Figure 1-31.—Blower air intake system.Figure 1-30.-Glow plug.GLOW PLUGS.— Glow plugs (fig. 1-30) and theinjection nozzle are installed in the precombustionchamber of the cylinder head. The glow plug is turnedon when you turn on the ignition switch. On some equip-ment a light on the dashboard signals that the glow plugis cycling which signals you to wait between 15 to 30seconds before cranking the engine. The heat, createdby electrical resistance in the glow plug, heats the fueland air mixture. The heat generated by the glow plug andthe heat generated by compression allow the fuel to ignite.AIR INDUCTION SYSTEMSThe function of an air intake system is to supply thecorrect amount of air needed to increase the combustionand the efficiency of an engine. On a diesel engine, theair intake system cleans the intake air, silences the intakenoise, furnishes air for supercharging, and suppliesscavenged air in two-stroke engines.The three major components of the air inductionsystem are blowers, turbochargers, and superchargers.They may be of the centrifugal or rotary type, or theymay be gear-driven directly from the engine, belt orchain-driven, or driven by the flow of exhaust gasesfrom the engine.BLOWERSThe scavenging process, used in the two-strokecycle diesel engine, is simply a charge of air forced intothe cylinder by the blower. As this charge of air is forcedinto the cylinder, all the burnt gases are swept outthrough the exhaust valve ports. This air also helps coolthe internal engine parts, particularly the exhaust valves.1-22The blower shown in figure 1-31 provides theforced-air induction for the scavenging process. Tworotors are closely fitted in a housing that is bolted to theengine. The rotor lobes provide continuous and uniformdisplacement of air as the rotors revolve. Blower rotorseither have two lobes or three lobes, depending on thetype.TURBOCHARGERSThe four-stroke cycle engine uses two methods ofair induction: naturally aspirated and turbo charged. Thenaturally aspirated system depends on atmosphericpressure to keep a constant supply of air in the intakemanifold. The turbocharger is designed to force air intothe cylinder and aid in scavenging the exhaust gases.The turbocharger differs from the blower in that theturbocharger uses the energy of exhaust gases to drivea turbine wheel (fig. 1-32).The hot exhaust gases from the engine go throughthe exhaust inlet, across the turbine wheel, and out theexhaust outlet. The force of the exhaust turns the turbinewheel and shaft. This action rotates the compressorwheel (impeller) that is attached to the opposite end ofthe turbine shaft. As the impeller rotates, it draws air intothe housing. The air is then compressed and forced intothe intake manifold.SUPERCHARGERSSuperchargers are engine-driven air pumps thatforce the air and fuel mixture into the engine. They aremade in three basic configurations: centrifugal, Roots,and vane.
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