U.S.C.G. Merchant Marine Exam DDE – Unlimited HP Q622 ...€¦ · Q622 Gas Turbine Plants...

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U.S.C.G. Merchant Marine Exam

DDE – Unlimited HP

Q622 Gas Turbine Plants

(Sample Examination)

of 23 Q622 Gas Turbine Plants

8/22/2019

Q622 Gas Turbine Plants U.S.C.G. Merchant Marine Exam DDE-Unlimited HP Illustrations: 7

Choose the best answer to the following Multiple Choice Questions.

1. Compared to other types of engines, what is the biggest advantage of a gas turbine engine?

o (A) Simplicity of the control circuits. o (B) Low power-to-weight ratio. • (C) Highest power-to-weight ratio. o (D) Simplicity of installation.

If choice C is selected set score to 1.

2. Why is the cycle efficiency higher in the intercooled-recuperated cycle as compared to a simple cycle gas turbine? Illustration GT-0026

o (A) The intercooler serves to increase the required high-pressure compressor power while the recuperator utilizes waste heat from the exhaust to decrease turbine inlet temperature.

o (B) The intercooler serves to reduce the required high-pressure compressor power while the recuperator utilizes waste heat from the exhaust to decrease turbine inlet temperature.

• (C) The intercooler serves to reduce the required high-pressure compressor power while the recuperator utilizes waste heat from the exhaust to decrease required fuel to achieve the turbine inlet temperature.

o (D) The intercooler serves to increase the required high-pressure compressor power while the recuperator utilizes waste heat from the exhaust to increase turbine inlet temperature.


3. What is the difference between an open cycle and a closed cycle gas turbine engine?

• (A) An open cycle discards the working fluid and a closed cycle retains the working fluid. o (B) A closed cycle heats the working fluid from an internal source and an open cycle uses an

external source for heating the working fluid. o (C) There is no difference because both use the same working fluid. o (D) An open cycle retains the working fluid and a closed cycle discards the working fluid.

If choice A is selected set score to 1.

4. Why is a gas turbine considered to operate on the Brayton cycle?

o (A) Combustion causes no increase in volume. o (B) Combustion causes large increase in pressure. o (C) Combustion causes an increase in total mass flow. • (D) Combustion occurs with no increase in pressure.

If choice D is selected set score to 1.


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5. The thermal energy added to the gas as it flows through the combustion section has what effect on the gas?

o (A) Decreases volume. o (B) Increases pressure. • (C) Increases volume. o (D) Decreases pressure.


6. The acronym CDP stands for which of the following?

o (A) Compressor Discharge Pyrometer. o (B) Coupling Disassembly Point. • (C) Compressor Discharge Pressure. o (D) Choke Down Point.


7. The acronym VSV represents which of the following?

o (A) Vibration shutdown valve. • (B) Variable stator vane. o (C) Vibration stator vanes. o (D) Variable speed valve.

If choice B is selected set score to 1.

8. Which of the following statements correctly describes force?

o (A) Force is a scalar quantity. o (B) Force is work in a unit of time. • (C) Force has magnitude and direction. o (D) Force is not a vector quantity.


9. Potential energy is defined as which of the following?

o (A) The energy a body possesses due to its motion. • (B) The energy a body possesses due to its position. o (C) A measurement in feet per second. o (D) A total pressure measurement.



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Q622 Gas Turbine Plants U.S.C.G. Merchant Marine Exam DDE-Unlimited HP Illustrations: 7 10. Thermal energy is the only form of energy that can be added to or removed from a substance. How

is thermal energy that is added to a substance stored?

• (A) In the form of internal energy. o (B) In the form of potential kinetic energy. o (C) In the form of mechanical energy. o (D) In the form of heat.


11. What is the term given to a process that occurs without a loss or gain of heat?

• (A) Adiabatic o (B) Exothermic. o (C) Endothermic. o (D) Isothermal


12. A compressor is operating at an inlet pressure of 14.7 (atmospheric pressure at the time of measurement) and a compressor discharge pressure of 123 psig. Calculate the absolute pressure ratio across the compressor.

o (A) 8.2:1 o (B) 8.4:1 • (C) 9.4:1 o (D) 10.5:1


13. A temperature of 32.5 degrees Celsius converts to approximately what temperature in degrees Kelvin?

• (A) 305.5 degrees K. o (B) 427.5 degrees K. o (C) 240.5 degrees K. o (D) 492.5 degrees K.


