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Compressor
Stator element of turbine assembly

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engines that have a centrifugal compressor. The annular and can-annular types are used on axial- flow   compressors. The  combustion  chambers  have  presented  one of  the  biggest  problems  in  gas  turbines.  The extreme  stresses  and  temperatures  encountered  are not   experienced   in   other   types   of   internal- combustion  engines.  The  liners  are  subjected  to temperatures  as  high  as  4000°F  in  a  matter  of seconds. The  combustion  chamber  must  operate  over a wide range of conditions. It must withstand high rates of burning, have a minimum pressure drop, be  light  in  weight,  and  have  minimum  bulk. The  inner  and  outer  liners  or  shrouds  are perforated with many holes and slots throughout their length. Air is admitted through these holes to protect the liner and to cool the gases at the chamber  outlet. The  through-flow  passages  are  used  in practically   all   modern   engine   combustion chambers.  In  the  through-flow  path,  the  gases pass  through  the  combustion  section  without  a change  in  direction. The  annular  combustor  liner  (fig.  6-18)  is usually  found  on  axial-flow  engines.  It  is  probably one  of  the  most  popular  combustion  systems  in use.  The  construction  consists  of  a  housing  and liner. On  large  engines,  the  liner  consists  of  an undivided circular shroud extending all the way around the outside of the turbine shaft housing. A large one-piece combustor case covers the liner and is attached at the turbine section and diffuser section. The dome of the liner has small slots and holes to  admit  primary  air  and  to  impart  a  swirling motion for better atomization of fuel. There are also  holes  in  the  dome  for  the  fuel  nozzles  to extend  through  into  the  combustion  area.  The inner  and  outer  liners  form  the  combustion  space. The outer liner keeps flame from contacting the combustor case, and the inner liner prevents flame from  contacting  the  turbine  shaft  housing. Large  holes  and  slots  are  located  along  the liners  to  (1)  admit  some  cooling  air  into  the Figure 6-18.—Combustor liner. combustion  space  towards  the  rear  of  the  space to help cool the hot gases to a safe level, (2) center the flame, and (3) admit air for combustion. The gases  are  cooled  enough  to  prevent  warpage  of the liners. The space between the liners and the case and shaft  housing  forms  the  path  for  secondary  air. The  secondary  air  provides  film  cooling  of  the liners and the combustor case and shaft housing. At  the  end  of  the  combustion  space  and  just before the first-stage turbine nozzle, the secondary air  is  mixed  with  the  combustion  gases  to  cool them enough to prevent warping and melting of the  turbine  section. The  annular-type  combustion  chamber  is  a very  efficient  system  that  minimizes  bulk  and  can be used most effectively in limited space. There are  some  disadvantages,  however.  On  some engines,  the  liners  are  one-piece  and  cannot  be removed  without  engine  disassembly. Turbines In  theory,  design,  and  operating  characteristics, the turbines used in gas turbine engines are quite similar to the turbines used in a steam plant. The gas  turbine  differs  from  the  steam  turbine  chiefly 6-12






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