IMPROVE- MENTS IN HOT-AIR ENGINES
Year: 1860

page_text: LETTERS PATENT to John Henry Johnson, of 47, Lincoln's-Inn-Fields,
in the County of Middlesex, and of 166, Buchanan Street, in the City
of Glasgow, North Britain, Gentleman, for the Invention of "IMPROVE-
MENTS IN HOT-AIR ENGINES."-A communication from abroad by Stephen
Wilcox, the younger, of Westerley, in the County of Washington, in
the United States of America.
Sealed the 6th July 1860, and dated the 30th January 1860.
PROVISIONAL SPECIFICATION left by the said John Henry Johnson
at the Office of the Commissioners of Patents, with his Petition, on
the 30th January 1860.
I, JOHN HENRY JOHNSON, of 47, Lincoln's-Inn-Fields, in the County of
Middlesex, and of 166, Buchanan Street, in the City of Glasgow, North
Britain, Gentleman, do hereby declare the nature of the said Invention för
"IMPROVEMENTS IN HOT-AIR ENGINES," a communication from abroad' by
Stephen Wilcox, the younger, of Westerley, in the County of Washington, in
the United States of America, to be as follows:-
This Invention relates to the general construction and arrangement of hot-
air engines, whereby such prime movers are rendered more durable and
capable of working more rapidly and powerfully than heretofore.
The improvements consist, firstly, of a peculiar mode of arranging and com-
bining the pistons and means of effecting the induction and eduction of air in
the two cylinders, whereby one of the pistons serves as a means of changing

page_text: .
the air from the cold to the hot end of the cylinder, and also as a means of
supplying a fresh quantity of air to be used in the next stroke.
Secondly, in allowing the products of combustion to circulate in contact with
the ends of both the working cylinders and the changing cylinder, thereby
greatly increasing the amount of heating surface without involving loss of
space by the introduction of heating chambers or air passages.
Thirdly, in regulating the temperature of the heating surfaces by the employ-
ment of a chamber and diaphragm, so arranged relatively to the heating
surfaces and to the damper in the smoke flue (or valve for admitting air into
the furnace above the flue), that the rate of combustion in the furnace is
thereby regulated so as to maintain the surfaces at an even temperature.
Fourthly, in so constructing the regenerator that it shall gradually increase
in area from the cold to the hot side, whereby the resistance to the passage of
the air is rendered uniform.
Fifthly, in so constructing and operating a single valve in a chamber com
municating with the cylinders and the external air in combination with two
pistons, as herein-before referred to, that one valve performs the several offices
of an induction, eduction, and equilibrium valve.
Sixthly, in making the changing piston in two parts one above the other,
and while one portion of the air passes through the regenerator in the usual
manner, in its passage from the cold to the hot side of the double piston so
formed, compelling the other portion to traverse the space between the upper
and lower parts of the piston, in order to convey away by conduction the heat
which is conducted upwards through the lower part to the intermediate space.
By this means the upper portion of the piston; or that surface thereof which is
presented to the contact of the entering air, is maintained at a low tempera-
ture, and the air thereby drawn in with its full and proper volume.
Seventhly, in providing a cavity in the upper portion of the working piston,
which cavity is in free communication with the external atmosphere, and is
caused by the motion of the piston to change its contents in whole or in part
at each stroke, thereby carrying away the heat into the external atmosphere,
and preventing its accumulation at the rubbing parts.
Eighthly, in heating the air below the pistons by burning jets of gas or
vapour therein in lieu of applying heat to the exterior of the bottoms of the
cylinders.
Ninthly, in reducing or lowering the temperature of an engine acting by
internal combustion, by mingling other air at a lower temperature with the
products of combustion.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said John Henry Johnson in the Great Seal Patent Office on
the 30th July 1860.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, Jonn
HENRY JOHNSON, of 47, Lincoln's-Inn-Fields, in the County of Middlesex,
and of 166, Buchanan Street, in the City of Glasgow, North Britain, Gentle-
man, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Thirtieth day of January, in the year of our Lord
One thousand eight hundred and sixty, in the twenty-third year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto
me, the said John Henry Johnson, Her special license that I, the said
John Henry Johnson, my executors, administrators, and assigns, or such
others as I, the said John Henry Johnson, my executors, administrators,
or 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 Isle of Man, an
Invention for "IMPROVEMENTS IN HOT-AIR ENGINES," a communication from
abroad by Stephen Wilcox, the younger, of Westerley, in the County of
Washington, in the United States of America, upon the condition (amongst
others) that I, the said John Henry Johnson, 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 John Henry Johnson, do hereby
declare the nature of the said Invention, and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following.
statement, reference being had to the accompanying Drawings, to the letters.
and figures marked thereon, that is to say:-
The said Invention relates to the general construction and arrangement of
hot-air engines, whereby such prime movers are rendered more durable and
capable of working more rapidly and powerfully than heretofore. The improve-
ments consist, firstly, of a peculiar mode of arranging and combining the
pistons and means of effecting the induction and eduction of, air in the two
cylinders, whereby one of the pistons serves as a means of changing the air

