Disc Engines.

Updated: 8 Dec 2008
Link added

The disc engine was was highly ingenious variation on the rotary engine. A disc rotated and wobbled- for want of a better word- in a closed chamber with the working fluid entering alternately on either side of the disc. Most people have some difficulty in visualising how this works- it's very much a 3D process.

THE DAKEYNE HYDRAULIC DISC ENGINE :1820s
In 1820-something (the exact date appears to be obscure) the mill-owners Edward & James Dakeyne commissioned a a hydraulic engine (aka a water engine) to make use of high-pressure water available near their factory site. The basic design was similiar to the Davie engine below, but with the shaft vertical.
For more details see this remarkable website: Dakeynes Disc (external link)
Regrettably that link appears to be out of action, for the time being at least. However, the main descriptive passage and the diagrams are now available at http://kmoddl.library.cornell.edu/biographies/Dakeyne/index.php.

THE STEAM DISC ENGINES

Left: Davie's Disc Engine: 1836.
"A disc b, is fixed to an oscillating shaft,a, which swings in a circuit pivoted in the disc crank,c. The cylinder heads are cones in the apex of which the ball bearing of the shaft oscillates. The outer shell of the cylinder,d, is spherical over which the disc moves. Steam enters alternately on either side of the piston." Through valves which are not shown, presumably? Or are no valves required, as in the Dakeyne engine?
This figure and the one below comes from "Mechanical Movements, Devices and Appliances" by Gardner D Hiscox, published by Sampson Low, Marston & Co in 1899. For each design the title, and the parts of the captions that are in quotes, are taken from the original book.

Left: Reuleaux Engine or Pump.
"A disc on a fixed shaft. The cylinder swings on a central spherical bearing, carrying an arm pivoted in a crank."
In this case the disc is fixed and the casing rotates around it; the opposite of the Davie engine above.
The name applied by Hiscox is misleading. Reuleaux certainly did not invent this engine, he merely analysed it in his book on kinematics.

Left: The Ericsson Engine: 1840.
Section from the side. Note the principle is not quite the same as the disc engines above. This engine was originated by John Ericsson, who was also involved in hot-air engines, and many other engineering endeavours.
An engine of this sort is believed to have driven the printing presses of the Times newspaper in London for some years. It is possible that it was particularily suitable for this job because the torque was more constant than that of a conventional piston-and-crank steam engine, but at the moment this is pure speculation.

Left: The Ericsson Engine: 1840.
Section looking from one end.
This engine was compared with The Tower Spherical Engine.