National Maritime Center

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1 National Maritime Center Providing Credentials to Mariners U.S.C.G. Merchant Marine Exam (Sample Examination) Page 1 of 23

2 Choose the best answer to the following Multiple Choice Questions. 1. Why is a gas turbine considered to operate on the Brayton cycle? o (A) Combustion causes large increase in pressure. o (B) Combustion causes no increase in volume. o (C) Combustion causes an increase in total mass flow. (D) Combustion occurs with no increase in pressure. 2. Which of the following components removes the oil from the transfer gearbox? o (A) Lube oil storage and conditioning assembly o (B) Air/Oil separator o (C) Duplex filter assembly (D) Lube and scavenge pump 3. 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 o (C) Transducers (D) Accelerometers 4. 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 5. The acronym CDP stands for which of the following? o (A) Choke Down Point. o (B) Coupling Disassembly Point. (C) Compressor Discharge Pressure. o (D) Compressor Discharge Pyrometer. Page 2 of 23

3 6. What type of air seal is used in the sump and turbine areas of a gas turbine engine? (A) Labyrinth-Honeycomb o (B) Lip-type o (C) Fishmouth o (D) Pneumatic carbon ring If choice A is selected set score to For the GE LM2500 gas turbine shown in the illustration, the 9th stage bleed air is used for which of the following? Illustration GT-0017 o (A) High-pressure turbine second stage nozzle cooling. o (B) Compressor balance piston cavity pressurization. (C) Power turbine cooling. o (D) Sump pressurization and cooling. 8. How is the lube oil supplied to each bearing in a gas turbine engine controlled? o (A) Regulating valve. o (B) Flow divider. o (C) Lube oil pump. (D) Calibrated orifice. 9. Which of the following is an advantage of a single-shaft gas turbine engine compared to a split-shaft gas turbine engine? o (A) Lower starting torque o (B) Reversible (C) Fewer moving parts o (D) Better fuel economy 10. Where are the carbon dioxide nozzles located in the GE LM2500 gas turbine enclosure? o (A) Above and below the combustor section. o (B) On either side of the power turbine. o (C) Above the compressor. (D) On the cross beam under the compressor front frame. Page 3 of 23

4 11. What is the term used to describe the stationary vanes preceding the first stage of an axial compressor? o (A) Variable stator vanes. o (B) Variable inlet vanes. (C) Inlet guide vanes. o (D) First stage stator vanes. 12. The electrostatic vent fog precipitator removes oil mist from which of the following areas? o (A) Lube oil storage tank (B) Main reduction gear o (C) Synchronous self-shifting clutch o (D) Gas turbine engine 13. How do the high-velocity high-temperature gases cause the gas turbine rotor to rotate? o (A) By creating a low-pressure area before the rotor. o (B) By converting the high-velocity gas to low-velocity gas. (C) By transferring velocity energy and thermal energy to the turbine blades. o (D) By increasing the velocity of the gases. 14. Why are loose-fitting blades used on the first several stages of large axial compressors? o (A) To compensate for a malfunctioning compressor support bearing. (B) To minimize vibration while the engine is passing through critical speed ranges. o (C) To compensate for the abrasive action of the blade tips. o (D) To maintain close tolerances in the compressor. 15. In the ignition system of a gas turbine engine, how is optimum spark achieved? o (A) Concentration of minimum energy in maximum time (B) Concentration of maximum energy in minimum time o (C) Concentration of maximum energy in maximum time o (D) Concentration of minimum energy in minimum time Page 4 of 23

5 16. Kelvin is the absolute temperature scale that corresponds to which of the following? (A) Absolute reading of a measured temperature in degrees Celsius. o (B) Absolute reading of a measured temperature in degrees Fahrenheit. o (C) Absolute reading of a measured temperature in degrees Rankine. o (D) None of the above. If choice A is selected set score to Which of the following are the principle factors that affect the performance of a gas turbine compressor? o (A) Bleed pressure, fuel pressure, exhaust temperature. o (B) Fuel flow, air flow, exhaust temperature. (C) Pressure ratio, air flow, rotational speed. o (D) None of the above. 18. 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 19. A turbine stage is represented by which of the following components and in which order? o (A) One set of rotating blades, one set of stationary vanes. o (B) One set of rotating vanes, one set of stationary blades. o (C) Two sets of stationary vanes, one set of rotating blades. (D) One set of stationary vanes, one set of rotating blades. 20. Power is defined as which of the following? o (A) Force applied through a distance. o (B) The rate of applying a force. (C) The rate of doing work. o (D) Work performed through a distance. Page 5 of 23

