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CONSOLE  OPERATING  OVERVIEW
Chapter 7- Internal-Combustion Engines

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low-frequency  vibration  in  gas  turbines  makes them  preferable  to  diesel  engines  because  there  is less  noise  for  a  submarine  to  pick  up  at  long range. Modern production techniques have made gas turbines economical in terms of horsepower- per-dollar   on   initial   installation,   and   their increasing reliability makes them a cost-effective alternative  to  steam  turbine  or  diesel  engine installation.  In  terms  of  fuel  economy,  modern marine  gas  turbines  can  compete  with  diesel engines   and   may   be   superior   to   boiler/steam turbine  plants  when  these  are  operating  on distillate fuel. However,  there  are  some  disadvantages  to  gas turbines. Since they are high-performance engines, many   parts   are   under   high   stress.   Improper maintenance  and  lack  of  attention  to  details  of procedure  will  impair  engine  performance  and may  ultimately  lead  to  engine  failure.  A  pencil mark on a compressor turbine blade or a finger- print in the wrong place can cause failure of the part. The turbine takes in large quantities of air that may contain substances or objects that can harm  the  engine.  Most  gas  turbine  propulsion control   systems   are   complex   because   several factors   have   to   be   controlled,   and   numerous operating  conditions  and  parameters  must  be monitored.   The   control   systems   must   react quickly  to  turbine  operating  conditions  to  avoid casualties  to  the  equipment.  Gas  turbines  produce loud,  high-pitched  noises  that  can  damage  the human  ear.  In  shipboard  installations,  special soundproofing   is   necessary.   This   adds   to   the complexity  of  the  installation  and  makes  access for  maintenance  more  difficult. From  a  tactical  standpoint,  there  are  two major drawbacks to the gas turbine engine. The first is the large amount of exhaust heat produced by  the  engines.  Most  current  antiship  missiles  are heat-seekers, and the infrared signature of a gas turbine  engine  makes  it  an  easy  target. Countermeasures, such as exhaust gas cooling and infrared  decoys,  have  been  developed  to  reduce this  problem. The second tactical disadvantage is the require- ment for depot maintenance and repair of major casualties.  The  turbines  cannot  be  repaired  in place  on  the  ship  and  must  be  removed  and replaced by rebuilt engines if anything goes wrong. Here  too,  design  has  reduced  the  problem;  an engine   change   can   be   accomplished   wherever crane service or a Navy tender is available, and the  replacement  engine  can  be  obtained. SUMMARY This  chapter  has  given  you  some  basic information  on  gas  turbine  engines  and  gas turbine control systems. For a more in-depth look at  gas  turbines,  refer  to  Gas   Turbine   Systems Technician  (Mechanical)  3  &  2,   NAVEDTRA 10548-2. 6-20






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