the engine-shaft and the fly-wheel on the generator, to take up the variations in speed (Fig. 75). It is often found in practice that the ordinary belt-connection is sufficient to prevent the variation from being transmitted to the dynamo shaft, provided the latter carries a fly-wheel also. The fly-wheel may consist simply of a heavy flange cast on one side of the pulley. It is desirable in this case to have the belt, which may be an ordinary leather one, a little longer and slightly more slack than usual, in order that its elasticity and variation in sag may be sufficient to take up the impulses. Modern gas-engines run much more steadily than the early forms, so that trouble in this respect is less common, and in many cases they are directly connected to generators like steamengines. The Otto Gas-Engine was brought out by Dr. N. A. Otto in 1867. The original form was the Otto-Langen engine, which was very noisy, the piston being thrown upward with considerable violence by the explosion of the gas; and it was superseded by the Otto silent gas-engine." This type is manufactured by the Gasmotoren-Fabrik Deutz, at Deutz near Cologne, where it originated; and in this country at Philadelphia. 66 The action of these engines as well as that of other types operating on the Otto cycle, such as the Crossley, Westinghouse, and Nash engines, is similar for all and will be described in connection with Fig. 65. The Crossley Gas-Engine is the Otto type as manufactured in England by Crossley Brothers and in this country in connection with the Loomis-Pettibone gas apparatus already described. In the latter case they are being built in sizes from 50 to 1400 H.P., of the single-, double-, and four-cylinder forms. A doublecylinder American-Crossley engine of 650 brake H.P., illustrated in Fig. 64, is designed for driving an electric generator which is connected directly on the end of the shaft shown in front. The single-cylinder and double-cylinder engines are guaranteed to regulate satisfactorily when driving direct-current generators or 25-cycle alternators in parallel, and the four-cylinder type for 60-cycle alternators in parallel. The Westinghouse Gas-Engine is built in two-cylinder and three-cylinder types, the former from 10 to 85 H.P. and the latter from 35 H.P. up. A vertical section through one cylinder of the three-cylinder form is shown in Fig. 65, all three being exactly alike. There is a four-cycle operation in each cylinder which is therefore half single-acting, so that a working stroke occurs in every revolution with two cylinders, and for each two-thirds of a revolution with three cylinders. A shaft A carries the exhaust-valve cams and is driven by gearing from the main shaft at one-half the speed of the latter. The exhaust-cam of each cylinder works against a roller at the end of the guide-lever G. A long stem H projects downward from the exhaust-valve E and rests on the end of the lever G, the valve being held to its seat by the helical spring as shown. The shaft A carries another cam for each cylinder, engaging with a roller on the lever B acting through a vertical stem D on the lever C that actuates the inlet-valve J, also closed by a spring. There is also an ignition mechanism which, at the proper instant, breaks an electric circuit, producing a spark at the terminals of the igniter. The upper portions of the cylinders are waterjacketed, as indicated at PR. The gas and air enter the mixing valve-chamber by separate inlets, the proportionate amounts being adjustable, and the mixture passes through a distributing chamber to the port and inlet-valve J. In the position indicated the piston is on its downward stroke, the charge being previously ignited at maximum compression. At the end of this working stroke the exhaust-valve E opens and the spent gases are forced out by the upward motion of the piston. A fresh charge is then drawn through the inlet-valve J on the down ward stroke; it is compressed on the upward stroke, after which it is ignited, and so on. The governor of the Westinghouse gas-engine is of the flyball type and controls the areas of the ports through which the gas and air are admitted to the mixing-chamber. This variation of the gas-port area is effected by a cylindrical valve or shell turned by a hand-lever so as to uncover more or less length of port. A separate lever similarly controls the air-port, thus enabling any desired proportion of gas and air to be fixed. The governor merely alters the quantity of the charge, but not the quality of the mixture. Each of the two hand-levers carries a pointer moving over a fixed scale, so that they can be set or reset accurately. Westinghouse gas-engines are started with compressed air supplied by a small compressor that may be operated by hand if necessary, but is ordinarily belt-driven a few minutes a day to charge a storage-tank. One cylinder is temporarily converted into a compressed-air engine by altering the action of the valves, and after three or four revolutions the gas and air are drawn into and exploded in the other cylinder or cylinders; the compressed air is then shut off and the engine runs normally. |