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Detailed  Operation  of  the  Governor - h1018v1_57
Engine  Protection

Mechanical Science Volume 1 of 2
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DIESEL ENGINE SPEED, DOE-HDBK-1018/1-93 Diesel Engine Fundamentals FUEL CONTROLS, AND PROTECTION Starting  Circuits Diesel  engines  have  as  many  different  types  of  starting  circuits  as  there are  types,  sizes,  and manufacturers of diesel engines.  Commonly, they can be started by air motors, electric motors, hydraulic motors, and manually.   The start circuit can be a simple manual start pushbutton, or a  complex auto-start  circuit.   But  in almost  all cases  the following  events  must occur  for the starting engine to start. 1. The start signal is sent to the starting motor.  The air, electric, or hydraulic motor, will engage the engine's flywheel. 2. The starting motor will crank the engine.  The starting motor will spin the engine at a high enough rpm to allow the engine's compression to ignite the fuel and start the engine running. 3. The engine will then accelerate to idle speed. When the starter motor is overdriven by the running motor it will disengage the flywheel. Because  a  diesel  engine  relies  on  compression  heat  to  ignite  the  fuel,  a  cold  engine  can  rob enough heat from the gasses that the compressed air falls below the ignition temperature of the fuel.   To help overcome this condition, some engines (usually small to medium sized engines) have glowplugs.  Glowplugs are located in the cylinder head of the combustion chamber and use electricity to heat up the electrode at the top of the glowplug.   The heat added by the glowplug is sufficient to help ignite the fuel in the cold engine.  Once the engine is running, the glowplugs are turned  off  and the  heat of  combustion is  sufficient to  heat the  block and  keep the  engine running. Larger engines usually heat the block and/or have powerful starting motors that are able to spin the engine long enough to allow the compression heat to fire the engine.  Some large engines use air start manifolds that inject compressed air into the cylinders which rotates the engine during the start sequence. Engine  Protection A diesel engine is designed with protection systems to alert the operators of abnormal conditions and to prevent the engine from destroying itself. Overspeed device - Because  a  diesel  is  not  self-speed-limiting,  a  failure  in  the  governor, injection   system,   or   sudden   loss   of   load   could   cause   the   diesel   to overspeed. An  overspeed   condition  is  extremely  dangerous  because engine failure is usually catastrophic and can possibly cause the engine to fly apart. ME-01 Rev. 0 Page 38







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