14. Which of the following statements is true regarding centrifugal compressors?

• (A) The centrifugal compressor is frequently used on small, low power turbines. o (B) The efficiency of a centrifugal compressor is greater than that of an axial compressor. o (C) Centrifugal compressors are complicated in design and heavy. o (D) The impeller of a centrifugal compressor has a radial inlet and axial discharge.



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Q622 Gas Turbine Plants U.S.C.G. Merchant Marine Exam DDE-Unlimited HP Illustrations: 7 15. What is the disadvantage of a dual-entry centrifugal compressor compared to a single-entry

centrifugal compressor?

o (A) The dual-entry compressor is larger in diameter. • (B) The dual-entry compressor utilizes a more complicated inlet ducting. o (C) The dual-entry compressor has a greater efficiency. o (D) The dual-entry compressor rotates at slower speeds.


16. Which of the following is the main advantage of a split-axial compressor case?

o (A) Stronger construction. o (B) Simpler to disassemble. • (C) Easier to repair and inspect. o (D) Cheaper to manufacture.


17. An axial compressor basically consists of which of the following?

o (A) Rotating pistons and stationary liners. o (B) A stationary impeller and a rotating diffuser. o (C) A rotating impeller and a stationary diffuser. • (D) Stationary vanes and rotating blades.


18. Two functions of the compressor stator vanes include which of the following?

o (A) Direct air flow to rotor blades at the correct angle and are shaped to maintain a constant velocity and produce a pressure increase.

• (B) Direct air flow to each rotor stage at the correct angle and deliver air to the combustor at the correct velocity and pressure.

o (C) Direct air flow to rotor blades at the correct angle and are shaped to cause a velocity increase and a pressure decrease.

o (D) Direct air flow to rotor blades at the correct angle and are shaped to produce a velocity increase and maintain a constant pressure.


19. What is the term used to describe the stationary vanes preceding the first stage of an axial compressor?

o (A) Variable inlet vanes. o (B) First stage stator vanes. • (C) Inlet guide vanes. o (D) Variable stator vanes.



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Q622 Gas Turbine Plants U.S.C.G. Merchant Marine Exam DDE-Unlimited HP Illustrations: 7 20. Which of the following statements is true concerning axial compressor disk-type rotors?

o (A) Rotor discs are held together by through bolts. o (B) Rotor consists of rings that are flanged to fit one against the other. o (C) Rotor is only suitable for low-speed compressors. • (D) Rotor discs are shrunk fit onto a steel shaft.


21. What is a compressor midspan shroud?

o (A) A method of securing stator blades. o (B) The center of a two-piece rotor blade. • (C) A brace built into the middle of a rotor blade for damping. o (D) A support for the tips of the stator blades.


22. Most GTE fuel nozzles have passages for all of the following EXCEPT __________.

o (A) primary fuel flow • (B) cooling water o (C) secondary fuel flow o (D) compressed air


23. A centrifugal flow gas turbine uses what type of combustion chamber?

o (A) double-annular • (B) can o (C) can-annular o (D) annular


24. In a gas turbine engine, the majority of the energy is added to the working fluid in which of the following components?

o (A) Power turbine. • (B) Combustor. o (C) High-pressure turbine. o (D) Compressor.



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25. How do the high-velocity high-temperature gases cause the gas turbine rotor to rotate?

o (A) By converting the high-velocity gas to low-velocity gas. o (B) By increasing the velocity of the gases. o (C) By creating a low-pressure area before the rotor. • (D) By transferring velocity energy and thermal energy to the turbine blades.


26. In the operation of a marine propulsion gas turbine, kinetic and thermal energy required to drive the main propeller shaft are extracted by which of the following?

• (A) Power turbine. o (B) Multi-stage compressor. o (C) Exhaust gas. o (D) Combustor.


27. What are the two principle functions of the turbine nozzle guide vanes?

o (A) Convert the potential energy of the hot gases into heat energy and direct the flow of gases to the turbine rotor blades.

