.
Through these openings and the annular passage 9 an equilibrium of pressure
will be established between the cylinder and the cooling vessel P, a large part of
the hot gases passing into the vessel P through the valve c¹.
The total pressure will however be above that of the atmosphere, and when the
exhaust valve opens, the gases under such pressure in P will open the valve c and
passing back through will sweep out before them the hot gases which are still in
the cylinder, driving them out through the exhaust valve and leaving the cylinder
-filled with the cooled gases.
These gases will be relatively cool, as they will have passed in P a layer of
porous or spongy material placed between two gratings and constantly damped by
the cooling water in the jacket of the main cylinder which entering at Q leaves
at R and enters P through the rose T. In Figure 3 this arrangement is shewn in
such a manner as to make it more readily understood. The cooling vessel shewn
in the elevation (Figure 1) although identical in principle would have required
more drawings, as the several openings could not have been shewn on the same
plan. A valve R (provided with a ball or float if preferred,) allows the surplus
water to escape.
The fuel is supplied through the tube G when the diaphragm piston is at the
-top of its stroke. The chamber or cock which is operated at intervals will have
discharged a piece of coal or fuel into the passage b, and when the tube reaches
the top of its stroke the opening a uncovers the passage b and the piece of fuel
falls between the tube into the fire. The diaphragm piston is bevelled so as not.
to cover the openings I until it has finished its stroke.
The feeding valve or device is operated by means of a ratchet wheel and pall
driven by the gear which works the diaphragm piston.
The devices for operating the several parts are specially designed for the
purpose. A crank disc is fixed upon the end of the main shaft and carries cams
which operate the escape valve and the inlet valve as already mentioned, and a
crank pin upon it drives at the same time a small connecting rod the forked end d
of which (Figure 1) is compelled to describe a curve round the centre y by means
of the oscillating lever e and also operates a ring which slides upon the arm f.
At the beginning and at the end of the arc through which the point d moves the
movement of the arm fround the centre will be slight. At half stroke, on the
other hand, the sliding ring will have been brought close to the point z on which
the lever turns, and the movement of the outer end off will consequently be very
much quicker than that of the fork d which operates upon f very close to the axis
of rotation of the latter.
It will be observed that this movement is combined with that of the connecting

page_text: rod, which describes a circle at its other end so that it causes little movement at.
its outer end at the ends of its stroke and much more at the intermediate part,
and that therefore the movement which actuates fis much slower at the ends of
or dead points of the stroke, and much quicker at or near the middle so that a
practically intermittent movement is obtained by the simple sliding arrangement.
The desired effect may be obtained even more perfectly by a double sliding
movement, the second being substantially a repetition of the first, the connecting
rod g driven by the lever f driving by its forked end h, (which is compelled by
the lever turning upon the centre to describe a curved path), operating a
ring which slides upon the lever or bar j. The movement of round its
centre wis practically now intermittent, its movement being so much reduced at
the dead points and increased at the intermediate one. The arm K of the
lever drives the connecting rod which by means of the levers m and n give
the required movement to the diaphragm piston, and by the lever p to the fuel.
supplying device or valve.
The ring fixed by a set screw upon the lever K allows the length of stroke-
of the diaphragm piston to be varied. The combination of the double sliding
movements described produces an almost complete pause of the diaphragm piston
during the backward and forward strokes of the main piston and an extremely
rapid rise and stop of the latter during the passage of the main piston through.
the ends of its stroke or the dead points of the crank, the latter during this.
rise having passed through a very short arc of a circle.
Although the mechanism described is the most theoretically perfect it may be
considered somewhat complicated. By sacrificing a part of the efficiency to
simplicity, there part only of the actuating device may be used, the second part
being omitted and the point being driven directly by the crank pin. Or in.
cases where the greatest simplicity is necessary both the devices described may be
omitted and the rod 7 driven by a connecting rod fixed at an angle of about 90°
with the main connecting rod of the engine, but this simplification is detrimental
to the effective working, the heating not taking place whilst the volume remains.
constant or nearly so, as the movement of the main piston during the rise and:
fall of the diaphragm piston will be considerable.
The governing of the engine is effected by cutting off the supply of gases to the
fire when the movement is too quick. The air and gas drawn in and forced back
are discharged to the chimney or to the open air, and for this purpose it is only
necessary that the inlet valve should not be allowed to close and the diaphragm
in rising then discharges the gases above it into the open air.
It has been mentioned that the crank disc is provided with a cam operating by
connecting gear the inlet valve H. A spring V tends constantly to raise the
arm V₁ which presses upon the cap a upon the spindle of the valve H and presses.
the latter upon its seat (Figures 1 and 3).
When the cam comes into action the rod X pulling upon the arm Y of the
same lever disengages the valve H, which falls by its own weight and allows the
air to enter without resistance. If the action takes place normally a tumbling
weight Y¹ arranged at the end of X and moving with it engages at each move-
ment by means of a steel spring W which it carries, a piece W driving a pawl Si
mounted upon the same axis. The pall therefore is lowered at each stroke and
has no action. But if the speed increases the weight will at once hang back and
the spring raised by its movement will no longer come in contact with W and the
pall will engage with the notch at the foot of the arm Y. This arm and the
lever V¹ which are in one piece will therefore remain in their place when X begins.
to move back, and the valve H will remain open. When the diaphragm piston.
rises the air and gas will therefore. be discharged. At the next stroke, if the speed
has become normal, the steel blade or spring will engage with the piece which
releases the pall and the spring V will operate the lever which will close the.
valve.
}
If, on the other hand, the speed is still too quick, the steel blade will still.

