The Stirling Engine 1841 patent

Source: an article from The Mechanics' Magazine, Vol. XLV, Page 559 - Part 2
Date: July 4th - December 26th, 1846
Title: Abstract of specifications of English patents recently enrolled
Patent: # 8652
Editor: J. C. Robertson

This abstract relates the important part of the Stirling 1841 patent. Noteworthy is the difference between the here described contrivance and arrangement versus the practical engine made by his brother James.

James Stirling, of Dundee, Engineer, and Robert Stirling, of Galston, Ayrshire, D.D., for certain improvements in air-engines. Enrolment Office, April 1, 1841.

The engines referred to in this patent are those in which motion is obtained by the alternate expansion and contraction of air, by the application or abstraction of caloric.

An "air vessel" is formed of cast iron, and connected by a port and pipe with the top of a cylindrical cast iron vessel called the "plate box"; the air vessel also communicates at its lower part with the plate box by three or more parallel pipes, which terminate within the air vessel in fan shaped orifices for the purpose of rapidly spreading the air over the whole extent of spheroidal face of the air vessel.

An air-tight cast iron vessel called "the driver", occupies 5/6ths of the air vessel, and in order to prevent heat from ascending, this driver has a cast iron plate fixed outside its bottom, and in its lower part is placed a quantity of brickdust or other non-conducting material; the remainder of the interior is divided into 12 or 16 compartments by thin iron plates.

The driver is made to fit the bored part of the air vessel, so as to move easily up and down, but not to allow air to pass by its side; its upper and lower end are so formed as to fit the top and bottom of the air vessel. The driver is moved by a piston rod passing through a cupped leather collar, fixed on the top of the air vessel, in which also there is a pipe descending into a vessel of oil, so as to prevent access of air to the collar, and thus make the joint air-tight.

Another kind of driver consists of an outer shell of cast iron, accurately turned and fitted to the air vessel and having a number of holes pierced in its bottom for the passage of air; upon the bottom of this shell rests a piece of cast iron, similarly pierced, having small ridges on its upper surface to support a number of plates and facilitate the distribution of air among them; these plates consist of alternate sheets of plain and fluted glass, in narrow strips not exceeding an inch in width, which accurately fill up the interior space of the driver. At a small distance above these plates is the cover, which is perforated with small holes for the transmission of air, and is attached to the outer shell by a ring of sheet iron.

The "plate box", about 2/3 from the bottom, is filled with perpendicular plates of iron kept at 1/50 of an inch (approx. 0.5 mm) from each other by ridges; the remainder of the plate box is occupied partly by blocks of iron, glass, or other solid bodies, and partly by a refrigerating apparatus, composed of a great number of copper pipes, through which a stream of cold water circulates, arranged in 27 horizontal rows, at a distance of 1/20 of an inch (approx. 1.3 mm) apart. These pipes are soldered into two brass plates, and to these two other plates of brass are soldered, having horizontal passages at their four margins for connecting the ends of the pipes and returning the water from one end to the other, furnished with larger passages for introducing and carrying off the water. The main pipes pass through holes in the cover of the plate box, made tight with lead packing.

The modus operandi is as follows:
The bottom of the air vessel, the parallel pipes, and the plate box, are heated by a fire underneath, until the soot is burned off and ceases to adhere; if the driver is then moved upwards, it will diminish the space at the top of the air vessel, and enlarge that at the bottom equally which causes a portion of air to pass downwards through the plate box into the heated part of the vessel, being there heated and expanded it is more than sufficient to occupy that space, and is forced out at the port.
On the contrary, when the driver is moved downwards, a quantity of air is made to ascend through the cooling apparatus in the plate box, and being cooled and contracted, it is insufficient to occupy the increased space at the top, and a quantity of air must enter by the port to restore the equilibrium. One of these air vessels being placed at each end of the working cylinder of an air engine, is set in motion by the foregoing expanding and contracting of the air.

The claim is to:

  1. The employment of strips or rods of glass for receiving and imparting heat, during the passage of air from the hot to the cold chamber, and vice versa.

  2. The formation of the glass, iron, or other materials employed for this purpose, into continuous plates, strips, or rods of considerable length having their contiguous surfaces so placed as to make all the passages for the air narrow and in a line parallel, or nearly so, with the axis of the plate box or driver.

  3. The mode of constructing air engines, whereby the air, in passing from the heated end of the air vessel to the cool end thereof, it caused to pass first amongst an extensive system of surfaces to give off heat thereto, and then to pass amongst an extensive cooling apparatus, cooled by the passage of fluids, whereby the air in returning from the cool end of the air vessel to the heated end thereof, is caused to pass through the same extensive system of surfaces, and having taken up heat from those surfaces, to pass into the heated end of the air vessel.

  4. The use or application in air engines of cupped leather collars around the piston rods, or other rods, which communicate with the interior of the engine, by which means the air is enabled to be confined at a high pressure.