An Adjustable Mixing this kind of a mixing valve a needle valve fits into the nozzle, so that the amount of fuel oil admitted into the cylin der can be regulated. The kind used on a Fairbanks Morse engine is shown in Fig. 58. The air is taken in through a separate inlet valve.
The oil vapor and the air mix in the chamber just above the valve, and the feel mixture then goes into the cylinder of the engine. The inlet pipe of the needle valve opens into an overflow cup, or fuel reservoir, as it is called, that is, the oil is pumped into the fuel reservoir from the supply tank, and when the oil reaches a certain level the surplus flows back into the supply tank.
The Fuel Injection. Nozzle and Fuel Injection Pump.—In large oil engines a fuel injection nozzle, see A and B in Fig. 59, is generally used, and this is screwed into the head of the cylinder.
The end of the nozzle has a very small hole in it, and the fuel oil is injected into the combustion chamber at the proper time by means of a fuel pump. The nozzle breaks up the oil into a spray, and this is the first stage in converting it into a fuel gas, the next and final stage taking place when the heat of the combustion chamber completely vaporizes it. The better made nozzles have a spring cut-off valve inside of them to prevent the oil from dripping into the combustion chamber after the pump stroke has been made which injects the oil through the nozzle.
The fuel injection pump is usually of the plunger and check ball type, as shown in Fig. 60.
The stroke of the plunger takes place when the piston of the engine is making the last stretch of its compression stroke, and as the combustion cham ber is the hottest at the end of the stroke the oil is made into a thoroughly dry gas, and hence but little carbon is left behind.
The Use of Water in Oil Engines.—In some oil engines, especially those built in the larger sizes, a spray of water is sucked, or is injected, into the cylinder with the fuel charge.
To break up the water into a spray a nozzle is used, and the size of the orifice, as the hole in the end of it is called, is usually controlled by means of a needle valve exactly like those used for converting fuel oil into a spray. Of course, the instant the
spray of water enters the hot cylinder it is changed into live steam.
The scheme of using water in most oil engines is to soften the force of the explosions, when it acts in part like a steam engine, that is, it makes the expansive force more continuous. In engines where a igniter is used a spray of water injected into the cylinder prevents the fuel charge from ex ploding prematurely, that is, before the piston has reached the end of its compression stroke, and this it does by keeping down the heat of the cylinder. A water spray is not needed for this purpose where an electric ignition system is used.
Another good feature about using a water spray is that it helps to change the oil into a gas, and when the steam comes in contact with the white-hot parti cles of carbon a chemical change takes place and water gas, or producer gas, as it called, is made.
Now water gas is formed of two gases, namely, carbon monoxide and hydrogen, and both of these burn, hence the carbon is used up in making them, and this prevents it from being deposited in the cyl inder, where it scores the walls of the latter, makes the engine knock, back fire and lose power.
The bad thing about using a water spray, espe cially in small engines, is that it leaves a deposit in the combustion chamber if it is hard water. This untoward condition can be prevented by using rain water or distilled water. Again, where a water spray is used in a small engine the wear is very hard on both the cylinder and the piston, and this shortens the life of the engine. Finally, where a water spray is used the exhaust pot and exhaust pipe get clogged up with sediment, and it must be kept clean or the engine will not give its full rated horsepower.
Binds of Ignition kinds of igni tion schemes are used for firing oil engines, and these are (1) the igniter, or a modification of it, and (2) the electric system.
The Hot-Ball Igniter.—Engines that are fitted with hot-ball igniters are called engines, because the heat for firing the fuel charge is devel oped by the heat of the burning charge after the ball is heated by a gas, or a kerosene burner.