Free AMT Turbine Engine Principles Questions and Answers — Questions and Answers
Question 1: Which of the following describes the primary function of the diffuser section in a gas turbine engine?
- To increase the pressure and reduce the velocity of the air leaving the compressor. (Correct answer)
- To mix fuel and air and ignite the mixture.
- To expand the hot gases and drive the turbine wheel.
- To increase the velocity and decrease the pressure of the exhaust gases.
Correct answer: To increase the pressure and reduce the velocity of the air leaving the compressor.
The diffuser is a divergent duct located between the compressor section and the combustion section. Its purpose is to slow down the high-velocity air from the compressor and increase its pressure before it enters the combustion chambers, ensuring stable combustion.
Question 2: A turbofan engine has a bypass ratio of 5:1. What does this indicate?
- The fan is five times larger in diameter than the turbine.
- For every 1 part of air that goes through the engine core, 5 parts of air are bypassed around the core. (Correct answer)
- The engine produces five times more thrust than a comparable turbojet.
- Five parts of the exhaust gas are used for thrust, while one part is used for cooling.
Correct answer: For every 1 part of air that goes through the engine core, 5 parts of air are bypassed around the core.
Bypass ratio is a fundamental parameter of a turbofan engine. It is the ratio of the mass flow rate of the air that is bypassed around the engine core to the mass flow rate of the air that passes through the core. A 5:1 ratio means five times more air goes around the core than through it.
Question 3: During a routine inspection of a turbine engine, a technician finds minor pitting and small nicks on the leading edges of the first-stage compressor blades. According to typical maintenance standards, what is the most likely cause?
- Compressor stall
- Turbine blade failure
- Normal operational wear
- Foreign Object Damage (FOD) (Correct answer)
Correct answer: Foreign Object Damage (FOD)
Small nicks, dents, and pitting on the front-facing compressor blades are classic signs of Foreign Object Damage (FOD). This occurs when small, hard particles (like sand, ice, or runway debris) are ingested into the engine inlet and strike the rotating blades.
Question 4: What is the primary thermodynamic cycle upon which all gas turbine engines operate?
- The Otto cycle
- The Carnot cycle
- The Brayton cycle (Correct answer)
- The Rankine cycle
Correct answer: The Brayton cycle
The Brayton cycle is the thermodynamic model that describes the operation of a gas turbine engine. It consists of four processes: isentropic compression (in the compressor), constant-pressure heat addition (in the combustor), isentropic expansion (in the turbine), and constant-pressure heat rejection (exhaust).
Question 5: In a dual-spool, axial-flow compressor, how is the low-pressure compressor (N1) typically connected to its corresponding turbine?
- Through a reduction gearbox to the high-pressure turbine.
- It is mechanically independent and driven by bleed air.
- Via a concentric shaft that passes through the hollow high-pressure (N2) shaft. (Correct answer)
- Directly to the accessory gearbox.
Correct answer: Via a concentric shaft that passes through the hollow high-pressure (N2) shaft.
Dual-spool engines have two independent rotating assemblies. The low-pressure compressor (N1) is connected to the low-pressure turbine by a shaft that runs through the center of the hollow high-pressure (N2) shaft, which connects the high-pressure compressor and high-pressure turbine. This allows each spool to rotate at its own optimal speed.
Question 6: A technician is performing an engine trim on a turbine engine. The Exhaust Gas Temperature (EGT) is found to be exceeding the maximum limit at takeoff power, while other engine parameters like RPM and fuel flow are within their normal ranges. Which of the following is a plausible cause?
- A malfunctioning fuel control unit (FCU) delivering excessive fuel.
- Damage to the low-pressure compressor (N1) blades.
- A malfunctioning EGT indication system, such as a faulty thermocouple.
- An obstruction in the engine's exhaust nozzle. (Correct answer)
Correct answer: An obstruction in the engine's exhaust nozzle.
An obstruction or restriction in the exhaust nozzle would increase back pressure in the turbine section. This 'choking' effect would cause the hot gases to linger in the turbine section, leading to a rise in EGT without a corresponding increase in RPM or a command for higher fuel flow from the FCU.
Free AMT Turbine Engine Principles Questions and Answers
Which of the following describes the primary function of the diffuser section in a gas turbine engine?