Practical Hand Book of Gas, Oil and Steam Engines / Stationary, Marine, Traction; Gas Burners, Oil Burners, Etc.; Farm, Traction, Automobile, Locomotive; A simple, practical and comprehensive book on the construction, operation and repair of all kinds of engines. Dealing with the various parts in detail and the various types of engines and also the use of different kinds of fuel.

by John B. Rathbun

(60) Gnome Radial Two Stroke Motor.

The builders of the famous Gnome four stroke cycle rotary motor, Sequin Frères, have recently developed a radial two stroke cycle motor that bids fair to supplant their original type. Referring to the diagrammatic cross-sections which show only a single cylinder unit, a very long tubular piston will be seen that is divided into two independent chambers, A and B. Both chambers are placed in communication with the outside space, C and D.

The upper end of the piston is continued above the top division head of the chamber A, and the extension is provided with the slot F. Near the center of the piston, the walls of the piston are run out into a flat circular plate or trunk piston E, which is the actual piston head that receives the force of the explosion. The piston E reciprocates in the large cylinder H, which is reduced at its upper end to the diameter of the main piston barrel, for which it affords a sliding support, or guide, and also serves to aid the exhaust port closure. The lower end of the cylinder H is enlarged in diameter as shown by K so that a clear annular space is left between the cylinder walls and the piston head E, when the latter is at the bottom of the stroke. The cylinder diameter is then reduced to the diameter of the main piston barrel.

The motor operates as follows:

Suppose the piston to be ascending (Fig. 1), compressing the mixture above the piston head in the cylinder E, and at the same time the volume of the space M, below E, is being increased until the piston reaches the position shown in Fig. 2.

Fig. 65. Gnome Rotary Two Stroke Motor Diagram. Diagrams 1 and 2.

Referring to Fig. 1; the interior chamber A of the piston is in direct communication through the holes C with the space M, consequently as the piston goes up, a partial vacuum will be formed in these two chambers. When the piston reaches the top of its stroke as shown in Fig. 2, the holes D in the lower end B of the piston are uncovered as they rise into the increased diameter of the cylinder, and therefore the mixture is sucked in from the crank case until the chambers A and M are filled to atmospheric pressure.

The spark now occurs at the plug S, and the explosion takes place, driving the piston downwards as shown by Fig. 3, just before the exhaust takes place. The volume of the chamber M has now been decreased with the result that the mixture will have been compressed into the chamber A.

In Fig. 4, the piston has now reached the bottom of the stroke, and the ports F have opened as the slots carry below the upper end of the cylinder where the bore is increased. At the same time, as the piston plate E passes the bottom of the cylinder H into the enlarged diameter K, the compressed mixture in A and M rushes through the annular space opened around E into the combustion chamber and drives out the residual burned gases which still remain after the explosion. On starting the second revolution the piston rises and the cycle repeats as shown by Fig. 1.

Gnome Rotary, Diagrams 3 and 4.

This engine may be built with any number of the cylinder units described, preferably with an uneven number, as in the case of the Gnome radial four stroke cycle, and with twice the number of impulses of the four stroke type a very uniform turning movement should be had.

Fig. 64-b. Roberts Two Stroke Aero Motor Using a Rotating Tubular Valve that Controls the Mixture from the Carburetor so that it Enters Only One Crank Case at a Time. This Gives Each Cylinder an Equal Charge of Gas.

Fig. 64-c. Roberts Distributor Valve. The Ports Are Cut in the Valve so that Only One Crank Case is in Communication with the Carburetor at Any One Time. The Central Hole Connects with the Carburetor.

Since the valves are the parts that give the most trouble in the four-stroke cycle Gnome, this motor should be better adapted for aviation than the original type of Gnome.