Gas and Petroleum Engines

by H. de Graffigny

Forest gas engine (Fig. 4).—This motor, being of the single-acting type without compression, had at one time a considerable sale, being used where only a small power was required. The rectilinear motion is changed into a rotary one by means of an Oliver Evans beam, and a connecting rod which returned alongside of the cylinder to the crank-shaft and fly-wheel, which are placed at the back. Ignition is obtained by a burner which is re-lit by a smaller one at each stroke, and the cylinder is cooled not by a water jacket but by a helical groove, which increases the surface. This helix is formed by a thin plate cast on the cylinder. The fuel consumed was about 1400 litres of gas per horse-power hour, which may be considered good for such an engine.

Fig. 4.—Forest Motor.

Economic motor.—Constructed in New York. This engine is another example of the early attempts to obtain economy without compression. As a rule they were not constructed of more than half horse-power size, and the general arrangement is ingenious, but rather more complicated than those which we have so far spoken of. The piston rod is guided by being attached to one end of a lever, connected with crank by means of a vertical connecting rod. The cylinder is grooved, and cooled by the circulation of the air round it, and constancy of speed is obtained by a centrifugal governor, which cuts off the supply of gas when the speed is too high. The engine seems to have given some very fair results.

Lentz gas engine.—It is difficult to conceive a more simple mechanism than is to be found in this motor. The supply of gas is drawn into the cylinder by an open valve, and a gas flame situated in this admission port ignites the explosive gases. The force of the explosion closes the admission valve, and on the return stroke a cam opens an exhaust port situated underneath the cylinder. There is no water jacket, but the cylinder is formed of two parts connected together by a non-conducting joint. In order to smooth down the jerk of the explosion the head of the connecting rod slides in a groove, and is kept pressed against the crank-pin by a spring, the result being that the connecting rod is longitudinally elastic and deadens the shock of the explosion.

Group II., Class I.—One cycle per revolution.

Dugald-Clerk gas engine.—In the ideal motor we should have at least one explosion per revolution of the fly-wheel, which is not the case in the Otto cycle. For this reason many inventors have tried to construct gas engines with one cycle per revolution, but experience has taught us that though they may be mechanically more simple, they lose in efficiency what they gain in simplicity, and in spite of many eminent inventors attempting to solve the problem. Even the best-designed motors of this type have been unable to hold their own against the Otto cycle because they are not as efficient.

The first attempt was made by Dugald-Clerk in 1881. His engine is simple in the extreme, containing no gear-wheels, and working steadily and noiselessly at a fairly constant speed (Fig. 5).

There are two cylinders of equal diameter placed side by side, and projecting over the end of a cast-iron bed-plate. The first of these is the motive cylinder in which the explosion takes place; the other is used for compressing the explosive mixture, this compression taking place in the Otto cycle in the motive cylinder itself.

This secondary cylinder also serves for another purpose; it draws in a certain volume of air directly after the explosion, which is afterwards driven through the motive cylinder, effectively clearing out the waste gases. The advantage which this arrangement of double cylinders has over the Otto cycle, lies in the fact that one explosion can take place during each revolution of the crank, and consequently such very heavy fly-wheels as are used for the Otto type of engine are not necessary. The great disadvantage which the Dugald-Clerk motor possesses is the extreme suddenness of the explosion, which is practically complete before the piston begins to move. In spite of this defect the machines have a fairly high efficiency. The gases are ignited by a gas-jet situated in a sliding valve. A water jacket is used for cooling the cylinder, and in some of these motors a mechanism is attached for converting the engine from simple to compound. The compression cylinder then becomes double-acting, and the gases are further expanded in what was previously the motor cylinder only.