page_text: from the cold to the hot end of the cylinder, and also as a means of supplying.
a fresh quantity of air to be used in the next stroke.
Secondly, in allowing the products of combustion to circulate in contact
with the ends of both the working cylinder and the changing cylinder, thereby
greatly increasing the amount of heating surface without involving loss of
space by the introduction of heating chambers or air passages.
Thirdly, in regulating the temperature of the heating surfaces by the employ-
ment of a chamber and diaphragm so arranged relatively to the heating surfaces
and to the damper in the smoke flue (or valve for admitting air into the furnace
above the flue), that the rate of combustion in the furnace is thereby regulated
so as to maintain the surfaces at an even temperature.
Fourthly, in so constructing the regenerator that it shall gradually increase
in area from the cold to the hot side, whereby the resistance to the passage of
the air is rendered uniform.
Fifthly, in so constructing and operating a single valve in a chamber com-
municating with the cylinders and the external air in combination with two
pistons, as herein-before referred to, that one valve performs the several offices
of an induction, eduction, and equilibrium valve.
manner,
Sixthly, in making the changing piston in two parts, one above the other,
and while one portion of the air passes through the regenerator, in the usual
in its passage from the cold to the hot side of the double piston so
formed, compelling the other portion to traverse the space between the upper
and lower parts of the piston, in order to convey away by conduction the heat
which is conducted upwards through the lower part to the intermediate
space. By these means the upper portion of the piston, or that surface
thereof which is presented to the contact of the entering air, is maintained.
àt a low temperature, and the air thereby drawn in with its full and proper
volume.
Seventhly, in providing a cavity in the upper portion of the working piston,
which cavity is in free communication with the external atmosphere, and is
caused by the motion of the piston to change its contents in whole or in part
at each stroke, thereby carrying away the heat to the external atmosphere and
preventing its accumulation at the rubbing parts.
Eighthly, in heating the air below the pistons by burning jets of gas or
vapour therein, in lieu of applying heat to the exterior of the bottoms of the
cylinders.
Ninthly, in reducing or lowering the temperature of an engine acting by
internal combustion by mingling other air at a lower temperature with the
Broducts of combustion.

page_text: And in order that the said Invention may be fully understood, I shall now
proceed more particularly to describe the same, and for that purpose I shall
refer to the several Figures on the Sheet of Drawings hereunto annexed, the
I same letters of reference indicating corresponding parts throughout all the
Figures.
Figure 1 of the annexed Sheet of Drawings represents a vertical section of
the improved hot-air engine; Figure 2 is a corresponding plan of the same;
Figure 3 is a horizontal section taken through the regenerator; Figure 4 is a
side valuation of the valve gear; Figure 5 is a plan of the same; Figures 6,
7, 8, 9, 10, 11, 12, and 13 are outline diagrams, shewing the position of the
pistons, and the valve at each eighth-part of the revolution of the crank; and
Figure 14 represents another mode of heating the air.
The general form of this engine somewhat resembles that for which Robert
Stirling obtained Letters Patent on or about the 1st of February 1827,
No. 5456, and the 1st of October 1840, No. 8652, respectively.
A is the working cylinder, and a the single-acting working piston; B is the
changing and supply cylinder, and 1, 2, the piston working therein, which, for
the sake of simplicity of description, I will for the present assume to be a
single-light piston; C is the main shaft supported by the frames r, r, and
having two cranks C' and C2 set at nearly right angles with each other; C³
is the fly-wheel; D, the valve chest, communicating freely with the chamber
E, and provided with three ports d, d', d'; within this chest works the valve
M; E is a small chamber, containing a regenerator F resting upon a central
cone f. At the lower end of the chamber E there are two nozzles or openings
e and e', one of which opens into the cylinder A, and the other into the cylinder
B, as represented, and they form a communication between the chamber E
and the cylinders. The lower portions of the cylinders A and B and chamber
E form the heating surfaces; X is the bed plate, which is supported by the
brickwork J; the cylinders A and B are supported near their centres by a
flange resting on the bed plate X, their lower ends projecting into the flue
below to receive the heat of the furnace. The cylinder A is open at its upper
end, whilst B is closed by a tight head. The pistons a and 1, 2, are made
somewhat longer than their stroke, and are filled with some non-conducting
material, in order to keep their upper sides as cool as possible. The piston a
is connected by the rod a' with crank C, whilst the piston 1, 2, has a rod b¹
passing through a stuffing box, and is connected by the short connecting rod 6³
with the crank C. The valve M is turned, so as to fit accurately the interior
of the valve chest D, and has a hollow throat of sufficient width to span any
wo adjacent ports d, d', and d. This valve receives an oscillating or par-

