DIESEL ENGINESDOE-HDBK-1018/1-93Diesel Engine FundamentalsAfter being filtered, the air is routed by the intake system into the engine's intakemanifold or air box. The manifold or air box is the component that directs the fresh airto each of the engine's intake valves or ports. If the engine is turbocharged orsupercharged, the fresh air will be compressed with a blower and possibly cooled beforeentering the intake manifold or air box. The intake system also serves to reduce the airflow noise. TurbochargingTurbochargingan engine occurs when the engine's own exhaust gasses are forcedthrough a turbine (impeller), which rotates and is connected to a second impellerlocated in the fresh air intake system. The impeller in the fresh air intake systemcompresses the fresh air. The compressed air serves two functions. First, itincreases the engine's available power by increasing the maximum amount of air(oxygen) that is forced into each cylinder. This allows more fuel to be injectedand more power to be produced by the engine. The second function is to increaseintake pressure. This improves the scavenging of the exhaust gasses out of thecylinder. Turbocharging is commonly found on high power four-stroke engines.It can also be used on two-stroke engines where the increase in intake pressuregenerated by the turbocharger is required to force the fresh air charge into thecylinder and help force the exhaust gasses out of the cylinder to enable the engineto run.SuperchargingSuperchargingan engine performs the same function as turbocharging an engine.The difference is the source of power used to drive the device that compresses theincoming fresh air. In a supercharged engine, the air is commonly compressedin a device called a blower. The blower is driven through gears directly from theengines crankshaft. The most common type of blower uses two rotating rotorsto compress the air. Supercharging is more commonly found on two-strokeengines where the higher pressures that a supercharger is capable of generatingare needed.ExhaustSystemThe exhaust system of a diesel engine performs three functions. First, the exhaust systemroutes the spent combustion gasses away from the engine, where they are diluted by theatmosphere. This keeps the area around the engine habitable. Second, the exhaust systemconfines and routes the gasses to the turbocharger, if used. Third, the exhaust systemallows mufflers to be used to reduce the engine noise.ME-01Rev. 0Page 16
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business