IMPROVE-. MENTS IN HOT AIR ENGINES
Year: 1884

page_text: COMPLETE SPECIFICATION,
I LÉON BÉNIER of No 48 Rue du Ranelagh, Paris, in the Republic of France,
Civil Engineer do hereby declare the nature of my said invention for "IMPROVE-.
MENTS IN HOT AIR ENGINES" and in what manner the same is to be performed
to be particularly described and ascertained in and by the following statement:—
All hot air engines as hitherto constructed, considered with relation to the
heating of the air, consist of three distinct classes, whatever may be the mechanical
arrangements employed.
Firstly-Motors in which the air is heated in a vessel by an external furnace,
the heat being transmitted through the sides of the vessel which are presented to
the fire of the external furnace; the air is introduced and compressed in this vessel
by a pump and is introduced in a heated state into the cylinder in the same manner
as steam is introduced into steam engines.
Secondly-Motors in which air is compressed in a vessel as above described but
in which the air is heated by a furnace placed in the interior of the vessel the air
traversing the furnace and assisting the combustion.
Thirdly Motors in which the air is heated in the cylinder itself by a furnace"
placed outside the cylinder the heat being transmitted through the sides of the
cylinder which are exposed to the fire of the external furnace.
In this case the air enters the cylinder in a cold state whether it comes from a
vessel in which it has been compressed by a pump or whether it is introduced and
compressed in the cylinder by a pump or by the piston of the Motor.
These three methods of heating air are defective.
In motors of the first kind, in which air is heated in a vessel by an external
furnace, the air cannot be heated to a high temperature without injuring the sides
of the vessel which transmit the heat and the whole of the heat produced is not
transmitted to the vessel as a part of it escapes by the chimney.
In motors of the second kind, in which the air is heated by a furnace placed
within the vessel the two defects above mentioned are obviated, but the heat has
to be transmitted from the vessel to the cylinder and is consequently cooled, the
heated gases, before entering the cylinder, must pass through the distributing valve
which does not allow of their being utilized at a high temperature.
In motors of the third kind in which the air is heated in the cylinder by an
external furnace, the transmission of heat from the vessel to the cylinder and the,
passage of..the heated air through the distributing valve are avoided but owing to

page_text: the heat having to be transmitted through the metallic sides the temperature to
which the air can be raised is limited, frequent repairs become necessary and a
portion only of the heat produced can be utilized.
Now by my improvements the defects of the methods of heating air above
described are obviated.
In carrying out my invention I heat the air in the cylinder by a furnace placed
inside the cylinder, at each stroke of the piston air is introduced in a cold state into
the cylinder, either from a vessel in which it has been compressed or it may be
introduced directly by a pump or by the piston and pass through a furnace placed
in the cylinder and serve for the combustion.
The hot gases arising from the combustion greatly expanded by reason of their
high temperature drive the piston one stroke forward and are then expelled during
tho return stroke of the piston.
I would observe that in this hot air engine the method of heating the air is
somewhat similar to that employed for heating air in gas engines; in both cases
air is expanded by combustion within the cylinder but with this difference, namely,
that in gas engines the fuel (hydrogen, illuminating gas, carburetted air, and the
like) is introduced into the cylinder in a gaseous state whilst in the hot air motor,
the fuel (coke, coal, charcoal or other fuel) is introduced in a solid state.
A difficulty is met with as to the placing of a furnace within the cylinder the
hot gases filling the cylinder after traversing the furnace are charged with dust
and ashes and it becomes necessary to prevent the contact of this air charged with
ashes with the frictional surfaces of the cylinder and piston; this I effect in the
following manner.
In a vertical cylinder a open at its upper end and closed at its lower end by a
bottom cover o works a long piston b only that part of the cylinder from c to d
works air-tight within the cylinder the other and lower part d, f, is turned to a
diameter of about a millimeter smaller than the cylinder so as to leave between
the piston and the cylinder an annular space; the length d, f, of this annular space
is greater than the length of the stroke of the piston so that the bottom of the
piston cannot reach the surface of the cylinder against which the piston surface
slides the lowest limit of which is at m-Around the piston and in the annular
space d, f, whilst the hot gases are acting on the piston a current of air is made to
pass downward; the hot gases cannot enter the annular space around the piston
and consequently cannot come into contact with the frictional surfaces and therefore
cannot deposit any ashes thereon.
