Gas and Petroleum Engines

by H. de Graffigny

Fig. 5.—Plan of Dugald-Clerk Engine.

Owing to the fact that this motor was not as efficient as those of the Otto type it never became a commercial success, and it is doubtful if any are working at the present date.

Early Stockport gas engine.—The working of this motor affords a good example of British ingenuity. The compression cylinder is situated behind the motive cylinder, being a prolongation of it on the same axis; the two are firmly bolted together end on. The active piston is in front and connected to the crank, drawing behind it the piston of the compression chamber. Each cylinder has a separate sliding valve. The rear cylinder having aspirated and compressed a volume of the explosive gases, they are passed into the motive cylinder through a sliding valve which also serves to ignite them. The waste gas escapes into the air by a special valve. The aspiration and compression take place in the auxiliary cylinder once in every revolution of the crank, and besides, the motive piston also compresses the gases a trifle before the explosion takes place. The exhaust valve is made to open slightly before the piston reaches the end of its stroke. The motor was rather inefficient, and since its appearance a new type has been brought out with an Otto cycle which we will describe later on.

Benz motor (Fig. 6).—In this motor the inventor attempts to drive out the whole of the exhaust gases before the second half of the backward stroke of the piston is reached. To do this he injects a certain volume of air under pressure, driving out the burnt gases and substituting itself in their place. Before the end of this return stroke a small auxiliary pump introduces the requisite amount of coal gas, which is then compressed during the rest of the stroke. The ignition is effected by a small magneto machine driven by the engine itself, the sparks being generated between two fine metallic points in the cylinder. The jet of air required to drive out the product of the combustion is furnished from a reservoir, pressure in it being maintained by using the other side of the piston as an air-pump. This arrangement is an advantage, because cold air is being continually drawn into the cylinder which keeps it cool, and enables the lubrification to take place more effectively. There is also an external cooling apparatus in the form of a water jacket, which uses about 40 litres of water per horse-power hour, and keeps the cylinder at about 75° C. The Benz motor is very well known on the Continent, and much of its success is due to the fact that it seems to work as well with gasoline as with coal gas! It is constructed by M. Roger of Paris, and in consequence of the extreme constancy of its speed, it has been successfully applied to driving dynamos, and also to launches, motor cars, etc.

Fig. 6.—Benz Gas Engine.

Baldwin gas engine.—The cycle of this engine is somewhat similar to that of the Benz motor, one side of the piston being used for expansion and the other side for compression. Part of the bed-plate casting is arranged so as to form a reservoir for the compressed gases. The coal gas is also admitted into this vessel, so that it contains an explosive mixture. As the vessel is only made of cast-iron this arrangement is rather dangerous. There are three valves, the admission valve being regulated by the governor. The power developed is, therefore, always kept proportional to the demand, and the constancy of speed is sufficient to warrant the use of these engines for running dynamos for electric light. The ignition is by an electric spark, and is generally obtained from some extra apparatus, such as accumulators or batteries, and an induction coil. The engine is constructed by Messrs. Otis Bros. of New York.

De Ravel motors.—The first motor constructed by M. de Ravel was exhibited in Paris in 1878, and was of the oscillating cylinder type, with a variable centre of gravity. The explosion drove up a heavy piston whose rod was directly connected to the crank-pin. The revolution of the crank-pin caused the whole cylinder to move in the same manner as that of the early oscillating steam engines. This movement was used as a means of opening and closing the ports. The efficiency of the engine was low, using some 600 to 700 litres of gas per horse-power hour; and besides the motor had, owing to faulty mechanism, the unhappy knack of suddenly stopping dead. These defects caused M. de Ravel to abandon this type and to bring out a second motor in 1885, performing one cycle per revolution. This new motor only had one cylinder, whose rear half acted as a compression chamber during the backward stroke of the piston, whilst the explosion took place in the front end of the cylinder. The consumption of gas was slightly more than an Otto engine, and the motor ran exceedingly silently and evenly, but this advantage was not of much service in the struggle against the all-conquering Otto motor.

Midland motor (Taylor).—Constructed in Nottingham, this engine is of the horizontal double-cylinder type. One cylinder compresses the explosive mixture and passes it on to the other, where it is ignited and does work. The cranks connected to the two pistons are placed 65° apart, and a complete cycle in the cylinders is performed every revolution. The makers of this engine claim a consumption of only 600 litres of gas per horse-power hour.