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Diesel Fuel Systems
Figure 1-32.-Turbocharger.

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Figure  1-31.—Blower  air  intake  system. Figure 1-30.-Glow plug. GLOW PLUGS.—  Glow plugs (fig. 1-30) and the injection  nozzle  are  installed  in  the  precombustion chamber of the cylinder head. The glow plug is turned on when you turn on the ignition switch. On some equip- ment a light on the dashboard signals that the glow plug is cycling which signals you to wait between 15 to 30 seconds  before  cranking  the  engine.  The  heat,  created by electrical resistance in the glow plug, heats the fuel and air mixture. The heat generated by the glow plug and the heat generated by compression allow the fuel to ignite. AIR INDUCTION SYSTEMS The function of an air intake system is to supply the correct amount of air needed to increase the combustion and the efficiency of an engine. On a diesel engine, the air intake system cleans the intake air, silences the intake noise, furnishes air for supercharging, and supplies scavenged air in two-stroke engines. The three major components of the air induction system are blowers, turbochargers, and superchargers. They may be of the centrifugal or rotary type, or they may be gear-driven directly from the engine, belt or chain-driven, or driven by the flow of exhaust gases from the engine. BLOWERS The scavenging process, used in the two-stroke cycle diesel engine, is simply a charge of air forced into the cylinder by the blower. As this charge of air is forced into the cylinder, all the burnt gases are swept out through the exhaust valve ports. This air also helps cool the  internal  engine  parts,  particularly  the  exhaust  valves. 1-22 The  blower  shown  in  figure  1-31  provides  the forced-air induction for the scavenging process. Two rotors are closely fitted in a housing that is bolted to the engine. The rotor lobes provide continuous and uniform displacement  of  air  as  the  rotors  revolve.  Blower  rotors either have two lobes or three lobes, depending on the type. TURBOCHARGERS The  four-stroke  cycle  engine  uses  two  methods  of air  induction:  naturally  aspirated  and  turbo  charged.  The naturally aspirated system depends on atmospheric pressure to keep a constant supply of air in the intake manifold. The turbocharger is designed to force air into the cylinder and aid in scavenging the exhaust gases. The turbocharger differs from the blower in that the turbocharger uses the energy of exhaust gases to drive a turbine wheel (fig. 1-32). The hot exhaust gases from the engine go through the exhaust inlet, across the turbine wheel, and out the exhaust outlet. The force of the exhaust turns the turbine wheel and shaft. This action rotates the compressor wheel (impeller) that is attached to the opposite end of the turbine shaft. As the impeller rotates, it draws air into the housing. The air is then compressed and forced into the intake manifold. SUPERCHARGERS Superchargers  are  engine-driven  air  pumps  that force the air and fuel mixture into the engine. They are made in three basic configurations: centrifugal, Roots, and  vane.







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