I will now describe a hot air engine constructed with a furnace in the interior of
the cylinder.
In this motor air is introduced and compressed at each stroke in the cylinder by
a pump.
In the drawing, figure 1 is a front view of a hot air engine constructed according
to my invention; figure 2 is a vertical section through the axis of the motor-
cylinder and figure 3 is a horizontal section through the axis of the pump cylinder.
The machine is constructed of a frame B resting on a base of stone work or of
cast iron. This frame B carries at its upper part two brackets in which oscillates
& beam D, each extremity of this beam carries a rod one of which connects it to
the piston and the other to the main shaft. The cylinder P, of the pump is
horizontal, open at one side, its piston H is governed by a rod jointed to the same
crank pin as the connecting rod; the motor cylinder a, is vertical bolted to the
back of the frame and serves for the bottom of the pump cylinder. The slide
valve t, serves to regulate the introduction of fresh air into the pump and the
forcing of this air into the motor cylinder; this slide valve may be replaced by
a suction valve and a delivery valve.
The slide valve is so regulated as to put the pump in communication with the
outside air during the exhaust, the crank pin describing the angle c, d, a', the air
entering by the orifice V and the duct q; During the forcing (arc a², b¹, c³) the
slide valve puts the pump in communication with the motor cylinder a. In the

page_text: motor cylinder the heated gases escape when the piston descends during the time
the crank pin is describing the arc d', a', b¹, when the forcing of the pump
commences, the escape valve 8, is open and fresh air, flows back through the pump
and escapes by this valve with the hot gases until the escape valve 8, is closed. The
piston being at the bottom of its stroke the valve is closed; before closing only
fresh air coming from the pump has passed as at this moment the speed of the
pump piston is at its maximum and that of the motor piston is nil the valve 8, has
thus been cleaned and cooled by the fresh air.
The valves, being closed, the fresh air which is still being forced in by the pump
can no longer escape outside and is forced back in the cylinder. The air enters the
cylinder by the ducts n, and p. The small quantity which passes through n, enters
the circular chamber m, and passes all round the piston and prevents the hot gases
from filling the annular space between the piston and the cylinder. The largest
portion of the air is brought under the grate g, by the duct p. This air passes
through the furnace h, burning the fuel; the gases arising from the combustion
attain a volume four to five times greater than that of the air introduced. The
pressure in the cylinder is constantly increasing so long as the pump forces in fresh
air; at c, the pump piston being at the end of its stroke the slide valve closes the
communication between the pump and the cylinder and the motor piston continues
to be impelled by the expansion of the hot gases. Figure 4, shows the indicated
work of the motive piston (Surface N) and the indicated work of the pump piston
(Surface M) the work which can be utilized being the difference between the two,
less the friction of the machine.
The motive piston having arrived at the end of its upward stroke the escape
valve 8, is raised and the hot gases escape outside during the descent of the piston ;
these heated gases are driven out by the piston, again pass through the furnace and
the grate g, and are expelled through the duct p, drawing with them the ashes.
If instead of an ordinary grate, a grate g, formed of superposed wire gauze be
employed the wire gauze will become heated by contact with the hot gases during
their escape and will heat the fresh air on its entry to the furnace thus obtaining
a higher temperature and consequently a greater expansion.
The introduction of the fuel is effected through the cock R. The cavity ml, of
this cock is filled when the cock is in the position shewn at figure 1; by then
turning the cock the fuel is caused to fall into the cylinder by the duct n¹. The
small hole x, closed by a glass plate allows of the furnace being inspected. The
fuel introduced should be of good quality and should not contain non-combustible
matters which would clog the furnace.
Each day, before the motor is put in action the bottom of the cylinder can be
raised in order to clear the grate.
In order to start the motor the fuel is introduced ready lighted on the grate and
a turn given to the fly wheel.
