The parts discussed in this chapter are those generally associated with the air systems of most engines. Some engines are equipped with parts that perform special functions. These parts, even though related to the engine air systems, are more frequently considered as parts of other engine systems.

For example, some engines are equipped with intake air heaters or use other methods to over-come the influence of low temperatures in cold weather starting. Devices and methods used for this purpose are discussed in chapter 10. Many engines are equipped with devices or systems which provide crankcase ventilation. Blower action is necessary in many ventilation systems. The systems operate to prevent contamination of engine-room spaces by heated or fume-laden air to reduce the formation of sludge in lubricating oil and to prevent the accumulation of combustible gases in the crankcase and in the oil pan or sump. Devices that serve to ventilate engine crankcases are discussed with the lubricating systems.

SUMMARY

In diesel engines, the passageway for air into the combustion spaces and burnt gases from the combustion spaces is formed by the parts of two systems-the intake and exhaust systems. The combustion spaces serve as the dividing line between these two systems.

The primary purpose of an intake system is to supply to the cylinders a large volume of air for combustion and scavenging. In addition, the system must clean the air and reduce the noise created by the air as it enters the engine. When the air has served its purpose in the cylinder, the waste gases are expelled to the atmosphere by the exhaust system. In the turbocharged engine, the waste gases serve to drive the turbocharger prior to the expulsion of the gases to the atmosphere by way of the exhaust system.

After studying the information in this chapter, you should understand both the purposes and the principles of operation of the components of the air and exhaust systems in an engine and be able to trace the path of the intake air and exhaust gases through the systems.

You should also be able to understand the significance of scavenging and supercharging and how these processes differ in the operating cycles of 2- and 4-stroke cycle engines. If you are uncertain in any of these areas, go back and review those sections of this chapter before preceding to the next chapter.

Figure 6-3.-Scavenging and supercharging in diesel engines.