page_text: tially rotating motion in the following manner :-The axis of the valve passes
through the head of the valve chest D, and has a slotted lever m on one end,
as shewn at Figures 4 and 5. In the slot plays the roller i carried on the lever
I, which is in turn moved by the eccentric rod g. The regenerator F consists
Its
of a hollow cylinder composed of several thicknesses of wire cloth.
internal diameter is of the same area as the ports in the valve chest, and its
external diameter is greater according as the thickness of the regenerator is
increased. As the course of the cold air is from the centre of the regenerator
outwards, and as the air commences to receive heat and expand immediately
upon entering the regenerator, and constantly receives more heat until it
escapes at the periphery much increased in volume, it is evident that the area
of the passage way should increase from the cold to the hot side. This is
effected by the peculiar construction of the regenerator, the outside of the wire
cylinder (see Figure 3) having about double the circumference of the inside,
and giving an area of passage way proportioned to the bulk of the air at all
points, whether its motion be from the cold to the hot side or in the reverse
direction. Within the regenerator is the cone f, filling it at the bottom and
coming to an apex on a line with its top, thereby giving a large area for the
cold air to pass in at the top, whilst, as it flows off laterally through the regene
rator, a less area is required below. The taper of the cone f gives the proper
area at all points, and allows no more space for air than is absolutely required.
For the same reason the chamber E tapers outwardly from the top to the
bottom of the regenerator. The same effect is produced with a regenerator
made of thin plates of metal by making the spaces either wider or thicker at
the hot than at the cold end. A very convenient and desirable manner of con-
structing a regenerator of plates, in lieu of wire cloth, is to prepare a series of
thin plates much broader at one side than at the other, but of uniform thick-
ness throughout, and rivetting or bolting them together with washers of an
uniform thickness interposed between each plate and the next. The regenerator
thus formed may then be tightly fitted into a case E of corresponding wedge-
like form, the narrow end being uppermost or towards the cold end of the
cylinder. The cylinder H rests upon the bottom of the chamber E, so as to
be heated as nearly as possible to the same temperature as the metal upon
which it lies. From this cylinder a small tube h passes upwards through the
cone f, and thence through the side of the valve chest D, and is connected
with the chamber below the elastic diaphragm L; upon this diaphragm rests a
small plate having a rod connected with the weighted lever B. A link connects
this lever to another lever on the end of the spindle of damper 2 in the flue O.
The cylinder or vessel II is filled with some fluid that vaporises at a high