To prevent the lower part of the cylinder, in contact with the heated gases,
attaining too great a temperature this part of the cylinder can be isolated by lining
the interior thereof with a non conductor of heat; or the sides can be cooled by
causing a small current of cold water to circulate all round the cylinder as in gas
engines.
To regulate the working it is only necessary to employ a centrifugal regulator
which keeps the escape valve 8, raised when the normal rate of speed is passed; the
action of the motor being stopped when the escape valve is raised.
The cylinder a, with its piston b, and its. internal furnace h, being given, it is
obvious that the other parts of the machine may be modified in several ways; the
position of the pump can be varied, or a vessel may be employed into which the
fresh air is forced by a pump and afterwards introduced into the motor cylinder
during one portion of the stroke, the pressure in the cylinder being the pressure of
the vessel during the introduction. The pump and the vessel could be dispensed
with and the motor cylinder alone be retained thus not producing more than one
motive action every two turns of the shaft as in the "Otto" gas engine. In this

page_text: case the fresh air circulating around the piston should be furnished by a small pump
of special construction, the duct p, should open into the cylinder above the furnace ;
fresh air entering by the escape valve 8, would fill the cylinder during the exhaustion
and would be forced into a chamber under the grate during compression-the escape
of the hot gases and the introduction of fresh air take place through the same
valve 8. After this valve is the duct having two automatic valves, one for
exhausting cold air the other for forcing in hot air, the valve 8, would be well
cleaned before it is closed by a current of fresh air.
It will be easily seen that nothing would be changed from the principle of
heating air by a furnace placed in the interior of the cylinder by placing this
furnace not in the cylinder as shewn in figure 2, but in a chamber at the side of
the cylinder, the interior of this chamber and the cylinder being in constant
communication by a duct.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is:
(1) In a hot air engine the method of heating air by means of a furnace placed
in the interior of the cylinder whatever may be the mechanical arrangements
employed.
(2) In a hot air engine the arrangement of parts having for object to prevent
the contact of the hot gases with the frictional surfaces of the cylinder and of the
piston and thus allowing the introduction into the cylinder of hot gases charged
with dust and ashes.

page_text: This Specification was, upon the 11th day of March 1892, Amended under
Sections 18 to 21 of the Patents, Designs, and Trade Marks Act, 1883.
COMPLETE SPECIFICATION (AMENDED).
I LÉON BENTER of No 18 Rue du Ranelagh, Paris, in the Republic of France,
Civil Engineer do hereby declare the nature of my said invention for "IMPROVE-
MENTS IN HOT AIR ENGINES" and in what manner the same is to be performed
to be particularly described and ascertained in and by the following statement :-
All hot air engines as hitherto constructed, considered with relation to the
hoating of the air, consist of three distinct classes, whatever may be the mechanical
arrangements employed.
Firstly Motors in which the air is heated in a vessel by an external furnace,
the heat being transmitted through the sides of the vessel which are presented to
the fire of the external furnace; the air is introduced and compressed in this vessel
by a pump and is introduced in a heated state into the cylinder in the same manner
as steam is introduced into steam engines.
Secondly Motors in which air is compressed in a vessel as above described but
in which the air is heated by a furnace placed in the interior of the vessel the air
traversing the furnace and assisting the combustion.
Thirdly Motors in which the air is heated in the cylinder itself by a furnace
placed outside the cylinder the heat being transmitted through the sides of the
cylinder which are exposed to the fire of the external furnace.
In this case the air enters the cylinder in a cold state whether it comes from a
vessel in which it has been compressed by a pump or whether it is introduced and
compressed in the cylinder by a pump or by the piston of the Motor.
These three methods of heating air are defective.
In motors of the first kind, in which air is heated in a vessel by an external
furnace, the air cannot be heated to a high temperature without injuring the sides
of the vessel which transmit the heat and the whole of the heat produced is not
transmitted to the vessel as a part of it escapes by the chimney.
In motors of the second kind, in which the air is heated by a furnace placed
within the vessel the two defects above mentioned are obviated, but the heat has

page_text: to be transmitted from the vessel to the cylinder and is consequently cooled, the
heated gases, before entering the cylinder, must pass through the distributing valve
which does not allow of their being utilized at a high temperature.
