(D) Essential Mechanical Elements.— The power developed within the cylinder may be transmitted to the rotating shaft either accord ing to the turbine or the reciprocating engine principle. As, to-day, gas turbine power is not in practical use for internal combustion engines, the latter only will be considered. Fig. 18 il lustrates the mechanical elements of a single acting, horizontal gas engine.
In the cylinder, A, is a close-fitting trunk piston, B, a long open-ended piston, fitted with piston rings, B1, held in position in their grooves and prevented from revolving by means of small pins, placed at different position for each ring, so that the joints of the rings cannot work in line and allow the gases to blow past them. One end of the connecting-rod, C,, is held to the piston by the wrist pin, B., which is rigidly fixed in the body of the piston. The other end of the connecting-rod engages the E. The horizontal, straight-line movement of the piston is thus transformed, by the pendulum motion of the connecting-rod, C, into rotary motion of the crankshaft, F. On this crank shaft, which is supported by the main bearings, is fixed the flywheel, F, which gives the en gine a more regular and uniform motion. From the main shaft, F, by gear transmission, the essary and the piston and its rod must be cooled. All modern small and medium-sized engines are of the single-acting type. Only in such cases where the highest possible_cylinder capacity is required do manufacturers attempt to produce the double-acting engine. At the present time, the record capacity per cylinder of the double-acting two-cycle type is about 2,000 horse power; of the four-cycle, about 1,500 horse power.
(F) Multi-Cylinder Arrangements.— In the course of its development and branching out into the various fields of application, the in ternal combustion engine has been subjected to so many requirements and influenced by such factors as space, weight, uniformity of rota tion, economy, reliability and flexibility, that it appears to-day in many types, the best known of which are given in diagrammatic form fol lowing (Figs. 20 to 31).
In Fig. 25,a rather peculiar type is illus .
cam or timing shaft, G, is driven, and upon this shaft are fixed the cams, GI, for operating the inlet valve, H, and the exhaust valve, H,. The cam shaft also operates the magneto shown in Fig. 19, which, at the proper instant, produces a spark at the terminals of the spark plug, in the combustion chamber of the cylinder, A. Power is distributed from the gas engine to the shafting belt or rope trans mission from the flywheel, by geared drive from the main shaft, or by an electric generator may be mounted on an extension of the main shaft.
(E) Single- and Double-Acting Engines.—In a single-acting engine, Fig. 20, work is done at one end of the cylinder only, while the other, the crank end, is open and exposed to the sur rounding air, thus giving a cooling effect. The piston usually serves as a cross-head. In a double-acting engine, Figs. 23 and 24, work is done at both ends of the cylinder. Here a stuffing box and a separate cross-head are nec trated, the Oechelhauser-Junkers, single-acting, double-stroke, two-cycle engine. Two single acting, opposed pistons, work in one cylinder provided with inlet and outlet slots. A trans verse yoke and three connecting rods transmit the power developed in the cylinder to a three throw crank shaft, thus freeing the cylinder of all stresses but those to the radial action of the combustion pressures. Furthermore, the en gine is well balanced and therefore well suited for marine purposes.
It must be especially mentioned that the vertical, single-acting four-cycle, four and six cylinder,, all in line, Figs. 26 and 27, as well as the eight cylinder, Fig. 31, and 12 cylin der, Fig. 35, V-type, the latter occasionally called the twin six, have become the most pop utar engine types automobile, marine and aircraft practice. The reason for it is that these types give a more equal flow of power and weigh less per unit power than the one cylinder type. When the first automobiles in America were made, the gasoline engine used for propelling it was of the one cylinder, four cycle, horizontal, slow speed type, Fig. 20. The heavy vibrations due to the irregular torque caused discomfort to the passengers and damage to the vital parts of the engine and vehicle. To avoid this, automobile designers have grad ually adopted the vertical, high-speed, multi cylinder type, in which the power is obtained by high rotative speed rather than by large bore and stroke. To illustrate this, in Figs. 32, 33 and 34 the pressure-volume curves have been drawn for four-stroke cycle engines of one, four and six cylinders, respectively. From these curves it is evident that in the one cylinder type the power impulse is followed by a long idle period; in the four cylinder engine a small gap only remains, due to the early opening of the exhaust valve, while in the six cylinder type the torque curves overlap, thus causing a continuous flow of power with no periods of idling. This factor is a requisite in the opera tion of airplanes and very desirable in auto mobiles, since flexibility and performance of the motor is appreciated by any driver, espe cially in heavy traffic.