page_text: temperature, such as mercury, which will commence evaporating at about
650° Fahr. When this temperature is attained, a portion of the fluid will be
forced through the tube h, raising the diaphragm L and lever 1, by which
means the damper n is closed, the combustion in the furnace checked, and the
temperature of the heating surfaces reduced. As the temperature falls a
portion of the vapour of mercury is condensed and the diaphragm L sinks,
until the damper n is again opened and the fire quickened. Thus the tem-
perature of the heating surfaces is uniformly maintained at about the point
which the metal can safely bear. It is evident that the temperature of the
heating surfaces can also be regulated by connecting the lever with a slide
that shall admit cold air above the fire, which will cool the heaters both by
direct contact with them, and also by filling the chimney with cold air, which
will retard or check the draft. This portion of the engine is of very great
practical importance, as the change effected in the structure of the metal, in
consequence of being too intensely heated, has caused the failure of some
otherwise successful hot-air engines. It must be observed that the vessel H is
not in contact with the products of combustion, and that the motion of the
diaphragm L, lever 1, and damper n does not necessarily, and should not in
many instances, correspond with the fluctuations in the heat of the fire. The
vessel His within the chamber E, and is in contact with the inner side of the
heating surfaces at its base. Now, the heat of the products of combustion is
only one of the elements which tend to control the temperature of the vessel
H, the other being the power with which the engine is working. If the engine
be working very moderately and with little or no load, the temperature of the
vessel H may rise very nearly to the same point as that of the products of
combustion; but when it is working under the opposite conditions, the larger
quantity of air which is warmed in any given period tends to cool the interior
of the heating surfaces, and in order to maintain a uniform heat in the metal
it is necessary that the temperature on the exterior be considerably higher
than before. The apparatus is therefore intended to maintain a uniform tem-
perature, not in the gases, either on the exterior or interior, but in the metal
of the heating surfaces; and to produce this result, by so regulating the
draft through the fire as to supply just sufficient heat under all conditions.
This feature of the Invention is essentially important when the engine is fre-
quently stopped, as without it the metal is liable to become heated to a bright
red heat in a short time, and to become too much or too suddenly cooled when
it is again put in motion. The furnace K is supplied with fuel through a
suitable fire-door, and the products of combustion pass from the furnace, and
circulate around the bottoms and sides of the cylinders, and finally escape to

page_text: the chimney through the flue O. By allowing the products of combustion to
circulate in contact with the end of the working cylinder, as well as with that
of the changing cylinder, I am enabled greatly to increase the area of the
heating surface without at the same time increasing waste space. If the air
were passed through a pipe of sufficient length to give the same amount of
heating surface as the cylinder bottom, the pipe must have sufficient area
throughout its length to allow a free passage of the air, which involves an
amount of waste space that would seriously reduce the power of the engine;
but in this Invention the lower end of the piston is so formed as to fit the
cylinder bottom, and as at the end of its stroke it comes within a short distance
of it, the waste space is comparitively small.
Although the operation of an ordinary Stirling engine, on which my improve-
ments are based, is tolerably familiar to many, I may here explain that the
expansive power of heated air is rendered available therein by so operating a
working and changing piston in separate cylinders, that the changing piston
rapidly transfers a measure of air from its cold to its hot side, and then stands
nearly stationary while the working piston is forced up by the expansion of the
heated air, thereby imparting motion to the engine. The changing piston
then proceeds to transfer the same air back from the hot to the cold side of
the piston, in which transfer it is passed through a regenerator and refrigerator,
and its heat is there abstracted. By these means the pressure of the air is
very greatly reduced, and the working piston is therefore allowed to descend
with comparatively little resistance.
In this engine, as in Stirling's, a measure of air is transferred from the cold to
the hot side of the changing piston, and by its expansion the working piston
is forced up, and power is imparted to the engine. But at or about the
termination of the up stroke of the working piston, the difference becomes
apparent, for at this juncture the valve M by its rotation opens the eduction
port d, and allows the air to escape, while it also opens the induction
port d. As the changing piston descends, the space above it is filled by a
supply of fresh (or relatively fresh) air drawn either from the atmosphere or
from a reservoir. When this engine is worked with the air at only about the
atmospheric pressure, the fresh air is drawn directly from the atmosphere, as
represented in the Drawing, and the hot air beneath the two two pistons is
discharged and blown away. But it can, if desired, be worked in the same
manner under a high pressure by connecting a reservoir (not represented in
the Drawings) with the eduction and inductions ports d and d'. In such case
air is compressed by a pump until it fills the reservoir to any pressure desired,.
and the pressure within the engine will correspond therewith, and thus produce