In motors of the third kind in which the air is heated in the cylinder by an
external furnace, the transmission of heat from the vessel to the cylinder and the
passage of the heated air through the distributing valve are avoided but owing to
the heat having to be transmitted through the metallic sides the temperature to
which the air can be raised is limited, frequent repairs become necessary and a
portion only of the heat produced can be utilized.
Now by my improvements the defects of the methods of heating air above
described are obviated.
In carrying out my invention 1 heat the air in the cylinder by a furnace placed
inside the cylinder, at each stroke of the piston air is introduced in a cold state into
the cylinder, either from a vessel in which it has been compressed or it may be
introduced directly by a pump or by the piston and pass through a furnace placed
in the cylinder and serve for the combustion.
The hot gases arising from the combustion greatly expanded by reason of their
high temperature drive the piston one stroke forward and are then expelled during
the return stroke of the piston.
I would observe that in this hot air engine the method of heating the air is
somewhat similar to that employed for heating air in gas engines; in both cases
air is expanded by combustion within the cylinder but with this difference, namely,
that in gas engines the fuel (hydrogen, illuminating gas, carburetted air, and the
like) is introduced into the cylinder in a gaseous state whilst in the hot air motor,
the fuel (coke, coal, charcoal or other fuel) is introduced in a solid state.
A difficulty is met with as to the placing of a furnace within the cylinder the
hot gases filling the cylinder after traversing the furnace are charged with dust
and ashes and it becomes necessary to prevent the contact of this air charged with
ashes with the frictional surfaces of the cylinder and piston; this I effect in the
following manner.
In a vertical cylinder a open at its upper end and closed at its lower end by a
bottom cover o works a long piston only that part of the cylinder piston from c
to d works air-tight within the cylinder the other and lower part d, f, is turned to a
diameter of about a millimetor smaller than the cylinder so as to leave between
the piston and the cylinder an annular space; the length d, f, of this annular space
is greater than the length of the stroke of the piston so that the bottom of the
piston cannot reach the surface of the cylinder against which the piston surface
slides the lowest limit of which is at m― Around the piston and in the annular
space d,, whilst the hot gases are acting on the piston à current of air is made to
pass downward; the hot gases cannot enter the annular space around the piston
and consequently cannot come into contact with the frictional surfaces and therefore
cannot deposit any ashes thereon.
I will now describo a hot air engine constructed with a furnace in the interior of
the cylinder.
In this motor air is introduced and compressed at each stroke in the cylinder by
a pump.
In the drawing, figure 1 is a front view of a hot air engine constructed according
to my invention; figure z is a vertical section through the axis of the motor-
cylinder and figure 3 is a horizontal section through the axis of the pump cylinder.
The machine is constructed of a frame B resting on a base of stone work or of
cast iron. This frame B carries at its upper part two brackets in which oscillates
a beam D, each extremity of this beam carries a rod one of which connects it to
the piston and the other to the main shaft. The cylinder P, of the pump is
horizontal, open at one side, its piston H is governed by a rod jointed to the same
crank pin as the connecting rod; the motor cylinder a, is vertical bolted to the
back of the frame and serves for the bottom corer of the pump cylinder. The slide
valve t, serves to regulate the introduction of fresh air into the pump and the

page_text: forcing of this air into the motor cylinder; this slide valve may be replaced uy
a suction valve and a delivery valve.
The slide valve is so regulated as to put the pump in communication with the
outside air during the exhaust, the crank pin describing the angle c', d', a', the air
entering by the orifice V and the duct 7; During the forcing (arc a', b', c',) the
In the
slide valve puts the pump in communication with the motor cylinder a.
motor cylinder the heated gases escape when the piston descends during the time
the crank pin is describing the arc d', a¹, b. When the forcing of the pump
commences, the escape valve s, is
and fresh air flows back through forced
open
back by the pump and escapes by this valve with the hot gases until the escape
valves, is closed. The piston being at the bottom of its stroke the valve is closed;
before closing only fresh air coming from the pump has passed as at this moment
the speed of the pump piston is at its maximum and that of the motor piston is nil
the valve has thus been cleaned and cooled by the fresh air.