• (B) Convert the heat energy of the hot gases into kinetic energy and direct the flow of gases to the turbine rotor blades.

o (C) Convert the heat energy of the hot gases into potential energy and direct the flow of gases to the turbine rotor blades.

o (D) Convert the heat energy of the hot gases into potential energy and direct the flow of gases to the compressor rotor blades.


28. What method is utilized to allow turbine nozzle blades to withstand high inlet temperatures?

o (A) Laser cooling o (B) Thermoelectric cooling o (C) Water cooling • (D) Air cooling



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29. To keep the exit pressures relatively constant across a HP turbine blade, which type of construction is generally utilized?

o (A) Rateau. • (B) Impulse-Reaction. o (C) Impulse. o (D) Curtis.


30. HP turbine blades are generally cooled by which of the following methods?

o (A) Cooling water entering the root and exiting the tip. o (B) Compressed air entering the tip and exiting the root. • (C) Compressed air entering the root and exiting the tip. o (D) Cooling water entering the tip and exiting the root.


31. In a single shaft, cold-end drive gas turbine, the power output speed has what relationship to the speed of the compressor?

o (A) It is in an inverse relationship through reduction gears. • (B) It is the same or in a direct relationship through reduction gears. o (C) It varies independently of compressor speed. o (D) None of the above.


32. What is the purpose of the spring in a lip-type oil seal?

o (A) To seal against maximum fluid pressure o (B) To prevent air from entering the sump o (C) To remove burrs and dirt from the shaft • (D) To keep the neoprene snugly fit around the shaft


33. What type of seal is used in the gearbox of a gas turbine engine?

o (A) Lip-type o (B) Fishmouth o (C) Labyrinth-Windback • (D) Carbon ring



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Q622 Gas Turbine Plants U.S.C.G. Merchant Marine Exam DDE-Unlimited HP Illustrations: 7 34. What type of starter is commonly used on smaller gas turbine engines?

o (A) Air turbine • (B) Electric o (C) Pneumatic o (D) Hydraulic


35. Which of the following components removes the oil from the transfer gearbox?

o (A) Duplex filter assembly o (B) Lube oil storage and conditioning assembly o (C) Air/Oil separator • (D) Lube and scavenge pump


36. What is the most common type of spark igniter used on a gas turbine engine?

o (A) Suppression gap o (B) Resistive gap o (C) Delayed gap • (D) Annular gap


37. How is the lube oil supplied to each bearing in a gas turbine engine controlled?

o (A) Regulating valve. o (B) Flow divider. • (C) Calibrated orifice. o (D) Lube oil pump.


38. The electrostatic vent fog precipitator removes oil mist from which of the following areas?

o (A) Synchronous self-shifting clutch o (B) Gas turbine engine • (C) Main reduction gear o (D) Lube oil storage tank



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39. When the main reduction gear lube oil system is secured, which of the following components maintains the air within the casing at less than 35 percent relative humidity?

o (A) Rehumidifier o (B) Reciprocator o (C) Precipitator • (D) Dehumidifier


40. As shown in the illustration, what is the purpose of pressurizing the main bearing lube oil sumps on a typical marine gas turbine? Illustration GT-0023

o (A) Assists in cooling the lube oil. o (B) Provides uniform lube oil distribution around the bearing. o (C) Increases lube oil penetration. • (D) Minimizes oil leakage from the rotor shaft.


41. The main lubrication system utilized by the gas turbine engine shown in the illustration is what type? Illustration GT-0017

o (A) Oil mist recovery sump o (B) Common drain sump • (C) Dry sump o (D) Wet sump


42. The lube oil system shown in the illustration, consists of which of the following sub-systems? Illustration GT-0024

o (A) Sump venting. o (B) Lube oil scavenging. o (C) Lube oil supply. • (D) All of the above.



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43. The bleed air surge relief valve differs from a normal relief valve in which of the following ways?

o (A) Opens completely at a specified lift pressure and closes immediately as soon as the pressure begins to drop.

• (B) Opens completely at a specified lift pressure and remains open until the pressure drops to a specified preset pressure.

o (C) Gradually opens at a specified lift pressure and closes immediately as soon as the pressure begins to drop.

o (D) Gradually opens at a specified lift pressure and remains open until the pressure drops to a specified preset pressure.


