STATIONARY AND PORTABLE GASOLINE ENGINES It is clear that if you want to develop power with an internal combustion engine and natural or artifi cial gas is not available, or if you want an engine of this type that you can move about, or that will move you about, you must have one that will burn some kind of liquid fuel.
Now gasoline for any one of a number of excel lent reasons is the ideal liquid fuel and hence, it is largely used for running stationary and portable engines up to 30 horsepower.
Stationary and Portable Engines sta tionary engine is, as everybody knows, one whose position after it is once set remains so, that is, it is intended to stay and run in a fixed place.
A portable engine is simply an engine of the sta tionary type which is mounted on skids or on a hand or horse-drawn truck, as shown in Fig. 36, so that it can be hauled about by some other power than its own and used wherever it may be needed.
Difference Between a Gas and a Gasoline En chief mechanical difference betwee4,..ai gas and a gasoline engine of the stationary type is that in the former gas is admitted directly into the cylinder of the engine without the use of any inter vening or accessory apparatus, while in the latter means must be provided for (1) storing the gasoline; (2) bringing it to the cylinder, and (3) breaking it up into a spray so that it will mix with air to form the fuel mixture.
Further, a gasoline engine is exactly like a gas en gine in that it has the same kind of inlet and exhaust valves, governor, ignition and oiling systems.
A hot-tube, or hot ball igniter must not be used on a gasoline engine, but any one of the electric igniters of the kinds described in Chapter II is well adapted to fire a gasoline fuel charge. In stationary gaso line engines the cylinder cooling systems used are identical with those employed with gas engines.
But for portable engines, a hopper, or iron box, is usually secured to the top of the engine and this holds the supply of water which is circulated by the thermo-syphon system as explained in the preceding chapter under the heading of Cooling Tanks.
How the Gasoline System Gasoline Supply Tank.—The tank that holds the supply of gasoline can be set either (1) above the engine when it is fed into the cylinder through the gasoline valve by gravity, or (2) below the level of the engine when it is pumped to the gasoline valve and is then drawn into the cylinder.
The Gravity Feed System.—For small engines the gasoline tank can be placed above the engine as shown in Fig. 87.
The Pump Feed System.—For larger engines the gasoline tank must be buried in the ground or placed in a brick-lined vault outside of the building con taining the engine.
To make the gasoline supply perfectly safe the tank must be below the level of the gasoline pump a foot or so, and it should be at least 30 feet away from the engine. The filler should project above the ground, and the gasoline cock in the pipe line which leads to the pump must be easily get-at-able. It is shown at A in Fig. 88.
The gasoline pump is of the ordinary plunger kind, like those used for pumping water, and it is worked by an eccentric on the camshaft, as shown at B. The piston rod of the pump has a handle at tached to it, so that enough gasoline to start the en gine can be pumped by hand should it be needed.
The pump draws the gasoline from the bottom of the supply tank into an overflow cup, that is, a small vessel which holds about a pint of gasoline and sets above the engine. The excess gasoline that is pumped into the overflow cup runs back to the tank through a return pipe. The gasoline flows by grav ity from the inside of the overflow cup to the gaso line valve.
The Gasoline Valve.—Numberless schemes have been devised to break up the gasoline into a spray and mix it with the right amount of air to make the fuel mixture.
For a stationary gasoline engine a very simple and satisfactory device for this purpose is to use a needles valve and set it into the casing of the fuel inlet valve just back of the valve head, as shown in Fig. 39.
A needle valve is merely a small tube one end of which is formed into a nozzle with a little hole in it. A small rod, or needle, with a tapering point, sets in the tube and can be adjusted so that the amount of gasoline flowing through the nozzle can be varied. The end of the needle valve tube that projects outside of the cylinder is connected to the overflow cup by a length of pipe.
The way the gasoline valve works is like this: when the fuel inlet valve opens the suction strike draws the gasoline from the overflow cup through the gasoline valve into the cylinder in a spray. The minute particles are vaporized by the heat when they readily mix with the air which is taken in by the air valve at the same time.
As the fuel inlet valve is controlled by the gov ernor in the same way as the gas inlet valve on a gas engine, just enough gasoline is taken into the cylinder to drive the engine under all conditions of load, be it light or heavy.