page_text: a greater effect at each stroke; but when worked in this manner the engine must
be provided with a refrigerator analogous in structure (through not in arrange-
ment and effect equivalent) to Stirling's.
This engine differs from Stirling's in the following points; videlicet, Stirling's
alternately transfers the same air from the cold to the hot side of the changing
piston, and vice versa; whilst this discharges the hot air and draws in a supply
of other air at each stroke, Stirling's involves a loss of space in the refrigerator,
which is analogous in effect to that caused by what is known a "clearance
in steam engineering, which loss I avoid, because when the ports d and d
communicate with the atmosphere no refrigerator is employed, and when they
communicate with a reservoir of compressed air, the refrigerator is outside of
or beyond the valve, and its pipes and fittings form a portion of the reservoir,
and not a portion of the space within the cylinders. The space involved in the
refrigerator is not therefore equivalent to clearance in this engine, and is of no
effect whatever in the same.
The peculiar motions of the two pistons in relation to each other could be
effected by means of cams, but cranks afford a smoother motion, and allow a
more rapid action from the tightness at which the parts can be maintained, and
the very gradual manner in which the changes occur. For this reason the
two cranks C and C² are placed at nearly right angles with each other. I.
find that the engine performs best when the crank C is about 75° forward of
the crank C. The relative motions imparted to the pistons by the cranks is
best shewn by the diagram Fig. 15, in which the circle of the cranks is divided
into four parts. Let the crank C' be at 1, and the crank C² at 2; now if the shaft
C, be turned to the right one-fourth of a revolution, C¹ will be at 2, and C at 3,
and the piston attached to the crank C' will have passed through about five-
sevenths of its stroke, whilst the piston attached to the crank C will have moved
up and down through one-seventh of its stroke. During another fourth of a revo-
lution, C¹ will move up and down through one-seventh of its stroke, whilst C³
will pass through its five-sevenths. Thus it will be seen that the cranks give
very nearly the desired motions.
The motion of the changing piston can be made still more rapid with a longer
pause at its highest position by shortening the connecting rod 6, if such a motion
is considered desirable, but this principle carried too far would destroy the smooth-
ness of the motions due to the crank, and would thus become an objection.
Figs. 4 and 5 shew the valve gearing. The valve is mounted on a spindle
M', keyed to which is a slotted lever m, and I is another lever driven by an
eccentric rod g, and turning on a fixed stud T, a roller i being mounted on this
lever as before stated; the stud T being above M'; and the lever I vibrating to

page_text: nearly equal distances on each side of a horizontal line passing through the
centre of the stud T; it follows that the roller i will play longer in the slot
during the upward than during the downward stroke, as shewn by the dotted
lines; it will also be seen that only a slight motion is imparted to the valve,
except in the middle of the stroke of the eccentric, when the valve will be
rapidly moved from one position to the other, also that the valve requires to be
turned in the upward position about two-thirds of the time, and in the down-
ward about one-third, and to be rapidly transferred from one position to the
other. These peculiar motions are effected by the combination of the eccentric
with the link and slotted lever, as here represented.
seen.
Having now explained the several parts, I will proceed to describe the
operation of the machine. By referring to Figs. 6, 7, 8, 9, 10, 11, 12, and
13, the positions of the pistons and valve at each eighth of the stroke can be
The circle above each diagram shews the position of the cranks, the
crank C¹ carrying the working piston a, and the crank C carrying the
changing piston. The pressure of the air in the cylinders is denoted in each
diagram by the red figures; these figures may not be strictly correct, but they
will suffice to illustrate the mode of operation. Suppose the valve in starting
to be in the position shewn by Fig. 6, the piston a has nearly completed its
up stroke, and the piston 1, 2, has just commenced its down stroke, whilst the
induction and eduction ports have commenced to open. If now the main
shaft be turned to the right one-eighth of a revolution, the various parts will
have assumed the positions shown in Fig. 7. In this Figure the piston a has
completed its up stroke, and the piston 1, 2, has performed one-half of its
down stroke, drawing in a supply of cold air to fill the space above it, and
forcing the hot air beneath it out through the regenerator, where it loses a
portion of its heat, and then escapes through the exhaust port. At the next
eighth of a revolution (see Fig. 8) the piston a has commenced its down
stroke, and the piston 1, 2, has nearly completed its down stroke.
this point the valve M closes both the induction port d¹ and eduction port d,
and opens a communication through the cylinder port d between the upper
side of the piston 1, 2, and the lower side of the pistons a and 1, 2. At the
next position (see Fig. 9) the piston a has moved down a half stroke, and the
piston 1, 2, is at the bottom of its stroke. In Figure 10 the piston a has
nearly completed its down stroke, having forced the hot air beneath it up
through the regenerator, and out through the port d, during the early part of
its downward motion, and compressed it with the air above 1, 2, during the
latter portion. This compression of course requires considerable power, and
necessitates a heavy or quick running fly wheel, but it greatly increases the
At or near