page_text: remain disengaged and the arm Y will still be held, the arm B¹ lowered, and the
valve H opened.
In this engine, therefore, there is no pump for compressing the air or for
subjecting the displacing piston or pump to any pressure whatever upon one face
only when in operation. The diaphragm piston in no way takes the part of a
pump, except for the purpose of expelling the expanded gases into the air and of
drawing in gases at atmospheric pressure, and therefore the sole difference of the
pressure upon the two faces of the diaphragm piston can be only that caused by
the friction of the gases in the passages.
At other times whilst the main piston is moving the diaphragın piston does not
stir until the former has arrived at the end of its stroke. The diaphragm piston
passes the gases from above to below through the fuel, or upward through the
openings for the purpose, but in this case again the sole difference of pressure
arises from the resistance of the air or gases in moving through the passages or
through the fuel, the top and bottom. of the piston being in communication.
In short, at any point whatever of the stroke, if we suppose an instantaneous
stoppage, an exact equilibrium of pressure would be established above and below
the diaphragm piston, by means of the construction described, and in any case this
equilibrium is only destroyed by the action of the unavoidable friction in the
passages, that is to say to a very small extent indeed, which moreover will
be diminished as much as possible by diminishing the resistance and friction in
the passages.
The cycle of the engine is as follows, according as it works with or without
compression :-
Ieating the air whilst at a constant
volume by means of the diaphragm
piston during the back dead point of the
crank and piston.
Expansion of the heated air behind the
main piston whilst the diaphragm piston
remains at rest.
little before the end of the stroke, the
cooling of the burned gases by the
water from the cylinder jacket or by
other means (fresh cold water supplied
direct), and the sweeping out of the
still hot gases from the cylinder by such
cooled gases, whatever the means
employed for cooling them (water, or
even atmospheric air if necessary).
ascertained the nature of my said inven-
o be performed, I declare that what I
consisting of a vertical cylinder and a

page_text: horizontal cylinder, the communication between which is interrupted intermittently
by means of a diaphragm piston moving vertically, which also regulates the supply
of fuel to a fireplace and is driven, as well as an inlet valve for air and an exhaust
valve, by means of rods and levers actuated by a cam upon a crank disc carried by
the driving shaít of the engine, substantially in the manner and for the purposes
described and illustrated.
2. The device for cooling the hot gases, consisting of a cooling vessel containing
porous or spongy material and provided with inlet and outlet valves for the gases,
which are cooled by water admitted through a rose from the water jacket of the
main cylinder or from other source, arranged and operating substantially in the
manner described and illustrated.
3. The general arrangement of the parts of the engine, substantially as described
and illustrated.
Dated this 15th day of August 1893.
EDWARDS & Co.,
35, Southampton Buildings, London, Agents for the Applicant.