Gas and Petroleum Engines

by H. de Graffigny

Campbell gas engine.—The mechanism of this engine is very much like that of the Dugald-Clerk motor, two cylinders being placed side by side. The utilization of the heat is, however, far superior, and only about 500 litres of coal gas per horse-power hour are required. A result which the inventor of this type of cycle never succeeded in obtaining, but as far as we know the motor has never had any official trial, and the above figures are only taken from the makers prospectus. However, there is only a hardly perceptible shock from the explosion, and the motor can be safely recommended to anybody requiring a silent gas engine. There still exist gas engines worked on this same cycle per revolution principle, such as the Conelly, Day, De Ravel motors, descriptions of which must be sought elsewhere. The limited space at our disposal prevents us from discussing all those types which have only obtained a very small measure of success. The only remaining engine based on this principle worth mentioning is the Bénier motor, which is exceedingly instructive, but we shall speak of it later under the head of poor-gas engines. We shall at present pass on to the consideration of engines based in principle on the patent of Beau de Rochas, and first practically realized in 1877 by Dr. Otto.

Otto gas engine (Fig. 7).—The principle on which this engine is based is known as the Otto cycle, named after Dr. Otto, but first suggested by Beau de Rochas. Since the patents have expired numerous copies and imitations have been brought out, but very few surpass or even equal some of the earlier types.

Fig. 7.—Otto Gas Engine.

The explanation of the working of the Otto motor, which we are about to give, will save us from returning to it in the descriptions of analogous types brought out after this famous system. The cylinder is continued in a backward direction so as to form a compression chamber, into which the mixture of gas and air is drawn during the forward stroke of the piston. The mixture is compressed during the return stroke in this chamber, the pressure rising at the end of the stroke to about 3 or 4 atmospheres. At this point in the cycle a flame is brought into contact with the compressed gases and they explode. This explosion raises the temperature of the gases to 1500° C., and drives forward the piston under a pressure of about 150 lbs. to the square inch. During the second return stroke, corresponding to the latter half of the second revolution of the crank, the piston drives out the products of the combustion into the air under a pressure of about an atmosphere. The heating of the cylinder is avoided by keeping water automatically circulating through a jacket surrounding it. This is necessary, because if the cylinder walls became heated, the oil upon them would become decomposed, and lose its lubricating properties. Dr. Otto paid special attention to the efficiency of the engine, and in order to increase it, he diluted the air and gas drawn into the cylinder with a portion of the gases already burnt in the previous stroke. Consequently the explosion at the beginning of the stroke is less violent, and the gases continue burning while the piston moves forward. The cause of this slow combustion has been wrongly attributed to stratification of superimposed layers of gas and air, but it is probably due to the action of the cylinder walls.

The Otto gas engine is a marvel of simplicity from a mechanical point of view, very much more so than a Corliss steam engine for instance. The admission and exhaust valves are worked by cams, and the ignition takes place under pressure. The governor is sometimes of the centrifugal type, and at others of the inertia type, but in both it is a case of all or nothing, the supply being completely shut off if the engine is going too fast. The connecting rod joins the crank to the piston rod by a cross-head running into a bored out-guide. It is necessary to have a heavy fly-wheel, because, as only one explosion takes place per two revolutions, the fly-wheel must store up enough energy during that explosion to carry it through the rest of the cycle. Many different types of Otto gas engines now exist, some having two cylinders and a single crank, and others two fly-wheels, in order to ensure constancy of speed for driving dynamos. Dr. Otto devised a compound gas engine, but it did not succeed, and also a cheaper vertical type (Fig. 8), which is very convenient for small workshops. Since the invention of carburetted air the creator of the Otto cycle has devised another motor for use with gasoline instead of coal gas.

Otto devised the first practical gas engine and opened up the path for others, who, following in his footsteps, have confined their attention to improvement of detail. Some have undoubtedly succeeded, and by avoiding waste of heat, and by raising the initial temperature of the gases, they have considerably reduced the consumption of fuel. We shall now discuss different types of motors which have appeared during the last fifteen years, confining ourselves to the really successful ones.

Fig. 8.—Otto Gas Engine (vertical type).

Second Lenoir motor.—Twenty-five years separated the appearances of the first and second Lenoir motors, and during this time M. Lenoir gained a great deal of practical experience, so that if reference be made to Figs. 1 and 9 they will be seen to have very little in common. In the later type the cylinder projects over the back of the bed-plate, and is provided with deep circular grooves on the outside to increase the cooling surface. Ignition is obtained by the spark from a coil supplied by a battery as in the early form. The consumption of gas is about 800 litres per horse-power hour. Later on we shall discuss a petroleum motor for motor cars, and also a stationary petroleum engine by the same inventor. These engines were originally constructed by Mignon and Rouart, but later by the Compagnie Parisienne du Gaz, and are very well designed and constructed.