The Crankshaft and Flywheels.—This shaft, see M, changes the reciprocating motion of the connect ing rod into rotary motion. It usually carries two flywheels, one on each end, and these are made very heavy, which help to keep the speed uniform. The crankshaft also has a pulley and a spiral, or worm gear on it and the latter meshes with another spiral gear on the camshaft.
The Cam, or vertical and some horizontal engines the valves and igniter for firing the fuel charge are worked by a reciprocating rod, while in other horizontal engines the valves and igniter are operated by a rotating camshaft. It is shown at N.
This shaft is driven by the crankshaft through a pair of spur or spiral gears. A bevel gear is keyed to the shaft which drives the governor, and the cams on it work the gas and exhaust valves and the igniter.
A horizontal Otto gas engine assembled is shown in Fig. 21.
About the Gas Supply.—Since the gas does not flow into the cylinder in a steady stream, but by the intermittent suction of the piston, the supply pipe must be sufficiently large to deliver enough gas for each charge.
Not only this, but a rubber bag, as shown in Fig. 22, is connected in between the gas supply pipe and the gas inlet valve of the engine. This bag acts as a reservoir and supplies all the gas that is needed for each fuel charge. For a small engine the bag should be protected by a wooden box, but for a large engine it should be enclosed in an iron casing.
Kinds of Ignition Schemes.—There are two kinds of ignition schemes used on gas engines to fire the fuel charge and these are (1) the hot tube igniter and (2) electric ignition systems.
The Hot Tube Igniter.—This is a simple, but it is not a very safe, ignition scheme. It consists of a steel tube open at one end and closed at the other; the open end is fixed in the cylinder near the head so that the fuel charge can reach it, and it is kept white hot by the flame of a Bunsen burner.
The walls of the tube are about -2-6- inch thick, it has an outside diameter of about an inch, and a length of about 5 inches. An iron tube inches in diameter and lined with asbestos sets around the hot tube to prevent the loss of heat; a lot of little air holes are drilled near the lower end of the iron tube and just above them a pipe is screwed into it. This pipe is connected to a gas supply and
this provides the flame to heat the tube. The whole scheme is shown in cross-section in Fig. 23.
The way the hot-tube works is like this: the in stant the fuel mixture is compressed either an igni tion valve is opened by a cam on the camshaft or the piston slides off of a port or hole which opens into the tube. The fuel charge then rushes into the in candescent tube when it is ignited, and the flame sweeps back into the cylinder and fires the charge. This hot tube igniter is a very decided improvement over Barnett's ignition cock, which I described in the first chapter.
Kinds of Electric Igniters.—There are two kinds of electric ignition systems used on gas engines, and these are (1) the wipe spark, or make and break system and (2) the jump-spark system,.
Wipe Spark Igniters.—The Battery and Spark Coil System.—Likewise, there are two kinds of wipe spark igniters and these are (1) the battery and spark coil system and (2) the magneto system,.
Where a battery and spark coil is used the system is formed of four chief parts, namely, (1) the bat tery, (2) the spark-coil, (3) the igniter mechanism., and (4) the wipe spark electrodes.
The battery consists of half a dozen dry, Edison Lalande or storage cells. The spark-coil, or kick-coil as it is called, is the kind used for lighting gas jets, that is, it is made up of a single coil of No. 16 or 18 insulated copper wire wound on a soft iron core.
The purpose of this coil is to raise the voltage, that is, the pressure of the battery current, so that when the circuit is broken it will give a good hot spark. This the coil does by the action of the current on itself as it flows through the adjacent turns of wire, and the higher tension current thus set up is called the extra current.
The wipe spark electrodes consist of a fixed con tact point and a movable contact point, both of which are mounted on a flange; this is bolted to the head of the cylinder so that the electrodes are inside of the latter and the binding posts of the electrodes and the lever which works the movable electrode are out side of the cylinder head. The fixed and movable electrodes are well insulated from each other so that the current will not short circuit. The scheme is shown in Fig. 24.