page_text: pressure during the up stroke, and serves to overcome the momentum of the
parts, having in this respect the same effect as cushioning by the early closing
of the exhaust in steam engines. In this Figure the piston 1, 2, has just
commenced its up stroke; in Fig. 11, the piston a has completed its down
stroke, and the piston 1, 2, has performed half its up stroke. In Fig. 12, the
piston a has commenced, and the piston 1, 2, has nearly completed, its up
stroke, and the latter has driven the cold air which was above it down through
the regenerator, absorbing the heat previously treasured in its metal. The
air then flows in contact with the bot surface below, and fills the space
beneath both the pistons 1, 2, and a at a greatly increased pressure and tem-
perature indicated by the red figures. In Fig. 13 the piston a has been forced
by the pressure below it through half of its up stroke, the piston 1, 2, being
at the end of its up stroke. At the next eighth of a revolution the parts
have again assumed the position shown in Fig. 6, the piston a having nearly
completed its up stroke, and the piston 1, 2, just commenced its down stroke,
the exhaust and induction ports being just opened.
In this engine the pressure acts only in one direction to force the piston up
the momentum of the fly wheel, serving to complete the downward stroke
against a gradually increasing back pressure; but by obvious means two air
engines of the character herein represented may be combined so as to form
a double-acting engine.
In operating the engine as above described a considerable loss of effect is
experienced from the fact that heat is conveyed through the material of the
changing piston, and imparted to the air immediately on its entering the
space above it. The heat thus imparted to the air first received causes it to
expand, and obstruct the ingress of that which should follow. The result of
this is that less air is received than would be required in a cold state to fill
the space formed by the sinking of the changing piston, and less power is
therefore developed by the engine. It is also found that much heat is con-
veyed upward through the working piston, and that the top of the same
becomes so highly heated that the lubricating material is injuriously affected
unless much care be taken to prevent it. This evil can only be partially
remedied by increasing the thickness of the piston, and any such increase of
the material involves serious difficulties by increasing the size of the engine
and the inertia of the parts.
I therefore construct the changing piston in two parts, 1 and 2, as repre-
sented in Fig. 1. The lower part 1 is made hollow, and is filled with ashes
or other good non-conducting material, and is of slightly less diameter than

page_text: the cylinder as represented, so that a narrow annular space exists between its
periphery and the interior of the cylinder B.
The parts 1 and 2 are secured rigidly together by webs or other equivalent
connections, but the connecting parts are not of sufficient area to be of much
effect in conveying heat from 1 and 2. In the space between the two parts
of the piston 1 and 2, I provide a suitable seat, and an annular or other self-
acting valve S, which allows the air to flow at pleasure from, the upper or
cold side of the piston to the lower or hot side, but prevents its return.
The operation of the engine as thus improved is as follows:-Upon the
descent of the changing piston 1, 2, the air is drawn in through the valve D
as before described, but when it rises, instead of all the air passing through
the valve chest D and the regenerator F, a portion passes through the valve S
between the parts 1 and 2 of the piston, and thence around the outside of
the part 1, where it is heated and expanded, and serves to impel the engine
by forcing up the piston a. When its useful effect is ended, it is discharged
through the valve M, the valve S closing to prevent its returning again to the
top of the cylinder B. By this conveyance of a portion of the inducted air
between the lower part 1 and the upper part 2 of the changing piston, the
heat which is conducted or radiated upwards into the top part 2 is removed
by the stream of air which is passing, and the inducted air instead of playing
directly upon the hot top of the part 1, and becoming prematurely expanded
with the ill effect of thereby preventing the ingress of the full and proper
quantum of air, plays upon a cool surface on the top of the part 2, and is not
allowed to come in contact with the lower part 1 until the piston begins to
ascend. The proportion of the air which is necessary to pass through the piston
in this way for this purpose is determined by the amount to which the valve S
is allowed to open. The form of the working piston a which I have adopted
in my improvement is shewn by the section in Figure 1. A clear space Qis
allowed to extend quite across the piston with the exception of a thin shell at
the periphery, and the lower extremity of the connecting rod a¹ is joined to
the piston a, not through the aid of a continuous plate as heretofore, but of an
open frame which extends from the centre to the circumference, forming a
strong connection between the rod a¹ and the lower portion of the piston a,.
but with the liberal openings through which the air may circulate. As the
working piston a reciprocates rapidly, the agitation of the air contained in
the space Q, and of the air immediately above, is sufficient to induce a partial
displacement of the air at each stroke, so that the space Q is always filled
with air at a comparatively low temperature, which by its circulation conveys