6 21. How many shock mounts are used to secure the GE LM2500 gas turbine enclosure to the ship's foundation? o (A) 16 o (B) 24 (C) 32 o (D) In order to get a ready indication for a normal start with a GE LM2500 gas turbine engine, what permissive(s) must be met? o (A) Bleed air valve must be closed. o (B) GG speed must be less than 1200 RPM and all engine trips reset. o (C) Fuel supply pressure must be greater than 8 psig. (D) All of the above. 23. An axial compressor stage is represented by which of the following components and in which order? (A) One set of rotating blades, one set of stationary vanes. o (B) One set of stationary vanes, one set of rotating blades. o (C) One set of rotating blades, two sets of stationary vanes. o (D) One set of rotating vanes, one set of stationary blades. If choice A is selected set score to For the GE LM2500 gas turbine engine shown in the illustration, the HP turbine 2nd stage nozzle vanes are cooled by which of the following? Illustration GT-0020 o (A) 9th stage compressor air. o (B) 13th stage compressor air. (C) 16th stage compressor air. o (D) Frame vent bleed air. 25. How do you manually lockout an SSS clutch? o (A) Remove the SSS clutch locking pawls. o (B) Calculate the engagement speed of the SSS clutch. (C) Using the special wrench provided. o (D) Using air pressure. Page 6 of 23

7 26. The lube oil system shown in the illustration, is designed to lubricate the main bearings by what principle? Illustration GT-0023 (A) spray lubrication with dry sumps o (B) totally submerged oil bath o (C) splash lubrication o (D) self-contained partial oil bath If choice A is selected set score to The primary function of an axial compressor rotor blade is which of the following? o (A) To use centrifugal force to increase the pressure of the air stream. (B) To impart acceleration to the air mass, resulting in an increase in velocity. o (C) To act as a diffuser to the air flow causing an increase in pressure with a resultant decrease in velocity. o (D) To change the direction of the air flow. 28. How is the HP turbine rotor of the GE LM2500 gas turbine cooled? o (A) By synthetic lube oil o (B) By the ship's service sea water cooling system (C) By a continuous flow of compressor discharge air o (D) By an air to air heat exchanger 29. The purpose of the metal spray rub coating on the rotor and stator casing of an axial type compressor is which of the following? o (A) control air flow through the compressor (B) provide close vane to rotor and blade to stator case clearances o (C) seal the circumferential dovetails o (D) ensure protection for the gearbox adapter when removing or replacing the bearings 30. On the gas turbine lube oil system shown in the illustration, air and oil are primarily separated in the air/oil separator through the use of which of the following? Illustration GT-0024 o (A) Filter (B) Impeller o (C) Heater o (D) Strainer Page 7 of 23

8 31. The acronym MFC represents which of the following? o (A) Manifold fuel control. o (B) Maritime fuel congress. o (C) Midframe compressor. (D) Main fuel control. 32. An open cycle gas turbine engine is best described by which of the following statements? o (A) Energy is neither created nor destroyed and the cycle is therefore perpetual. o (B) Energy is added externally. o (C) Working fluids are taken in, transformed, and then recuperated. (D) Working fluids are taken in, transformed, and then discarded. 33. The thermal energy added to the gas as it flows through the combustion section has what effect on the gas? o (A) Increases pressure. o (B) Decreases volume. o (C) Decreases pressure. (D) Increases volume. 34. What is the purpose of the Controllable-Pitch Propeller (CPP) hydraulic oil power system? o (A) Supplies low-pressure oil for both pitch control and stern tube sealing. o (B) Supplies high-pressure oil for both propeller blade actuation and stern tube sealing. o (C) Supplies low-pressure oil for propeller blade actuation and control oil for propeller pitch control. (D) Supplies high-pressure oil for blade actuation and control oil for propeller pitch control. 35. Which of the following statements is true regarding centrifugal compressors? o (A) The impeller of a centrifugal compressor has a radial inlet and axial discharge. o (B) The efficiency of a centrifugal compressor is greater than that of an axial compressor. (C) The centrifugal compressor is frequently used on small, low power turbines. o (D) Centrifugal compressors are complicated in design and heavy. Page 8 of 23

