IMPROVEMENTS IN HOT AIR ENGINES
Year: 1880

page_text: PROVISIONAL SPECIFICATION left by George Herbert Lloyd and John
Edward Rogers at the Office of the Commissioners of Patents on the 22nd
January 1880.
GEORGE HERBERT LLOYD, of the Firm of Thomas Piggott and Company, of
Birmingham, in the County of Warwick, Gas Engineers, and JOHN EDWARD
ROGERS, of Smethwick, in the County of Stafford, Machinist. "IMPROVEMENTS IN
HOT AIR ENGINES."
Our Invention has reference to motive power engines actuated by heated atmos-
pheric air or other aëriform fluid, and commonly called hot air engines; and our
said Invention consists of the construction and arrangement of parts of the said
engines herein after described, whereby a simple, efficient, and economical hot air
engine is produced.
We will describe a hot air engine of the simplest form made according to.our
Invention. The said engine consists essentially of five parts, namely, a pressure
accumulator or reservoir containing air, by preference of a pressure of eighty
pounds on the square inch; two cylinders and pistons similar to those of a steam
engine, and a condenser containing air under a pressure, by preference, of forty
pounds on the square inch, and of a heating chamber through which the air passing
from the reservoir is heated before entering the first or hot air cylinder. The air
employed circulates through the apparatus, passing from the reservoir to the heating
chamber, from thence to the first or hot air cylinder; after having acted upon the
piston in that cylinder it passes to the condenser, where it is cooled, and from
thence to the second or cold air cylinder. Finally, it returns to the reservoir from
the cold air cylinder. The reservoir and condenser are immersed in water to
keep them and the air contained in them cool, and the two cylinders are jacketed,
the first or hot air cylinder having a case containing air, by which its cooling is
prevented; the second cylinder having a casing containing water, by which it is
kept cool. The cylinders are provided with slide valves resembling those of a
steam engine, and the piston rods of the two cylinders are connected with cranks
on the same shaft, to which shaft rotary motion is communicated by the cylinders.
The passage between the reservoir and heating chamber is provided with a stop
valve and a back pressure valve, the former to regulate the flow of air from the
reservoir, the latter to prevent the return of air from the heater to the reservoir.

page_text: The passage between the cold air cylinder and reservoir is provided with a back
pressure valve.
The action of the engine is as follows:-
Air, say, of eighty pounds pressure, passes from the reservoir to the heater; by
the heat it there acquires it is expanded, say, into double the volume, having the
original pressure, or about the original pressure. The heated air acting on the
piston of the hot air cylinder urges it from end to end of the cylinder. By the
action of the slide valve the communications are reversed, the air which has filled
the cylinder being put in communication with the condenser, and hot air from
the heater is at the same time admitted to that end of the cylinder which was
previously in communication with the condenser. The air which enters the con-
denser is rapidly cooled, and its pressure reduced to, say, forty pounds on the
square inch. The cold air cylinder in communication with the condenser has its
slide valve set backwards, so that it acts as a pump for compressing the cold air of
the condenser, and returning it in its compressed state to the reservoir. Cold air
of, say, forty pounds pressure, passes from the condenser to the cold air cylinder as
the piston passes from one end of the cylinder to the other end. On the piston
making its return stroke this air is compressed by the motion of the piston, until
the piston having made half its stroke the pressure of the air is doubled, and it
now has the pressure of eighty pounds on the square inch, in which state it returns
to the reservoir to pass again to the heater and hot air cylinder. It will thus be
understood that the effective power of the engine at each stroke of the hot air
piston is the power due to the pressure of eighty pounds on the square inch on the
said hot air piston, diminished by the equal resistance of the cold air piston
through the second half of its stroke, and the resistance gradually changing from
forty to eighty pounds pressure during the first half of its stroke. The motion of
the crank shaft is equalized by a fly wheel.
The engine we have described is the simplest form of our Invention. Several
of the hot and cold air cylinders may be combined, and where, as in locomotive
and marine engines, a uniform and easily reversible motion is required, we so
arrange the cranks with which the cylinders are respectively combined that the
shaft rotates with a uniform or nearly uniform power, and has no dead points.
We prefer to make the faces of the slide valves and their seats curved instead
of plain, and the valve mechanism may be worked so that the hot air may be cut
off at any part of the stroke of the piston and the hot air used expansively.
In order to facilitate the starting of the engine, as well as to assist engines
requiring to be readily reversed, we use a relief chamber, in which the cold air
behind the piston of the cold air cylinder is for a time received, thereby allowing
the cold air of the condenser to act more efficiently on the other side of the piston.
After the engine has been started or reversed communication with the relief
chamber is cut off, the air in the relief chamber being returned to the reservoir by
an auxiliary pump, which pump also supplies any deficiency of air occasioned by
leakage.