SUMMARY - 14104

porcelain, and a side electrode connected to the shell. The side electrode is adjusted so that there is a small space (gap) between it and the center electrode. This gap varies depending on the engine. When the plug fires, an electric spark jumps across the gap between the electrodes. When the engine is running, the electric current in the primary circuit flows from the battery through the switch, the primary winding in the ignition coil, the breaker points, and then back to the battery. The high voltage is produced in the secondary winding in the ignition coil, then flows through the distributor to the individual spark plugs and back to the ignition coil through the engine frame. It is interesting to note that the high voltage that jumps the gap in the spark plugs does not come from the battery but is produced in the ignition coil. The ignition coil and the condenser are the only parts of the ignition system that require an explanation. The soft iron core and the primary windings function as an electromagnet. The current flowing through the primary windings magnetizes the core. The same core and the secondary windings function as a transformer. Variations in the primary current change the magnetism of the core, which in turn produces high voltage in the secondary windings. With the engine running and the breaker points closed, low-voltage current flows through the primary circuit. When the breaker points open, this current is interrupted and produces high voltage in the secondary circuit. The electricity, which would otherwise arc across the breaker points as they are separating, now flows into the condenser. The principal purpose of the condenser is to protect the breaker points from being burned. The condenser also aids in obtaining a hotter spark. The contact-point ignition system is an older type. The electronic ignition system is of the newer type. The basic difference between the contact- point and the electronic ignition systems is in the primary circuit. The primary circuit in the contact- point system is opened and closed by contact points. In the electronic system, the primary circuit is opened and closed by the electronic control unit. The secondary circuits are practically the same for the two systems. The difference is that the distributor, ignition coil, and wiring are altered to handle the higher voltage that the electronic ignition system produces. One advantage of this higher voltage of approximately 47,000 volts is that spark plugs with wider gaps can be used. This results in a longer spark, which can ignite leaner fuel-air mixtures. As a result, engines can run on leaner mixtures for better fuel economy and lower emissions. Another difference is that some electronic ignition systems have no mechanical advance mechanisms—centrifugal or vacuum. Instead, the spark timing is adjusted electronically. The starting system of the gasoline engine is basically the same as that of the diesel engine. The generator keeps the battery charged and provides the current to operate the lights and other electrical equipment. The starter motor draws current from the battery and rotates the flywheel and crankshaft for starting. SUMMARY This chapter was designed to give you a brief understanding of diesel and gasoline internal- combustion engines. You will find these engines on all ships in the Navy. It will be of great value to you to learn more about them by reading the referenced material given throughout this chapter. 7-14