Engines Ch2

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Engines Ch2
2012-04-23 23:21:12
API 12 25

Chapter 2 Questions
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  1. 1. What is the purpose of the engine inlet?
    Acts as a diffuser and provides a turbulent-free supply of air to the face of the compressor.
  2. 2. Why should the inlet duct be constructed with a straight section?
    smooth out turbulent airflow
  3. 3. What are the advantages of a single-entrance duct?
    Simplest and most effective at providing smooth airflow.
  4. 4. What is the shape of a subsonic inlet duct? Why?
    Divergent. Decrease V increase P
  5. 5. What is the shape of a supersonic inlet duct? Why?
    >< (c/d) decrease V increase P
  6. 6. What is the purpose of a variable geometry inlet duct?
    To allow a supersonic aircraft to fly in all flight regimes (ss and subsonic)
  7. 7. What are the advantages and disadvantages of a centrifugal compressor? Of an axial flow compressor?
    • Centrifugal:
    • +: Rugged, low cost, good power output over wide range of RPMs, High pressure increases per stage
    • -: Large frontal area required, impratical for multiple stages
    • Axial Flow:
    • + High peak efficiencies, smal frontal area reduces drag, straight through flow allowing for high ram eff, combustion efff is better than centrifugal, with dual/twin/split starting flex is greater, improved high alt performance.
    • - Low inlet speed=>compressor stall, narrow rotational speed for good eff, high cost, difficult to manufacture, high starting power requirements.
  8. 8. What are the parts of a centrifugal compressor and what is the function of each?
    • Impeller: +V, P, Pt
    • Diffuser: -V,+P
    • Manifold: route air mass to burner
  9. 9. What are the components of an axial flow compressor?
    Rotors, stators
  10. 10. Why do rotor and stator vanes within an axial compressor decrease in length from the front to rear of the compressor?
    The cross sectional area decreases within the compressor from fore to aft to allow the velocity to remain fairly constant as pressure increases. Therefore, the rotor and stator length requirements will decrease.
  11. 11. What do inlet and exit guide vanes do?
    Redirect the flow
  12. 12. What is the function of the diffuser?
    • final -V
    • and +P
    • before combustion.
  13. 13. Describe a dual-spool axial flow compressor. Why is it used?
    Two separate compressors, driven by its own turbine, to obtain higher compressor ratios.
  14. 14. Where is fuel introduced within a gas turbine engine?
    In the burner.
  15. 15. What is the criteria for a good burner section?
    • MInimum pressure loss.
    • High combustion efficiency
    • Flame must not blow out
    • Contain the total combustion process
  16. 16. What are the three types of combustion chamgers? What are the advantages and disadvantages of each?
    • Can- ease of maintenance, cause cold spots on engine.
    • Annular- even heat, complicated maintenace.
    • Can-Annular- even heat, ease of maintenace, expensive
  17. 17. What is primary and secondary air?
    • Primary air = 25% mixes fuel for combustion
    • Secondary air=75% cooling and flame control
  18. 18. What is the purpose of the turbine section?
    To turn the compressor and accessories.
  19. 19. How much of the energy produced is used to turn the compressor and accessories?
    75% of the total heat energy produced prior to the turbine section.
  20. 20. What are the main parts of the turbine?
    Stators and rotors
  21. 21. What is creep?
    Turbine blade elongation and deformation
  22. 22. What is the purpose of the exhaust duct?
    To increase velocity and decrease turbulence.
  23. 23. Describe a subsonic and supersonic exhaust duct and how each operates.
    • Subsonic- convergent>, supersonic c/d ><
    • Both will maximize the increase in velocity at the expense of pressure.
  24. 24. Describe the four parts of an afterburner.
    Spray bars, flame holder, screech liner, variable exhaust nozzle.
  25. 25. Describe how an afterburner operates.
    Secondary air from burner section along with bypassed air (turbofan) is mixed with fuel and ignited in the afterburner duct to augment thrust.
  26. 26. What controls the amount of thrust augmentation an afterburner will produce?
    The more fuel introduced, the more thrust produced.
  27. 27. What is the function of the spraty bars? The flame holder?
    Spray bars spray fuel. Flame holders hold the flame and they create local turbulence (eddies) to enable a better fuel/air mixture for combustion.
  28. 28. What is a screech liner and how does it operate?
    It acts as a shock absorber to guard against pressure fluctuations or cyclic vibrations sometimes associated with AB.
  29. 29. What type of exhaust nozzle is used on an afterburner equipped aircraft?
    Exhaust nozzle.