This cam turns with the shaft, and operates the kerosene oil pump. According to the position of the cam on the shaft, it will impart to the pump plunger a long or a short stroke, thereby injecting more or less oil into the cylinder. The lever pivoted on the bracket moves with the cam and is used for controlling the engine’s speed by hand. To stop the engine the handle of the lever is pulled towards the flywheel, thereby interrupting the pump action altogether.
The handle of the control lever can be fitted with an adjustable speed regulator when required. This device is for use on marine engines to enable the operator to slow down the engine. The speed regulator does not interfere with the action of the governor but acts in conjunction with it. Whatever the speed of the engine may be, it is under the control of the governor. The engine can be controlled from the pilot house if such an arrangement is desirable.
The fuel pump is made of bronze. The valves are made of bronze and are designed with very large areas. The plunger is made of tool steel. A bronze cup strainer is attached to the lower end of the pump to prevent sediment or foreign matter from reaching the pump valves. As a result of the care used in its construction, the fuel pump is not only very sensitive in measuring the oil required by the governor, but is also very strong and durable.
The nozzle through which the fuel is atomized into the cylinder is thoroughly water jacketed to prevent the formation of carbon within the nozzle. It is so constructed that the water jacket spaces and fuel spaces can be opened for inspection.
Lubrication of all the important bearing joints is effected by a mechanical force feed oiler, pressure feed oiler or by gravity sight feed oilers, depending upon the service for which the engine is designed. Oil is fed in this manner to the piston, the main bearings and the crankpin bearings. The oil for the crankpin is dropped from a tube into an internally flanged ring attached to the crank by which it is carried by centrifugal force to a hole drilled diagonally through the crank and crankpin to the centre of the bearing. This insures that all the oil intended for the crankpin shall reach it. This feature, as well as the use of the sight feed oiler itself, is in line with the best modern high speed engine practice, and is an important factor in the reliability of the engine.
CHAPTER VIII
IGNITION SYSTEMS
(73) Principles of Ignition.
It is the purpose of the ignition system to raise a small portion of the mixture to the combustion temperature, or the temperature at which the air and fuel will start to enter into chemical combination. When combustion is once started in a compressed combustible gas it will spread throughout the mass no matter how small the original portion inflamed. The rate at which the flame spreads through the combustion chamber depends upon the compression pressure, the richness of the mixture, the nature of the fuel and upon the number of points at which it is ignited.
In practice perfect ignition is seldom realized. This is due not only to the ignition system itself but to poor mixture proportions, imperfect vaporizing of the fuel, and low compression; all of which tend to a slow burning mixture with the attendant losses.
The best ignition system will be that which will cause the ignition to occur invariably at the point of highest compression and which will supply ample heat to start the process of combustion with a cold cylinder, imperfect mixtures, and low compressions. An efficient and reliable ignition system is without a doubt the most important unit in the construction of a gas engine. As ignition systems have improved and become more reliable, so has the gas engine become more widely used and appreciated, and in almost a direct proportion to these improvements.