page_text: away the heat conducted upward to the rubbing surfaces. If no air space Q
existed in the piston, or were it enclosed by the employment of a tight plate
above, so that the contents of Q would not be displaced in part at each stroke,
the rubbing surfaces at the top of the piston would be compelled to sustain a
much bigher temperature, the heat at the bottom of the piston diffusing itself
more uniformly throughout its whole substance.
I will now describe that modification of my Invention in which the heat is
obtained by burning any combustible gas, such as bicarburetted hydrogen, for
example. Within the cylinders I inject a proper quantity at each stroke by a pump
or equivalent means, and ignite it. The heat applied in this manner is, for obvious
reasons, more efficient than when applied to the exterior of the cylinders.
Many efforts have been heretofore made to apply the heat of combustion
directly to the air in the cylinders, or otherwise to use the gaseous products of
combustion in a cylinder, as a means of obtaining power; but when coal or
other solid fuel is employed, small particles of ashes and of unburnt fuel are
liable to adhere to the rubbing surfaces of the piston and cylinder, and cause
them to wear rapidly. Combustible gas may, however, be burned in such
situations without involving this evil.
The combustion of hydrogen or of bicarburetted hydrogen in the proper
amount of atmospheric air produces a very intense heat, and a corresponding
pressure. Many attempts have been made to utilize this power by mixing
the gases in given quantities within a cylinder, and then exploding the mixture.
These forms of engines, though they have been successful in developing con-
siderable power, have failed to become of practical utility from the fact that
the concussions. resulting from the sudden explosions have been too violent..
Other difficulties have also presented themselves in practice, such as the over-
heating of the cylinder and piston, the uncertainty of igniting the mixture,
and the difficulty of economizing the heat when generated. All these evils
are overcome by my improved engine, which may be made in various forms,
one form being represented in Fig. 14, the construction of which I will now
proceed to describe. A is the working cylinder; a, the working piston;
B, the changing cylinder; 1,2, the changing piston, which in thus Drawing
is made solid; D, the valve box, and E the chamber of the regenerator, these
parts being essentially the same as those heretofore explained. Y is a gas
burner or series of gas burners, and y is a gas pipe, through which the gas is
supplied from the pump V. This pump is worked by the engine in any con-
venient manner, so as to supply the gas during the first half of the ascent of
the changing piston 1, 2. W is an igniter of any suitable character upon
which the gas jets from the burner Y impinge. The igniter W may consist

page_text: of a plate or coil of metal heated by a current of electricity; or it may be a
hollow shell of metal heated by a separate jet of gas, or by a blow-pipe flame
extending into it from the outside of the cylinder. The jets of gas issuing
from the burner or burners Y are supplied with oxygen from the fresh air
which flows down through the regenerator, and the heat produced by the
combustion elevates the temperature of the contents of the cylinders.
The difficulties previously enumerated as applying to former attempts to
produce power by the combustion of gas within the engine are overcome by
the following means: To avoid the destructive effects that must follow from
repeated explosions in the working cylinder of an engine, I do not furnish a
mixture of air and gas to be exploded, but by means of the gas pump Va
measure of gas is gradually supplied to the air that is passing Y on its way
from the upper to the under sides of 1, 2. The gas immediately comes in
contact with an igniter W, and burns with a blaze like an ordinary gas jet,
the temperature and pressure gradually increasing as the pump V completes
its stroke. In order to obtain the greatest effect of the heat, and guard against
too high a temperature, the pump V is made to complete its stroke before the
piston 1, 2, has finished its up stroke, so that the first air may be heated and
expanded to the utmost extent, and the working piston a receive the greatest
impulse; but if such an excessive heat were continued throughout the stroke,
the regenerator, cylinders, and pistons would soon be destroyed. This evil is
prevented by so operating the pump V that it shall complete its stroke at
about the middle of the up stroke of the piston 1, 2, so that at this point the
supply of gas ceases, and the last half of the air coming into the lower part
of B mixes with the first half, and reduces its temperature, making the average
temperature such as the metal can safely endure. To prevent leakage and
loss of heat, the parts of the engine subjected to a high temperature are
surrounded by a wrought-iron jacket, about an inch larger on all sides than
the cast-iron cylinders, and the space between the two is filled with plaster or
any good non-conductor; this prevents the radiation of heat, and consequently
economises gas. The tight jacket also prevents any leakage, though the
cylinders may be porous or cracked.
The thin sleeve surrounding the piston rod b', in Fig. 1, shews a method
which I have devised for mounting the valve S (in lieu of or additional to),
the spring S'. I render available the friction of the packing in the stuffing-
box for operating the valve S¹. As the piston 1, 2, ascends, this friction
tends to open S¹, and the moment the piston 1, 2, begins to descend, the
friction (either alone or acting in conjunction with the spring S¹) closes the
valve, and holds it tightly closed during the entire descent.

