IM- PROVEMENTS IN HEATED AIR ENGINES
Year: 1867

page_text: LETTERS PATENT to Francis Herbert Wenham, of 1, Union Road,
Clapham, in the County of Surrey, Engineer, for, the Invention of "IM-
PROVEMENTS IN HEATED AIR ENGINES."
'
Sealed the 31st December 1867, and dated the 15th August 1867.
PROVISIONAL SPECIFICATION left by the said Francis Herbert Wenhain
at the Office of the Commissioners of Patents, with his Petition, on
the 15th August 1867: **
I, FRANCIS HERBERT WENHAM, of 1, Union Road, Clapham, in the County
of Surrey, Engineer, do hereby declare the nature of the said Invention
for "IMPROVEMENTS IN HEATED AIR ENGINES," to be as follows:-
This Invention consists in so arranging the top of the cylinder that it shall
act as an air pump.
In hot air engines the body of air forced into and heated by the furnace
must be less in bulk than the capacity of the cylinder, as determined by one
stroke.of the engine. In order to obtain this condition the top of the piston
has been made with a trunk or hollow rod of 'large' diameter, passing air-tight
through a gland in the lid of the cylinder,. the upper portion of which is
thus made annular and reduced in capacity, and serves as the air pump.
My Invention is for causing the upper portion of the cylinder to discharge
the requisite quantity of air without a trunk which has been found objectionable
in practise. provide the top of the cylinder with a sliding or other valve,
opening to the external air; this serves as the inlet valve of the pump.
After

page_text: the piston has descended to the bottom of the stroke this valve remains open
for a portion of the return stroke, so that some of the air that has just entered
is allowed to escape again into the atmosphere. At the time when the air
pump contains the requisite charge of air (varying in quantity from three-
fourths to one-half the lower capacity of the cylinder) the inlet valve is
suddenly closed by the action of the engine, and the volume of air is forced
through the usual outlet valve into the furnace; or the inlet valve may be
propped open, and the support removed when the proper charge of air is
contained. As this would preferably be a variable quantity according to the
required work on the engine the closing of the inlet valve may be determined
at varying parts of the stroke by the action of the governor, which will in this
way regulate the speed of the engine.
By another arrangement I make the upper end of the cylinder of such
capacity that when the piston reaches the top of the stroke a space may be
left in which the portion of air not required may be compressed, and conse-
quently will not enter the furnace, and by.its subsequent expansion will assist
the down stroke of the piston; this space may be formed between the piston
and cylinder lid, or the air may be compressed in a side passage or reservoir.
In these engines I prefer carrying the crank shaft in bearings bolted to the
top flange of the cylinder, and working the crank by a return connecting rod
with guides for the piston rods above, similar in form to that. known as a
steeple engine;" in other respects, as in the furnace and valve arrangements,
the parts are substantially the same as described in my Patent dated 18 March
1867. No. 776.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Francis Herbert Wenham in the Great Seal Patent Office
on the 10th January 1868.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, FRANCIS
HERBERT WENHAM, of 1, Union Road, Clapham, in the County of Surrey,
Engineer, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Fifteenth day of August, in the year of our Lord One
thousand eight hundred and sixty-seven, in the thirty-first year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me,
the said Francis Herbert Wenham, Her special licence that I, the said
Francis Herbert Wenham, my executors, administrators, and assigns, or such

page_text: others as I, the said Francis Herbert Wenham, my executors, administrators,
and assigns, should at any time agree with, and no others, from time to
time and at all times thereafter during the term therein expressed, should
and lawfully might make, use, exercise, and vend, within the United Kingdom
of Great Britain and Ireland, the Channel Islands, and Isle of Man, an
Invention for "IMPROVEMENTS IN HEATED AIR ENGINES," upon the condition
(amongst others) that I, the said Francis Herbert Wenham, my executors
or administrators, by an instrument in writing under my, or their, or one
of their hands and seals, 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 Francis Herbert Wenham, do hereby
declare the nature of my said Invention, and in what manner the same
is to be performed, to be particularly described and ascertained in and by
the following statement:-
This Invention consists in so arranging the top of the cylinder that it shall
act as an air pump.
In hot-air engines the body of air forced into and heated by the furnace
must be less in bulk than the capacity of the cylinder as, determined by one
stroke of the engine. In order to obtain this condition, according to one
method I provide the top of the cylinder with a sliding or other valve
opening to the external air; this serves as the inlet valve of the pump. After
the piston has descended to the bottom of the stroke this valve remains open
for a portion of the return stroke, so that some of the air that has just
entered is allowed to escape again into the atmosphere; at the time when the
air pump contains the requisite charge of air (varying in quantity from three-
fourths to one-half the lower capacity of the cylinder) the inlet valve is
suddenly closed by the action of the engine, and the contained volume of air
is forced through the usual outlet valve into the furnace; or the inlet valve
may be propped open, and the support removed when the proper charge of air
is contained; as this would preferably be a variable quantity according to the
required work of the engine the closing of the inlet valve may be determined
at varying parts of the stroke by the action of the governor, which will in
the way regulate the speed of the engine.
By another arrangement I make the upper end of the cylinder A, A, Figs. 1
and 2, of such capacity that when the piston 6 reaches the top of the stroke
at C a space D may be left in which the portion of air not required may

page_text: be compressed, and consequently' will not enter the furnace, and by its
subsequent expansion will assist the down stroke of the piston. This space
may be formed between the piston and cylinder lid, or the air may.be: com-
pressed in a side passage or reservoir:. In these engines I prefer carrying
the crank shaft e in bearings bolted to the top of the flange of the cylinder, and
working the crank by a return connecting rod with the guidés g for the
piston rods above, similar in form to that known as a "steeple engine;" in
other respects, as in the furnace and valve arrangements, the parts are sub-
stantially the same as described in my Patent, dated Eighteenth March, One
thousand eight hundred and sixty-seven, No. 776; but as an additional improve-
ment I place a disc of fire-clay above the furnace, as shewn at h, Fig. 1; this
is supported on the room of the fire-pan, and has a central hole equal in
diameter to the bore of the fuel hopper i which touches the disc, and the
bottom edge is thus protected from the direct heat of the fire. Around the
disc are; a series of perforations J, shown in plan Fig. 3, leading into the
annular space of the stove; a jet of pure flame rises through each of these at
every stroke of the engine, and at the same time the fire is prevented from
rising above its proper level.
Having thus described my Invention I would have it understood that I
claim the methods of employing the top of the cylinder as an air pump, with
the means of regulating or limiting the proper measure of air sent into the
furnace at each stroke as described.
In-witness whereof, I, the said Francis Herbert Wenham, have hereunto
set my hand and seal, this Tenth day of January, in the year of our
Lord One thousand eight hundred and sixty-eight.
FRANCIS HERBERT WENHAM. (L.S.)
1.