44. The fuel oil system of a gas turbine engine provides all EXCEPT which of the following?

o (A) Provides accurately metered fuel for combustion o (B) Acts as a hydraulic medium to actuate the fuel control • (C) Acts as a cooling medium for the lube oil cooler o (D) Controls the angle of the variable stator vanes


45. Assuming at least a 500 rpm for the input shaft speed from the power turbine, as shown in the illustration, the synchronous self-shifting (SSS) clutch used on marine gas turbine main propulsion gears, requires which of the following inputs or conditions to make engagement possible? Illustration GT-0018

o (A) Availability of low-pressure air to provide control air pressure for engagement. o (B) Availability of high-pressure air to provide clutch air inflation pressure. o (C) When the input shaft speed from the power turbine falls below the output shaft speed. • (D) When the input shaft speed from the power turbine rises to the output shaft speed.


46. How do you manually lockout an SSS clutch?

o (A) Remove the SSS clutch locking pawls. • (B) Using the special wrench provided. o (C) Using air pressure. o (D) Calculate the engagement speed of the SSS clutch.



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47. What feature is commonly used on articulated reduction gear arrangements for the correction of misalignment between the 1st reduction gear and the 2nd reduction pinions?

o (A) Torsion pads. • (B) Quill shafts. o (C) Fixed block pads. o (D) Locked train shims.


48. The purpose of the main reduction gear in a marine gas turbine propulsion installation is which of the following?

o (A) Transfer low-speed gas turbine rotation to high-speed propeller rotation. o (B) Reduce gas turbine speed to engage the clutch. • (C) Transfer high-speed gas turbine rotation to low-speed propeller rotation. o (D) Increase gas turbine speed to engage the clutch.


49. What is the purpose of the Controllable-Pitch Propeller (CPP) hydraulic oil power system?

o (A) Supplies high-pressure oil for both propeller blade actuation and stern tube sealing. o (B) Supplies low-pressure oil for propeller blade actuation and control oil for propeller pitch

control. o (C) Supplies low-pressure oil for both pitch control and stern tube sealing. • (D) Supplies high-pressure oil for blade actuation and control oil for propeller pitch control.


50. On most marine gas turbines used aboard ships, vibration sensors are identified as which of the following?

o (A) Resistance temperature detectors o (B) Frequency synthesizers • (C) Accelerometers o (D) Transducers


51. Which of the following is NOT a gas turbine auto shutdown parameter?

o (A) High exhaust gas temperature. • (B) High compressor discharge pressure. o (C) Module enclosure fire. o (D) Power turbine over speed.



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Q622 Gas Turbine Plants U.S.C.G. Merchant Marine Exam DDE-Unlimited HP Illustrations: 7 52. Compressor characteristics are normally summarized in the form of which of the following?

• (A) Compressor map. o (B) Straight line graph. o (C) Spread sheet. o (D) Venn diagram.


53. Which of the following are the principle factors that affect the performance of a gas turbine compressor?

• (A) Pressure ratio, air flow, rotational speed. o (B) Fuel flow, air flow, exhaust temperature. o (C) Bleed pressure, fuel pressure, exhaust temperature. o (D) None of the above.


54. All clock positions, engine references, and enclosure references apply to viewing the gas turbine engine shown in the illustration, from which of the following locations? Illustration GT-0017

o (A) Left side of the power turbine to the right side. o (B) Intake end, looking toward the exhaust end. • (C) Rear (exhaust end), looking toward the intake end. o (D) Right side of the compressor to the left side.


55. Routine water washing of the gas turbine compressor shown in the illustration, is usually performed while operating under which of the following conditions? Illustration GT-0017

o (A) At 25% power. o (B) At 75% power. o (C) At 100% power. • (D) With the starter motor drive.


56. When conducting a borescope inspection, you must be aware of all of the following factors EXCEPT which?

o (A) The limitations of your equipment. o (B) The inspection areas and ports. o (C) The internal reference points. • (D) The engineer’s experience.



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Q622 Gas Turbine Plants U.S.C.G. Merchant Marine Exam DDE-Unlimited HP Illustrations: 7 57. Which of the following wrenches should NOT be used while working on a gas turbine?

• (A) Adjustable wrench. o (B) Box wrench. o (C) Flare nut wrench. o (D) Crowfoot wrench.


