Engineering Wonders of the World
Volume I

THE DEVELOPMENT OF THE GAS ENGINE. 217 in a gas-engine cylinder is now known as the “ Otto cycle.” Fig. 2 explains the exact meaning of the “ cycle,” which is made up of charging (or suction), compressing, firing (ignition), and exhausting strokes, repeated ad infinitum in this order. You will gather from the diagram that only one push is given to the piston in the course of two revolutions of the crank. The gas engine gets a good deal of work out of its fuel, as the fuel is actually enclosed in the cylinder. Fig. 3.—DIAGRAM OF CYLINDER AND PISTON OF A CLERK DOUBLE-ACTING ENGINE. Cooling the Cylinder. But so high is the temperature of combustion that the cylin- der must be surrounded by a jacket, through which water circulates to absorb and carry off the excess heat. (In the case of air- cooled engines, air performs the same function as the water of the jacket.) Of course, the sacrifice of heat means a great waste of energy, but this is an unavoidable evil. After the adoption of the Otto cycle, the gas engine grew in both popularity and size. The writer remembers being invited to see a large. engine of 16 h.p., which, he was assured, represented the economical limit. The second great advance in development dates from the time when Dugald Clerk cov- ered in the cylinder in front, so as to permit explosions on both sides of the piston, and thereby gain double power with very little increase of weight. Another equally important novelty was the introduction of separate gas and air pumps for driving the charge into the working cylinder, which no longer had to act as a pump. The two im- provements made it possible to get an im- pulse stroke every revolution of the crank— instead of one every two revolutions, as in the Otto cycle—in both directions, and so brought the gas motor almost into line with the double-acting steam engine as regards its steady turning action. Clerk did not reap any great advantage from his inventions, but The Gas “ Pro- ducer.” Dugald Clerk’s Im = provements. lived to see his ideas materialize in some of the best of the great gas engines of to-day. A sketch of a Clerk engine is given in Fig. 3. The fresh charges of air and gas entered the cylinder at c and c1 alternately, driving out the burnt charge through exhaust ports, e, and were compressed by the piston on its return stroke and fired at the dead point. Despite great improvements in design, pro- gress in size remained slow, as public lighting gas was the only fuel available. Now, this gas is manufactured to give light primarily, and its illu- minating qualities, though ex- pensive to obtain, are of no use in a gas engine. For this reason the big engine did not come along until a cheap fuel had been provided by the introduction of the “ poor gas ”—poor in hydrogen—producer. Fig. 5 shows a producer in section, a is a chamber lined with fire-brick, and fed with fuel —anthracite coal or coke—through a bell-top similar to that of a blast furnace. Most of the chamber is filled with incandescent fuel. Air, either forced by a pump or sucked by the engine, enters under the fire-bars and passes up through the fuel. Then chemical action commences, of incandescent carbon takes partner two atoms of oxygen, to form a molecule of car- bonic acid gas (C02), which is incombustible because the car- bon has got all the oxygen it requires. But further travel through the fuel causes each molecule to adopt another atom An atom to itself as Chemical Action in the “ Producer.