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

(70) Elyria Semi-Diesel Type.

A type of semi-Diesel type oil engine has been recently developed by the Elyria Gas Power Co., Elyria, O., that presents many features of interest. It operates on the two stroke cycle principle, and with the exception of the spray nozzle has no valves in the working cylinder. The principle of the semi-Diesel type cycle as distinguished from the true Diesel engine, was described in Chapter III, as having the following characteristics. (1) Fuel injection. (2) Medium compression pressure. (3) Hot plate ignition. (4) An efficiency approximating that of the true Diesel type.

Fig. 77. Working Cylinder of Elyria Oil Engine.

It is claimed that the change from the ordinary four stroke cycle Diesel cycle has been accomplished with practically no loss of thermal efficiency, and that the elimination of the many moving parts of that type has done away with many of the operating difficulties. By the introduction of a false piston end and an unjacketed cylinder head, the loss of efficiency due to the lower compression is compensated by the reduction of heat loss to the jacket water. Because of the high temperature it is possible to burn the heaviest fuels with a maximum pressure not exceeding 400 pounds per square inch, and without trouble due to missed ignition at light loads. With a given cylinder capacity this heating effect has increased the output about 75 per cent. The loss due to the friction of the scavenging apparatus causes a fuel consumption of approximately 10 percent more than a standard four stroke Diesel.

Unlike the Diesel, this engine automatically controls the quantity of injection air admitted to the cylinder at different loads, the air corresponding with the amount of fuel injected. This is in marked contrast with the Diesel engine which admits a constant volume of air at all loads. In place of the usual crank-case compression of the scavenging air met with in the ordinary two stroke cycle engine, the initial compression in the Elyria engine is performed by a “differential piston” which acts in an enlarged portion of the cylinder bore. This construction increases the volumetric efficiency from 70 percent, in the case of the marine type, to well over 90 percent, and it also does away with the bad effect of the compression on the lubrication of the main crank shaft bearings.

Fig. 78. Compressor Cylinder of Elyria Oil Engine.

The working piston and differential piston as shown by Fig. 77 is separate castings fastened together by four studs, and the piston pin is carried by the differential piston which acts as a cross-head, taking all of the side thrust from the main piston. The working piston is easily taken from the cylinder by removing the cylinder head and the four nuts that fasten it to the differential piston casting. The displacement of the differential piston is approximately 1.9 times the displacement of the working piston which is more than enough for thoroughly scavenging the cylinder and supplying air for combustion. The air suction is controlled by a piston valve which eliminates much of the loss encountered in the marine type of two stroke cycle.

In the figure may be seen the separate or auxiliary piston head which is bolted to the piston proper, a construction that greatly increases the working temperature, and allows a symmetrical form of piston. By removing the cap over the inlet port, it is possible to inspect the condition of the six piston rings with removing the piston from the cylinder. Because of the clean burning of the fuel lubrication is easily effected by the force pump which supplies oil at three points around the cylinder wall.

Three stages of compression are employed for providing the air for fuel injection, the first stage being accomplished by the differential piston, and the remaining two stages by a separate air pump driven by an eccentric from the crankshaft. This cylinder also supplies the air for starting the engine, the air being taken from the second stage and piped to the storage tank. The suction of the second stage pump which receives its air from the differential pump (first stage) is controlled automatically so that it is possible to keep the supply tank at any desired pressure regardless of the pressure or amount of air used for the fuel injection. Air from the tank (at approximately 200 pounds pressure) is piped to the suction side of the third stage air pump. In this suction line is a valve, controlled by the governor, which regulates the amount of air admitted to the injection nozzle, and also the amount. This pressure at the nozzle will vary from 500 pounds per square inch to 1000 pounds depending on the load and the nature of the fuel. The high pressure air travels directly from the pump to the fuel valve casing, and is equipped with a safety valve and pressure gauge.

The fuel pump is driven by a Rites Inertia Governor located in the fly-wheel which varies the stroke of the pump plunger and gives a correct proportion of fuel to the load. This type of governor has been extensively used on high speed engines and is exceeding accurate. The fuel pump may be disconnected from the governor drive, and operated by hand when it is necessary to provide fuel for starting. The spray or injection valve is operated by a cam, which lifts the valve at the proper moment in a very simple manner. The valve proper is made of a single piece of steel with openings of ample size, so that there is no danger of clogging with the heaviest fuels. As the valve only lifts 1
16 of an inch, the amount of work required to operate the valve is very small.

Starting is accomplished by spraying cold gasoline into the cylinder through the fuel valve in the same manner that the heavier oil is fed during operation, and the ignition is performed by a high tension coil and batteries. No spark time device is used, so that a continuous shower of sparks is thrown into the mixture during the starting period. Within a minute after the engine is started, the ignition switch may be opened, the gasoline cut off, and the heavy oil turned on for continuous running on full load. Starting by an electric spark avoids the inconvenience and danger of torch starting with a retort.

Cooling water is admitted around the compressor cylinder from which point it goes to the working cylinder, and is there discharged. Less water is required for this type of engine than for the ordinary gasoline engine, for with the water entering at 60°F, only 3 gallons per horse-power hour is used. With fuel oil weighing 7.33 pounds per gallon the makers claim a fuel consumption of .65 pounds per horse-power at the rated load. The amount of cylinder oil used does not exceed 1 pint per 100 horse-power hours, while the loss of the bearing oil is extremely small because of the return system.