ENGINE STARTING SYSTEMS

In this chapter, we will discuss the operating principles of starting systems used with internal-combustion engines. As an Engineman, you will be concerned with four types of starting systems: (1) electric, (2) hydraulic, (3) air motor, and (4) compressed air admission. Electric starting systems are used with gasoline engines and diesel engines used in small craft (boats). The hydraulic starting system is used where nonmagnetic or lightweight characteristics are required. The air motor system is used wherever practicable because it contains sturdier components and requires less maintenance. Air motors are used to start Alco, Detroit Diesel, and Caterpillar engines. The com-pressed air admission system is used on many larger engines, such as those manufactured by General Motors, Fairbanks-Morse, and Colt-Pielstick. For a diesel engine to start, it must turn over fast enough to obtain sufficient heat to ignite the fuel-air mixture. If the engine turns over too slowly, the unavoidable small leaks past the piston rings and past the intake and exhaust valves (4-stroke cycle engines) will allow a substantial amount of the air to escape during the compression stroke. In addition to a loss of pressure, the heat loss from the compressed air to the cylinder walls will be greater at low speed because of the longer exposure.

The escape of air and loss of heat result in a lower temperature at the end of the compression stroke. Therefore, there is a minimum speed at which the diesel must turn over before ignition will occur and the diesel will begin firing. The starting speed depends on the size and type of the engine, and the temperature of the air entering the cylinders.

After reading the information in this chapter, you should be able to describe the four types of starting systems and their methods of operation. You should also be aware of the devices that can be used to help a diesel engine start in cold weather. These devices are commonly referred to as starting aids.