58. If the lube oil scavenge temperature exceeds 300 degrees Fahrenheit on the gas turbine engine shown in the illustration, and reducing power does NOT bring the temperature within limits, the operator should do which of the following? Illustration GT-0017

o (A) Monitor the temperature while continuing to operate. • (B) Shutdown the engine and troubleshoot. o (C) Continue to reduce power on the engine. o (D) Continue to operate at the reduced power level.


59. Compressor surge is caused by which of the following factors?

o (A) Low ambient air temperature. • (B) Interrupted air flow. o (C) Increased demand for secondary air. o (D) Maximum fuel pressure.


60. On a vessel equipped with marine propulsion gas turbines, the operator’s initial response to a high vibration alarm should be which of the following?

o (A) Wait for the harmonic vibration to dampen out. o (B) Switch to the secondary channel to confirm the alarm. o (C) Change out the vibration transducer. • (D) Reduce the engine speed.


61. How can compressor stall be prevented?

o (A) Utilize a two-spool compressor rotor. o (B) Lowering the angle of attack on the front stages. o (C) Installing air bleed valves in the middle of the compressor. • (D) All of the above.



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Q622 Gas Turbine Plants U.S.C.G. Merchant Marine Exam DDE-Unlimited HP Illustrations: 7 62. Which of the following could cause compressor stall?

o (A) The angle at which the hot gases strike the turbine rotor blades is too high. o (B) Air flow over the lower foil section becomes turbulent and destroys the pressure zone. • (C) The angle at which the air strikes the compressor rotor blades is too high. o (D) The angle at which the air strikes the compressor rotor blades is too low.


63. What is the primary purpose of the diffuser and distributor on the GE LM2500 gas turbine?

• (A) To provide uniform air flow to the combustor o (B) To provide even temperature distribution at the compressor o (C) To provide uniform air flow to the turbine o (D) To provide uniform air flow to the compressor


64. Where are the carbon dioxide nozzles located in the GE LM2500 gas turbine enclosure?

o (A) Above the compressor. o (B) Above and below the combustor section. • (C) On the cross beam under the compressor front frame. o (D) On either side of the power turbine.


65. Which of the following components prevent(s) objects smaller than 1/4 inch from entering the GE LM2500 gas turbine?

o (A) Demister pads • (B) FOD screens o (C) Inlet louvers o (D) Centerbody


66. How is the HP turbine rotor of the GE LM2500 gas turbine cooled?

o (A) By an air to air heat exchanger • (B) By a continuous flow of compressor discharge air o (C) By the ship's service sea water cooling system o (D) By synthetic lube oil



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67. Marine GTE fuel oil systems, as shown in the illustration, require fuel oil shutdown valves to be_________. Illustration GT-0021

o (A) manually operated from MPCMS• (B) piped in serieso (C) piped in parallelo (D) piped in series-parallel


68. For the GE LM2500 gas turbine engine shown in the illustration, the HP turbine 1st stage nozzlevanes are cooled by which of the following? Illustration GT-0020

o (A) 8th stage compressor air.o (B) 9th stage compressor air.o (C) 13th stage compressor air.• (D) 16th stage compressor air.


69. For the GE LM2500 gas turbine shown in the illustration, the 9th stage bleed air is used for which ofthe following? Illustration GT-0017

o (A) Sump pressurization and cooling.• (B) Power turbine cooling.o (C) High-pressure turbine second stage nozzle cooling.o (D) Compressor balance piston cavity pressurization.


70. For the GE LM2500 gas turbine engine shown in the illustration, the 13th stage bleed air is usedfor which of the following? Illustration GT-0017

• (A) High-pressure turbine 2nd stage nozzle cooling.o (B) Power turbine balance piston cavity pressurization.o (C) Sump pressurization and cooling.o (D) Power turbine cooling.



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National Maritime Center

Serving Our Nation’s Mariners

11/1/2018

Adapted for testing purposes only from Gas Turbine Systems Technician (Electrical)

3/ Gas Turbine Systems Technician (Mechanical) 3, Volume 2

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Further reproduction prohibited without permission

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U.S.C.G. Merchant Marine Exam DDE – Unlimited HP Q622 ...€¦ · Q622 Gas Turbine Plants...

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