9 36. 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. o (B) Gradually opens at a specified lift pressure and remains open until the pressure drops to a specified preset pressure. (C) Opens completely at a specified lift pressure and remains open until the pressure drops to a specified preset pressure. o (D) Gradually opens at a specified lift pressure and closes immediately as soon as the pressure begins to drop. 37. The struts of the GE LM2500 compressor front frame provide passages for all of the following mediums EXCEPT which of the following? o (A) Scavenge oil (B) Fuel oil o (C) Seal-pressurization air o (D) Lube oil 38. What is the term given to the condition in which cyclic pressure changes result in a repetitive failure and recovery of compressor air flow? o (A) Laminar. o (B) Turbulence. o (C) Stall. (D) Surge. 39. What is the primary function of the main fuel control on the GE LM2500 gas turbine engine? o (A) To control fuel pump inlet pressure o (B) To control stator vane angle and bleed air discharge (C) To control stator vane angle and GG speed o (D) To control fuel temperature 40. Gas turbine fuel manifold pressure is established by which of the following actions? o (A) Closing the fuel recirculating valve. o (B) Starting the fuel service pumps on low-speed. (C) Rotating the gas generator. o (D) Starting the fuel service pumps on high-speed. Page 9 of 23

10 41. 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. 42. 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? (A) Quill shafts. o (B) Fixed block pads. o (C) Torsion pads. o (D) Locked train shims. If choice A is selected set score to Most GTE fuel nozzles have passages for all of the following EXCEPT. o (A) compressed air (B) cooling water o (C) secondary fuel flow o (D) primary fuel flow 44. 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. 45. Mechanical work is defined as which of the following? o (A) A measurement in pounds per square inch. o (B) Rate of doing work. (C) A force acting through a distance. o (D) Distance traveled over time. Page 10 of 23

11 46. Why is the cycle efficiency higher in the intercooled-recuperated cycle as compared to a simple cycle gas turbine? Illustration GT-0031 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 increase the required high-pressure compressor power while the recuperator utilizes waste heat from the exhaust to increase 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 reduce the required high-pressure compressor power while the recuperator utilizes waste heat from the exhaust to decrease turbine inlet temperature. 47. You are on watch on a gas turbine propelled vessel as shown in the illustration. After reducing power in response to a high lube oil supply temperature alarm, the temperature continues to increase. Your next step should be which of the following? Illustration GT-0017 o (A) Continue to reduce power. (B) Shutdown the engine. o (C) Water wash the engine. o (D) Check oil consumption. 48. What type of main reduction gear arrangement prevents independent axial and rotational movement of the pinions? o (A) Independent suspension (B) Locked train o (C) Unlocked train o (D) Hydraulic suspension 49. 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) Continue to operate at the reduced power level. o (B) Monitor the temperature while continuing to operate. o (C) Continue to reduce power on the engine. (D) Shutdown the engine and troubleshoot. Page 11 of 23

12 50. Borescope inspection of the combustor section requires which type of light source? o (A) 150 watt o (B) 500 watt (C) 1000 watt o (D) All of the above. 51. Compressor characteristics are normally summarized in the form of which of the following? o (A) Venn diagram. o (B) Straight line graph. (C) Compressor map. o (D) Spread sheet. 52. What type of engine starter motor is commonly found on the marine gas turbine shown in the illustration? Illustration GT-0006 (A) Hydraulic motor o (B) AC synchronous motor o (C) AC induction motor o (D) DC series wound electric motor If choice A is selected set score to Which of the following designs is the most satisfactory method for attaching turbine blades to the rotor disk? o (A) Pinning design. o (B) Locking tab design. (C) Fir-tree design. o (D) Retaining ring design. 54. Wrenches that are recommended for use on gas turbine engines should be plated with which of the following elements? o (A) Bronze (B) Nickel o (C) Carbon o (D) Silver Page 12 of 23

13 55. An axial compressor stator vane that is mechanically adjusted to provide optimum compressor performance over a wide operating range is referred to as which of the following? o (A) Variable Guide Vane (VGV) o (B) Static Guide Vane (SGV) (C) Variable Stator Vane (VSV) o (D) Inlet Guide Vane (IGV) 56. The only hand tools that should be used on gas turbine engines are chrome plated, nickel plated, or which of the following? o (A) Cadmium plated (B) Unplated o (C) Silver plated o (D) Bronze plated 57. To keep the exit pressures relatively constant across a HP turbine blade, which type of construction is generally utilized? o (A) Curtis. (B) Impulse-Reaction. o (C) Impulse. o (D) Rateau. 58. Which of the following conditions permits a gas turbine to produce 100% power? o (A) Maximum fuel flow. (B) Minimum air inlet temperature. o (C) Maximum combustion temperature. o (D) Minimum air mass/weight flow. 59. A centrifugal flow gas turbine uses what type of combustion chamber? o (A) double-annular (B) can o (C) can-annular o (D) annular Page 13 of 23

