The hot-ball igniter consists of a hollow iron ball which sets in the head of the cylinder, as shown in Figs. 61, 62 and 68. To start the engine a cap, or plate, is taken off of the cylinder head, which exposes the hot ball and the latter is then heated by a gas, or a kerosene blow torch flame. When the ball is red-hot the blow torch flame is removed, the cap or plate is put on the cylinder head and the engine is started.
Now when the air is being compressed on the compression stroke it fills the hot ball and when it is fully compressed the fuel oil is injected into it and the hot air not only furthers the process of making a gas out of the oil but it fires the fuel charge as well.
The Hot Bonnet carbon collects in the ball and has to be cleaned out to prevent it from interfering with the ignition of the fuel charge, an improved form was devised. This was done by cutting away about half of the ball, which made a bonnet out of it, as shown in Fig. 61, at A.
The ignition bonnet is heated by a torch before the engine is started in exactly the same way as the ball igniter, after which the heat of the exploding fuel charge keeps it hot enough to ignite the following Jump Spark kinds of electric jump spark systems are used for firing the fuel charges of oil engines, and these are (1) the battery and jump spark coil with spark plug; (2) the rotat ing high. tension magneto with spark plug, and (3) the low tension oscillating magneto with make and break spark. All of these ignition systems have been explained in Chapters II and IV.
How the Governor Works.—With a small high speed oil engine whose crankshaft is coupled direct to the shaft of a dynamo and which is used only for charging storage batteries, a governor is not needed, but with oil engines that are used for running dif ferent kinds of machines where the load varies a governor is necessary.
Many oil engines whether small or large are fitted with govenors of the centrifugal shaft type, that is, there is a weight which is pivoted to the flywheel, as shown in Fig. 6.4. The flywheel is keyed to the crankshaft, and the inside part of the eccentric, or sheave, as it is called, is also keyed to the shaft; the strap of the eccentric, which is the outside part of it, is pivoted to the eccentric rod.
Now, when the engine is running and the flywheel gets to going too fast the weight which is lighter begins to move faster and catches up with the speed of the wheel. In so doing it moves the eccentric rod down, and this gives the eccentric rod a shorter throw, that is, a shorter to and fro movement.
Conversely, when the flywheel begins to slow down the weight cannot keep up with it, and this moves the eccentric rod up, which makes the throw of the ec centric rod longer. Having proceeded this far with the governor, let us see now how it controls the speed of the engine.
In small oil engines the eccentric rod of the gov ernor is connected with a butterfly valve which is pivoted in the inlet pipe that connects the fuel cham ber with the cylinder, as described in Chapter III. But in large oil engines the eccentric rod is coupled to the plunger rod of the fuel pump, as shown in Fig 65.
It is easy to see now that when the length of the throw of the eccentric rod is greater or lesser than normal the length of the stroke of the plunger of the fuel pump is varied so that when the engine tends to run too fast only a little fuel oil is pumped into the cylinder and when the engine begins to slow down a larger amount of oil is pumped into the cylinder.
Of course, there are a lot of little refinements in the governor, such as springs and dash pots to check the too sudden action of the weight, and adjust• menta on the pump, so that the speed of the engine can be varied by the engine tender while the engine is running. An oil engine with a governor and pump built on this principle not only makes the speed of the engine steady but is very economical of fuel. About Cooling Cylinders.—The only oil engine that I know of which is air-cooled is the little high speed Delco-light, all the others of whatever size and type, being water cooled.
In the first named a draft tube sets over the cylin der of the engine; the top of it is open and the lower part connects with a housing around the flywheel which is built like a fan. When the engine is run ning the fan sucks the air down through the draft tube and out into the open air.