IMPROVEMENTS IN HOT AIR ENGINES
Year: 1881

page_text: PROVISIONAL SPECIFICATION left by Alexander Melville Clark at the Office
of the Commissioners of Patents on the 4th February 1881. A communication
from abroad by Azel Storrs Lyman, of the City, County, and State of New
York, United States of America.
ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the County of Middlesex,
Patent Agent. "IMPROVEMENTS IN HOT AIR ENGINES." [A communication from
abroad by Azel Storrs Lyman, of the City, County and State of New York, United
States of America.]
This Invention relates to that class of hot air engines which are charged with a
high pressure and use the same air or gas continuously by merely moving it back
and forth between the working cylinder and the cooler and heater of the generator.
The object is to avoid the practical defects which have prevented the successful
introduction of this class of engines, and the Invention consists in certain novel
features of construction whereby this object is attained.
The generator consists of three main parts, viz., the upper part or cooler, which
is surrounded by an outer jacket forming a water space; the lower part or beater,
which is made of heavy cast iron or steel, which will endure high heat, and which
is connected with the heater of the working cylinder, and the centre part, which is
made of light and strong lap welded sheet iron or steel tubing, which will not
conduct heat readily, and which has a bore larger than the outside of a displacer
contained within the generator for the reception of the economizer or regenerator
between the two. The displacer is moved up and down by a rod and cam in the
operation of heating and cooling the air. The lower portion of the displacer is
made of cast metal, and the central portions of thin sheet metal, which will not
readily conduct heat, and it is solidly packed full of dry fire clay or other bad
conducting material. The tube of the generator surrounding the displacer is for
the purpose of forming an economizer or regenerator, formed by wrapping a sheet
of thin metal or a series of narrow sheets one above the other. These sheets are
kept apart a distance about equal to their thickness by indentations forming small
projections, which are made a short distance apart, about four to a square inch, so
as to preserve each sheet in its circular form and retain them at equal distances
apart.

page_text: The working cylinder consists also of three main parts, viz., the lower casting or
heater, the central part of lap welded sheet iron or steel, and the upper part, which
is surrounded by a water jacket. The working piston or plunger is also in three
parts, an upper solid portion, the lower part or heater, preferably of cast steel, and
the central part of sheet metal firmly packed with nonconducting material. The
compressed air reservoir is fixed directly below the working cylinder, and the
balance pressure plunger, which works up through the bottom of this reservoir, is
of the same area as the working plunger, and supported by the crosshead below it,
the same crosshead combining the double pump rods with the single pump rod,
which is directly below the working cylinder. A small pump for compressing air
is driven by the same engine which charges the compressed air reservoir, and this
reservoir is connected with the engine by a small tube that has in it a check valve
which allows the air to pass freely into the engine and prevents it from
flowing back down into the reservoir. A safety valve in this tube prevents
overcharging.
The operation is as follows:-Suppose the displacer of the generator and the
plunger of the working cylinder both down to the bottom, and the air in it nearly
all above the displacer and cold, and that its pressure equals 10 atmospheres, if the
area of the piston is 10", the pressure of air up against it is 1500 lbs. This is
balanced by the pressure of 1500 lbs. on the balance pressure plunger. Now I
raise the displacer to the top, and the cold air above it is all forced down below
and heated, say, 500°, when its pressure, is doubled, that is, it presses 300 lbs. per
inch in every part of both cylinders. This pressure of 300 lbs. per inch under
the 10 inches area of the piston of the working cylinder lifts 3000 lbs., and
besides raising the balance plunger applies 1500 lbs. to doing work. When it has
lifted the piston up 1 of its stroke the air has expanded so much that it lifts but
3/4 as much extra as at the start or 1125 lbs.
The extra upward pressure rapidly diminishes, while the downward pressure on
the balance pressure plunger increases more or less rapidly as the compressed air
reservoir is smaller or larger.
Next, while the crank of the working engine is passing its dead centre at the top
the displacer is moved to the bottom, and the air is above it and cooled and presses
but, as much as it did the moment before. A part of the hot air under the
working piston has also rushed off up into the cold air chamber above the displacer
until the pressure under the piston is no greater than it is in the cold air chamber.
But the air occupies nearly double the space that it did before starting, because of
the raising of the working piston, and of course the air presses but 75 to 100 lbs.
per inch, that is, 750 to 1000 lbs. under the working piston, and this will not
support the downward pressure of over 1500 lbs., and on the balance plunger this
weight brings the piston down with great force at the start and gradually decreasing
till it is very little near the close of its stroke.
When the crank is passing its dead centre at the bottom and the displacer is
again raised, the air heated, and the same movements are repeated by the same
causes.
Where a number of working pistons are lifting upon one cross head the area of
the balance plunger should of course equal that of all the working cylinders, proper
reduction being in all cases made for the weight of the pump rods, cross heads, and
other weight that may be supported by the working piston.
The area of the generator being four times as great as that of the working
cylinder, and its stroke one third as great, it heats and cools more air than is
required to run the engine with a charge of 480° in the temperature of the air
may be made to do very economical work by increasing the stroke of the displacer
to half that of the working plunger, thus heating twice as much air when it will
require to be expanded but half as much.
The object of arranging the engine in this form with the working cylinder fully
open at one end while the generating cylinder is closed is so that I can load the
working plunger, and thus be enabled to charge with a heavy pressure and make.

page_text: it double acting. Instead of the compressed air reservoir and balance plunger a
simple weight may be suspended in place of the balance pressure plunger or placed
above if desired. Where two engines are used for turning a shaft it will in some
cases be best to set their cranks 180° apart, and thus dispense with the compressed
air balance plunger or the weight. In other cases it will be convenient to connect
the engines with the opposite ends of a rock shaft. This charging with compressed
air also enables me to very greatly increase or lessen the power of the engine at a
moment's notice by having a reservoir of air at a much higher pressure, from which
the additional pressure may be drawn if needed. By this arrangement it will also
be seen that I use hot air in my working cylinder while all the friction surfaces are
cold.