De La Vergne Machine Co. Diesel De La Vergne Machine Co. has been manufacturing oil engines of the low pressure and the semi-Diesel types for a number of years. In 1918 they brought out their Type FD engine, which operates on the true Diesel cycle. The engine, which appears in Fig. 15, is of horizontal design, and embodies the use of a very rugged frame. The camshaft is borne in bearings in front of the cylinder head and is driven by the longitudinal layshaft through bevel gears. The valves lie horizontally and are actuated by short cam levers. The fuel pump and governor, which are driven by the layshaft, are similar to those used on the De La Vergne FH engine and are the result of a number of years of experience.
American manufacturers, with but few exceptions, have adopted the four-stroke-cycle engine. In this they were undoubtedly influenced by the greater freedom from operating difficulties which this type possesses over the two-stroke-cycle. To the uninitiated it would appear that the two-stroke-cycle engine was simpler, due to the elimina tion of the admission and exhaust valves. However, the design calls for the incorporation of some form of scavenging air com pressor since an air charge must be used to force the burnt gases out the exhaust ports when the ports are uncovered by the pistorA. If the fuel consumption is to approach that of the four-stroke cycle, the scavenging air charge must enter the cylinder at the cylinder head in order that the scavenging be successful. '11 air ports are used, the eddy currents set up by the air as it enters the cylinder somewhat destroy its scavenging effect.
The two-stroke-cycle, chiefly on account of the lighter weight per horsepower, has been in favor in marine work. It has not won complete possession of this field, and at present the swing is strongly toward the four-cycle. For the small-powered boat 200 h.p. rating and for the large motorships calling for engines of 2000 h.p. of greater, the two-stroke-cycle engine is better adapted than is the four-stroke-cycle. This applies especially to submarine boats,,_ even though the latter engine is more popular in this field at the present time.
The Diesel Southwark Foundry and Machine Co. is manufacturing a two-stroke-cycle engine that is applicable both for stationary and marine work.
This engine, a cross-section of which is shown in Fig. 16, is of
vertical design and has cylinders ranging in number from four to eight, dependent on the horsepower rating.
The engine is provided with a base or crankcase, to which is bolted the vertical support for the cylinder. This cast-iron support is at one side only, the other side being supported by ten sion rods. This makes the engine frame very open when the steel guards are removed. The cylinder and water jacket are cast in one piece; this is not objectionable on cylinders 12 inches in diameter. Use. is made of a stepped piston, the differential cav ity being used for the scavenging air compressor and for air starting as well. Since this engine is quite different from standard designs, a brief description of the method of operation is included.
The starting air, at 200 lbs. pressure, which has been stored in an air tank, is admitted into the differential cylinder above the piston P2. This forces the piston downward, and the engine turns over. The engine is turned over twice with the air, and the fuel-injection mechanism is thrown into play. The cylinders are connected in pairs through the scavenging manifold M, while the cranks of the paired cylinders are set at 180 degrees. With the working piston of cylinder No. 1 at top-center a fuel charge is injected through the needle valve N. The piston is forced downward on the power stroke while the piston in cylinder No. 2 is moving upward on the compression stroke. The scaveng ing or stepped piston P2 of No. 2 cylinder is at the same time compressing its charge of air to a pressure of around 7 pounds gage. When the working piston in No. 1 cylinder has moved over 80 per cent. of its stroke, it uncovers the exhaust ports E, allowing the burnt gases to escape. At the same time the scavenging air ports D are uncovered, and the scavenging air from No. 2 scavenging cylinder flows up the passage A, through the valve V2, and into the manifold M, which connects with the air ports D. This air blowing into No. 1 working cylinder scavenges the cavity of the exhaust gases and fills the cylinder with a pure air charge. The same events occur in No. 2 cylinder on the next stroke since the scavenging cylinder of No. 1 has drawn in its air charge through the port G and muffler S when the downward movement of No. 1 piston uncovered the port G.