14 60. Under standard atmospheric conditions, PSIG converts to approximately what in absolute pressure? o (A) PSIA o (B) PSIA o (C) PSIA (D) PSIA 61. 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) Precipitator o (C) Reciprocator (D) Dehumidifier 62. The lube oil system shown in the illustration, consists of which of the following sub-systems? Illustration GT-0024 o (A) Lube oil scavenging. o (B) Sump venting. o (C) Lube oil supply. (D) All of the above. 63. 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 64. The turbine nozzle blades convert the combustion gases heat and pressure energy into what form of energy? o (A) Electrical o (B) Chemical o (C) Thermal (D) Velocity Page 14 of 23

15 65. What is the disadvantage of a dual-entry centrifugal compressor compared to a single-entry centrifugal compressor? o (A) The dual-entry compressor has a greater efficiency. o (B) The dual-entry compressor rotates at slower speeds. o (C) The dual-entry compressor is larger in diameter. (D) The dual-entry compressor utilizes a more complicated inlet ducting. 66. What is the term given to a process that occurs without a loss or gain of heat? o (A) Exothermic. o (B) Isothermal o (C) Endothermic. (D) Adiabatic 67. 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) Right side of the compressor to the left side. o (B) Left side of the power turbine to the right side. o (C) Intake end, looking toward the exhaust end. (D) Rear (exhaust end), looking toward the intake end. 68. In a gas turbine engine, the majority of the energy is added to the working fluid in which of the following components? (A) Combustor. o (B) Power turbine. o (C) Compressor. o (D) High-pressure turbine. If choice A is selected set score to Compared to other types of engines, what is the biggest advantage of a gas turbine engine? o (A) Simplicity of the control circuits. (B) Highest power-to-weight ratio. o (C) Low power-to-weight ratio. o (D) Simplicity of installation. Page 15 of 23

16 70. The two main types of compressor stall are known as what? o (A) Flame out and inlet temperature stall. o (B) Overspeed and overload stall. (C) Steady state and transient. o (D) Rapid rise and temperature inversion. Page 16 of 23

17 National Maritime Center Providing Credentials to Mariners GT /10/2015 Adapted for testing purposes only from Gas Turbine Systems Supervisor NAVEDTRA Further reproduction prohibited without permission. Page 17 of 23

18 National Maritime Center Providing Credentials to Mariners GT-0017 EE DD FF CC BB AA Adapted for testing purposes only from Gas Turbine Systems Technician (Electrical) 3/ Gas Turbine Systems Technician (Mechanical) 3, Volume 2 NAVEDTRA /26/2015 Further reproduction prohibited without permission. Page 18 of 23

19 National Maritime Center Providing Credentials to Mariners GT-0018 Adapted for testing purposes only from Gas Turbine Systems Technician (Electrical) 3/ Gas Turbine Systems Technician (Mechanical) 3, Volume 1 NAVEDTRA /29/2015 Further reproduction prohibited without permission. Page 19 of 23

20 National Maritime Center Providing Credentials to Mariners GT /1/2015 Adapted for testing purposes only from Gas Turbine Systems Technician (Electrical) 3/ Gas Turbine Systems Technician (Mechanical) 3, Volume 2 NAVEDTRA Further reproduction prohibited without permission. Page 20 of 23

21 National Maritime Center Providing Credentials to Mariners GT /13/2015 Adapted for testing purposes only from Hunt, Modern Marine Engineer's Manual, Volume I, 3rd edition. Copyright 1999 by The Cornell Maritime Press. Further reproduction prohibited without permission. Page 21 of 23

22 National Maritime Center Providing Credentials to Mariners GT /14/2015 Adapted for testing purposes only from Gas Turbine Systems Technician (Electrical) 3/ Gas Turbine Systems Technician (Mechanical) 3, Volume 2 NAVEDTRA Further reproduction prohibited without permission. Page 22 of 23

23 National Maritime Center Providing Credentials to Mariners GT /21/2015 Adapted for testing purposes only from Gas Turbine Systems Supervisor NAVEDTRA Further reproduction prohibited without permission. Page 23 of 23