page_text: The advantages obtained by this Invention are,-
Firstly, I dispense with pumps and coolers, and at the same time run at
high speeds without noise.
Secondly, by employing the ends of both the working and the changing
cylinders as heating surfaces, I reduce the lost space in proportion to the
amount of heating surface, and thereby proportionally increase the power of
the engine.
Thirdly, the heat regulator or limitor protects the heating surfaces from the
destructive effects of an extremely high temperature, and regulates the fire,
thereby keeping the interior of the heating surfaces at a nearly uniform degree
of heat under all conditions.
Fourthly, the area of passage way through the regenerator is proportioned
to the bulk of the air at all points, and the resistance to the passage of the air
is thereby much reduced.
Fiftbly, the valve M, moved as described, performns the threefold office of
induction, eduction, and equilibrium valve with less friction and less liability
to derangement than any means previously known, and (what is very
important) the necessity for as much air space within the passage as in
previous valves.
Sixthly, the upper part of the changing piston and cylinder are kept at a
comparatively low temperature by the circulation of a portion of the cool air
through the double piston 1, 2, allowing the full amount of cool air to be taken
in at each stroke, whilst at the same time I obtain nearly or quite the full
effect of the regenerator.
Seventhly, the free circulation of air into the open space Q in the upper
part of the working piston serves to keep the rubbing surfaces cool, and prevent
the burning of the lubricating material.
Eighthly, by the use of gas burned within the cylinders in the manner
described an intense heat is obtained, and the engine rendered useful and
convenient in circumstances where the usual forms could not be introduced.
Ninthly, by producing combustion within the engine in a portion of the air
which is passing through it, and mingling the other air which has not been
affected directly by the combustion with the air which has received its full
effects, a safe temperature is obtained.
Having now described and particularly ascertained the nature of the said
Invention, and the manner in which the same is or may be used or carried
into effect, I would observe, in conclusion, that what I consider to be novel
and original, and therefore claim as the Invention secured to me by the
herein-before in part recited Letters Patent, is,-

page_text: 1st, the general construction and arrangement of hot-air engines, as herein-
before described.
2nd, the peculiar combination and arrangement of the changing cylinder B
and the working cylinder A, with the valve or valves by which the piston 1, 2, is
made, both to change the air from the cold to the hot end of the cylinder, and
to receive a fresh volume for the next stroke, as herein-before described.
3rd, the system or mode of allowing the products of combustion to circulate
in contact with a portion of the exterior of both the working and the changing
cylinders, for the purposes herein-before described.
4th, the system or mode of automatically regulating the temperature
of the interior of the heating surfaces in the chimney O, as herein-before
described.
5th, the peculiar construction of the regenerator, whereby an increasing
area of passage from the cold to the hot side is obtained, as herein-before
described.
6th, the system or mode of working the single valve M in combination with
the two pistons a and 1, 2, so as to accomplish the threefold purpose of
induction, eduction, and equilibrium valve, as herein-before described.
7th, the system or mode of dividing the changing piston 1, 2, into two or
more parts, and conducting a portion of the air through the space between
such parts in its transfer from the cold to the hot end of the cylinder, in the
manner and for the purposes herein-before described.
8th, the system or mode of cooling the packing in the working piston
by the free circulation of the external air in the space Q, as herein-before
described.
9th, the system or mode of gradually heating the air in a hot-air engine,
by burning jets of combustible gas in the interior of the cylinders, or within
chambers communicating therewith, as herein-before described.
10th, the system or mode of reducing the temperature of the engine when
combustion takes place within it, by mingling other air at a lower temperature
with the products of combustion, as herein-before described.
.
In witness whereof, I, the said John Henry Johnson, have hereunto
set my hand and seal, this Thirtieth day of July, One thousand eight
hundred and sixty..
J. HENRY JOHNSON.
(1)
J. HENRY JOHNSON
(ra)