Gas and Petroleum Engines

by H. de Graffigny

Fig. 9.—Lenoir Gas Engine (second type).

Koerting-Lieckfeld motor.—The first of these motors was constructed in 1877, and was based on the Dugald-Clerk cycle. The original type has, however, been abandoned, and the firm of Brûlé et Cie. of Paris now construct these engines on the Otto system. All the moving parts are attached to a vertical frame of cast-iron (Fig. 10), the lower half containing the cylinder. The admission and exhaust valves are situated in front and near the base. The governor is of the centrifugal type and acts directly on the levers of the valves. The flame ignition makes it necessary to occasionally clean out the valves, but otherwise the motor has few drawbacks, and is very neat and compact. The consumption of coal gas for engines of 8 horse-power and upwards is about 800 litres per horse-power hour. The crank-shaft is placed horizontally across the top of the frame, and the cams acting upon the valves are rotated by a bevel gear enclosed in a case, driving a thin supplementary shaft on which they are placed. The motor is self-lubricating, and is also constructed as a horizontal gas engine.

Fig. 10.—Koerting-Boulet Motor.

Andrews’ motor.—The governing apparatus in this engine is exceedingly simple and ingenious, consisting of a weight fixed to an oscillating lever which controls the admission valve. The position which the weight takes up depends upon the rapidity with which the lever oscillates, and consequently upon the speed of the engine. If, therefore, the engine is running too fast or too slow the weight takes up a new position, and the effect upon the admission valve is to either slow down or quicken the speed. The gases are ignited by means of a tube kept red-hot by a gas flame. This engine possesses the special advantage of being self-starting, that is to say, it is not necessary, as in many other motors, to start the engine by giving the fly-wheel a few rapid turns by hand. The motor is stopped with the crank in a position slightly in advance of the point corresponding to ignition. The gas is allowed to enter by a small auxiliary valve, which closes after the first explosion. This volume of gas entering the cylinder mixes with the air already in it, forming an explosive mixture. This explosive mixture then begins to escape by similar automatic self-closing valves situated at the top of the red-hot ignition tube. Ignition takes place, and is communicated to the rest of the gas in the cylinder, closing the two small valves by the force of the explosion. The piston is therefore driven forward, and the energy of this combustion is sufficient to start the engine. It must be understood that this operation is only performed once at starting, for immediately afterwards the engine falls into its normal cycle of operations. Two fly-wheels are as a rule provided to ensure constancy of speed. The consumption of gas is as low as 580 litres per horse-power hour in the large units of 100 horse-power.

The Andrews gas engine is also constructed of a special type for consuming poor gas produced by the Dowson process, and gives very good results. As a rule, about 600 to 800 grammes of anthracite are necessary to produce one horse-power hour. In one particular plant generating electricity, the cost has been certified to be as low as one penny per kilowatt hour, including lubrication.

Fielding gas engine.—The characteristic point in these engines is the extreme simplicity of the valve gear, only one valve being ever subjected to pressure. Even in the small engines of this type all sliding valves are replaced by those of the spring pattern, in fact, the valve mechanism consists simply of two spring-valves, one of which fulfils two functions, controlling the admission and the escape of the gases. The two valves are moved by a double lever actuated by a single cam. The cycle is that of Dr. Otto. When the piston is starting on the return stroke after an explosion has taken place, the lever lifts one of the valves, and the products of the combustion escape into a circular space situated below. In the next forward stroke this valve is still further lifted, opening the admission port, while at the same moment the exhaust port is closed by the second valve; a new charge is therefore drawn into the cylinder. At the end of the admission stroke the valves are released by the lever, and the compression can now take place during the second return stroke. The movement causing the lifting of the valve continuously throughout one whole revolution is effected by means of a cam with two prominences on it, which act in succession on the lever. There is only one valve, therefore, which is subjected to pressure, and even this is well provided against risk of leakage by the second valve being placed behind it, acting as a double seating. A chamber is also provided in which the gases are first mixed, and this mixing is regulated by a second lever and a special valve. The governor is of the inertia type, and is attached to the upper side of the double lever. It consists of a straight rod with a ball at one end and a knife edge at the other, pivoted at its centre to the end of the valve lever. As this lever is thrown forward the knife edge strikes the end of the spring-valve admitting gas to the mixing chamber. If the speed is too great the sudden jerk on the ball at the other end of the knife edge causes it to miss the valve, and no gas is admitted till the speed is reduced to the normal number of revolutions per minute. This arrangement is very sensitive, and keeps the speed exceedingly constant. Mr. Fielding has constructed some large gas engines of 350 horse-power which are started by compressed air, this air having been previously stored up under pressure when the motor was stopping.

Niel motor.—As will be seen from Fig. 11, the valves are actuated by cams rotating on a supplementary shaft placed parallel to the cylinder. A pair of toothed wheels transmit the rotation of the crank to this valve-shaft, and it is arranged so as to give one rotation to every two of the crank. The cycle of operations is somewhat similar to the Otto cycle; gas is only admitted to the cylinder for two-thirds of the forward stroke, so that the compression on the back stroke is somewhat lessened. It is doubtful whether there is much advantage in this method, but the Niel motors have had a large sale, which is a sufficient proof of their good qualities.