ROTARY STEAM ENGINE, a type of engines in which the pistons rotate within the cylinder, or the cylinder upon the pistons, thus giving a continuous rotary motion and eliminat ing the loss of power consequent to the neces sary change in the direction of motion of a i piston working horizontally in a cylinder, as in the case of an engine operating with a re ciprocating action.
The varieties of rotary engines are numer ous, consisting of machines equipped with one, two, three and four pistons on single axes, or of pistons working in pairs on several axes, operated by steam injected against them, or working by the reactive action of steam emitted tangentially. The basic principle was suggested by the inventors of the last century, among whom Watt, Cartwright and Galloway may be included; while among the notable engines of this class may be mentioned the Scheutz (Swedish), the Thompson (Scotch), the Behrens (American) and the Piriens and Hill (English), in all of which the pistons revolve within the cylinder and differ from each other only in the details of the mechanical arrange ments employed to utilize the pressure ,of the steam.
In another form perfected by Harris, por tions of the engine are attached to two hubs and run in different directions. The hollow din:o nions of one axis •carries the two radial arms which emit steam at their ends tangentially against vanes carried on the other axis with a direct driving action. By gearing the two mo tions are utilized upon a single shaft. The latest development, and perhaps the most effi cient, is that perfected by William M. Hoffman, of the type in which the cylinder revolves around the pistons upon an elliptical steam chest supported by a hollow shaft through which the steam is admitted and exhausted.
. Fig. 1 shows a side view of the Hoffman engine in which the shaft and core, or steam chest, are stationary and the cylinder revolves. Live steam is admitted at the left end of the hollow shaft and is utilized by the action of an automatic cut-off arrangement which allows it .to enter the expansion chamber from the sta tionary core, where it expands and pressing against a piston moves it forward over the el liptical surface of the core and in so doing causes the cylinder to revolve. As the piston
approaches the greater dimension of the ellipse, it is forced into its housing, where it forms an abutment against the escape of steam; while a piston in its housing on the opposite side of the cylinder arrives opposite the port of ex haust exhausts the steam, and, relieved of the pressure of the greater dimension of the ellipse, emerges from its housing, and forms the free side of a new chamber, into which the live steam is again admitted by the automatic cut off to expand and continue the action while steam is admitted to the shaft. The expansion chamber is so arranged that it has but three sides — the inner surface of the cylinder and the outer surface of the ellipse, both of which are rigid, and the convex surface of the pis tons, which are free to move in and out of housings in the cylinder casing.
The chief defects of this type of rotary en gine are the excessive loss of power by fnctios of the pistons against the core and the compli cated system of valves, steam ports, connecting arms, etc., which are difficult to keep in proper order. Many forms of rotary engine are en tirely free from valves and steam ports. The type illustrated in Fig. 2 uses the expansion of the steam in one long curve, for almost a com plete revolution of the rotor R. The pistons P slide in grooves in the rotor R and are pushed against the cylinder by helical springs. When steam is admitted it pushes the first piston ahead and with it the rotor until the next fol lowing piston is exposed to its action. Near the exhaust port the piston is pressed into its groove and as it passes the port the steam is exhausted.
Rotary engines are designed to obtain the greatest possible efficiency with the least amount of fuel consumption and a great reduction in engine-room floor space. Engines capable of developing 300 horse power at 2,000 revolutions per minute have been successfully and economic ally operated. W. MORE; Ja. C.E, Consulting Engineer.