Unit 5: Combustion Chambers - Practice Quiz

1 Which is a common type of gas-turbine combustion chamber?

2 Which combustion chamber uses several separate cylindrical flame tubes?

3 In which type of combustion chamber does combustion occur in one continuous ring-shaped space?

4 Which characteristic is desirable in a gas-turbine combustion chamber?

5 Why is a uniform combustor outlet-temperature distribution desirable?

6 Which design requirement allows a combustor to operate over a broad range of fuel-air ratios?

7 What is the main function of the primary zone in a gas-turbine combustor?

8 What happens to fuel before it burns effectively in a conventional gas-turbine combustor?

9 What is the main purpose of dilution air near the combustor exit?

10 Combustion efficiency indicates how completely the combustor converts fuel energy into what form?

11 Which observation generally indicates good combustion performance?

12 What does the combustor pattern factor describe?

13 What is a likely result if the fuel-air mixture becomes too lean?

14 How does a higher combustor-inlet air temperature generally affect fuel ignition?

15 Which operating condition can reduce the time available for combustion?

16 Why must the flame tube be cooled?

17 Which flame-tube cooling method forms a protective layer of air along the hot wall?

18 What type of flow region helps stabilize a flame inside a combustor?

19 Why is swirling air commonly introduced into the primary zone?

20 What is the primary purpose of a flame holder?

21 A small gas turbine requires combustion liners that can be removed individually without dismantling the entire combustor assembly. Which chamber type best meets this requirement?

22 An aircraft engine designer wants a compact combustor with low frontal area and a relatively uniform turbine-inlet temperature distribution. Which configuration is most suitable?

23 What feature distinguishes a can-annular combustor from a set of completely independent can combustors?

24 Increasing combustor pressure loss can improve air mixing, but why is the allowable loss normally limited?

25 A combustor has inlet temperature , mean outlet temperature , and maximum outlet temperature . Using , what is its pattern factor?

26 A redesigned combustor is much shorter, but primary-zone velocity remains unchanged. Which problem is most likely if no other design changes are made?

27 Why is only part of the compressor delivery air admitted near the fuel injector in a conventional gas-turbine combustor?

28 A fuel injector begins producing significantly larger droplets while all other conditions remain unchanged. What is the most likely immediate consequence?

29 What is the main function of dilution air introduced near the downstream end of a gas-turbine combustor?

30 The theoretical temperature rise for complete combustion is , while the measured rise is . Assuming constant specific heat and negligible heat loss, what is the approximate combustion efficiency?

31 A combustor receives air at a total pressure of and has a total-pressure loss of . What is the combustor exit total pressure?

32 Two combustors have equal combustion efficiency and pressure loss. Combustor X has a lower outlet pattern factor than combustor Y. What practical advantage does combustor X provide?

33 If combustor inlet temperature increases while pressure, reference velocity, and fuel-air ratio remain similar, which effect is generally expected?

34 For a fixed combustor geometry and unchanged inlet density, air mass flow is increased. Which combined effect is most likely?

35 During high-altitude operation, combustor inlet pressure falls while inlet temperature and reference velocity remain approximately constant. What is the likely effect?

36 In film cooling, why is relatively cool air introduced through liner slots or small holes?

37 The film-cooling effectiveness is . If , , and , what is the liner-wall temperature ?

38 How does a strong swirler help stabilize a flame in a gas-turbine combustor?

39 A stable combustor suddenly experiences flame blowout after airflow is increased without increasing fuel flow. What is the most direct explanation?

40 A designer increases the blockage area of a bluff-body flame holder. Which trade-off should be expected?

41 A high-bypass turbofan requires minimum combustor frontal area, low liner surface-to-volume ratio, and a highly uniform turbine-entry temperature profile. Modular replacement of individual burning zones is not a priority. Which chamber classification best satisfies these requirements?

42 A combustor must fit inside a common annular casing but retain separately developed flame tubes that can be inspected or replaced by sector. Cross-ignition between neighboring zones is also required. Which classification is most appropriate?

43 Compared with an equivalent straight-through combustor, what is the principal system-level trade-off of selecting a reverse-flow combustion chamber for a small gas turbine?

44 A combustor diffuser must produce a low primary-zone velocity from a high-velocity compressor discharge. Increasing the diffuser area ratio causes boundary-layer separation and a distorted dome inflow. Which redesign most directly addresses the problem while preserving substantial diffusion?

45 During redesign, air is transferred from the dilution zone to the primary zone while total airflow and fuel flow remain fixed. Which consequence best captures the resulting design trade-off?

46 A combustor has inlet temperature , mean exit temperature , and maximum circumferential exit temperature . Using , what is its pattern factor?

47 The overall fuel-air ratio of a combustor is , but only of the total air enters the primary zone. If the stoichiometric fuel-air ratio is and all fuel is initially admitted to the primary zone, what is the primary-zone equivalence ratio?

48 Under conditions where droplet evaporation follows the law, an injector change doubles the representative initial droplet diameter without changing gas properties. How does the characteristic evaporation time change?

49 Which sequence correctly describes how a rich-burn, quick-quench, lean-burn combustor limits thermal while completing combustion?

50 A combustor receives of air and of fuel with . The measured mean stagnation-enthalpy increase of the combined exit flow relative to the inlet air is . Neglecting fuel sensible enthalpy, what is the combustion efficiency?

51 A combustor has loss coefficient . At its inlet, , , and reference velocity is . Using air as an ideal gas with , approximately what percentage of inlet pressure is lost?

52 At fixed combustor geometry, inlet pressure, and mass flow, the inlet temperature is increased. Which statement most accurately describes the competing effects on flame stability?

53 Fuel temperature falls sharply during high-altitude operation, increasing viscosity while injector pressure drop and geometry remain nearly fixed. What is the most likely combustor response?

54 Suppose inlet temperature, equivalence ratio, atomization quality, geometry, and flow residence time are held fixed while combustor pressure increases. If the characteristic chemical time decreases, which nondimensional interpretation is correct?

55 A liner is exposed to gas at and receives cooling air at . If cooling effectiveness is , what liner-wall temperature is implied?

56 For the same total coolant flow, a liner is changed from a few discrete normal holes to many closely spaced inclined effusion holes. Which result is most likely when the holes are properly designed?

57 A stabilized flame initially operates at Damköhler number . Mass flow is increased by at unchanged density and geometry, so the characteristic residence time varies inversely with velocity. What chemical-time change would preserve the original ?

58 A swirler stabilizes a gas-turbine flame without a conventional solid bluff body. Which mechanism is principally responsible?

59 For a bluff-body flame holder, which local condition most directly indicates resistance to blowoff as velocity is increased?

60 An afterburner uses a fixed V-gutter flame holder. If approach velocity doubles while density, geometry, and loss coefficient remain approximately unchanged, how do wake residence time and absolute pressure loss scale?