The valves, being closed, the fresh air which is still being forced in by the pump
can no longer escape outside and is forced back in the cylinder. The air enters the
cylinder by the ducks n, and p. The small quantity which passes through n, enters
the circular chamber m, and passes all round the piston and prevents the hot gases
from filling the annular space between the piston and the cylinder. The largest
portion of the air is brought under the grate y, by the duck p. This air passes
through the furnace h, burning the fuel; the gases arising from the combustion
attain a volume four to five times greater than that of the air introduced. The
pressure in the cylinder is constantly increasing so long as the pump forces in fresh
air; at c, the pump piston being at the end of its stroke the slide valve closes the
communication between the pump and the cylinder and the motor piston continues
to be impelled by the expansion of the hot gases. Figure 4, shews the indicated
work of the motive motor piston (Surface N) and the indicated work of the pump
piston (Surface M) the work which can be utilized being the difference between the
two, less the friction of the machine.
The motive motor piston having arrived at the end of its upward stroke the escape
valves, is raised by a tappet operated, by means of a rod, from the crank shaft and the
hot gases escape outside during the descent of the piston; these heated gases are
driven out by the piston, again pass through the furnace and the grate g, and are
expelled through the duct p, drawing with them the ashes.
If instead of an ordinary grate, a grate g, formed of superposed wire gauze be
employed the wire gauze will become heated by contact with the hot gases during
their escape and will heat the fresh air on its entry to the furnace thus obtaining
a higher temperature and consequently a greater expansion.
The
The introduction of the fuel is effected through the cock R. The cavity m³, of
this cock is filled when the cock is in the position shewn at figure 1; by then
turning the cock the fuel is caused to fall into the cylinder by the duct n.
small hole x, closed by a sight glass, plate allows of the furnace being inspected. The
fuel introduced should be of good quality and should not contain non-combustible
matters which would clog the furnace.
Each day, before the motor is put in action the bottom of the cylinder can be
raised in order to clear the grate.
In order to start the motor the fuel is introduced ready lighted on the grate and
a turn given to the fly wheel.
To prevent the lower part of the cylinder, in contact with the heated gases,
attaining too great a temperature this part of the cylinder can be isolated by lining
the interior thereof with a non conductor of heat; or the sides can be cooled by
causing a small current of cold water to circulate all round the cylinder as in gas
engines.
To regulate the working it is only necessary to employ a centrifugal regulator
governor which keeps the escape valves, raised when the normal rate of speed is
passed; the action of the motor being stopped when the escape valve is raised.
The cylinder a, with its piston b, and its internal furnace h, being given, it is

page_text: obvious that the other parts of the machine may be modified in several ways; the
position of the pump can be varied, or a vessel may be employed into which the
fresh air is forced by a pump and afterwards introduced into the motor cylinder
during one portion of the stroke, the pressure in the cylinder being the pressure of
the vessel during the introduction. The pump and the vessel could be dispensed
with and the motor cylinder alone be retained thus not producing more than one
motive action every two turns of the shaft as in the "Otto" gas engine. In this
case the fresh air circulating around the piston should be furnished by a small pump
of special construction, the duct p, should open into the cylinder above the furnace;
fresh air entering by the escapo valve s, would fill the cylinder during the exhaustion
and would be forced into a chamber under the grate during compression-the escape
of the hot gases and the introduction of fresh air take place through the same
valve s. After this valve is the duet having two automatic valves, one for
exhausting cold air the other for forcing in hot air, the valve-s, would be well
eleaned before it is closed by n enrrent of fresh air. In combination with this valve
is a conduit or duct hacing two automatic valves through one of which cold air is
exhausted and through the other hot air is forced so as to ensure the cleansing of the
valve s, by a current of fresh air.
It will be easily seen that nothing would be changed from the principle of
heating air by a furnace placed in the interior of the cylinder by placing this
furnace not in the cylinder as shewn in figure 2, but in a chamber at the side of
the cylinder, the interior of this chamber and the cylinder being in constant
communication by a duct.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is:
(1) In a hot-air engine the method of heating air by means of a furnace placed
the interion of the aulindon hotovos new he the