AMT Turbine Engine Principles Questions and Answers — Questions and Answers
Question 1: The operation of a gas turbine engine is described by the Brayton cycle. Which of the following represents the correct sequence of the four events in an ideal Brayton cycle?
- Intake, Compression, Combustion, Exhaust
- Compression, Power, Intake, Exhaust
- Intake, Power, Combustion, Compression
- Compression, Combustion, Expansion, Exhaust (Correct answer)
Correct answer: Compression, Combustion, Expansion, Exhaust
The ideal Brayton cycle 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). This is best summarized as Compression, Combustion, Expansion, and Exhaust.
Question 2: In a gas turbine engine, what is the primary function of the diffuser section located between the compressor and the combustion chamber?
- To increase the velocity and decrease the pressure of the air.
- To decrease the velocity and increase the pressure of the air. (Correct answer)
- To mix the compressed air with fuel before combustion.
- To add swirl to the airflow for better combustion stability.
Correct answer: To decrease the velocity and increase the pressure of the air.
The diffuser is a duct with an expanding internal diameter. Its purpose is to slow down the high-velocity air leaving the compressor, converting its kinetic energy into potential energy in the form of increased static pressure. This high-pressure, low-velocity air is ideal for efficient combustion.
Question 3: Which of the following is a primary advantage of an axial-flow compressor compared to a centrifugal-flow compressor in large, high-performance turbine engines?
- Simpler and more rugged construction.
- Higher pressure rise per stage.
- Greater efficiency and ability to handle high mass airflow. (Correct answer)
- Wider range of stable operational speeds.
Correct answer: Greater efficiency and ability to handle high mass airflow.
Axial-flow compressors are capable of handling a very large mass of air for a given frontal area and can achieve very high overall compression ratios with high efficiency through multiple stages. This makes them ideal for large engines where high thrust and fuel efficiency are required. Centrifugal compressors typically have a higher pressure rise per stage but are limited in overall mass airflow and are less efficient in very large applications.
Question 4: A modern commercial airliner is typically powered by high-bypass turbofan engines. What is the main benefit of having a high bypass ratio?
- Higher exhaust gas temperature for increased thrust.
- Increased core engine speed for faster acceleration.
- Improved fuel efficiency and reduced engine noise. (Correct answer)
- Simplified engine design with fewer moving parts.
Correct answer: Improved fuel efficiency and reduced engine noise.
In a high-bypass engine, a large volume of air is accelerated by the fan and bypasses the engine core. This large mass of slower-moving air produces the majority of the thrust more efficiently than a smaller mass of high-velocity gas from the core. This results in significantly better thrust-specific fuel consumption (fuel efficiency) and lower noise levels.
Question 5: While a gas turbine engine's ultimate purpose is to produce thrust, what is the primary role of the turbine section within the engine?
- To ignite the fuel-air mixture.
- To create the final high-velocity exhaust stream.
- To extract energy from the hot gases to drive the compressor and accessories. (Correct answer)
- To reduce the pressure of the exhaust gases to ambient levels.
Correct answer: To extract energy from the hot gases to drive the compressor and accessories.
The primary function of the turbine section is to extract kinetic and thermal energy from the high-velocity gases leaving the combustion chamber. This extracted energy is converted into mechanical work to rotate the main shaft, which in turn drives the compressor section and engine-driven accessories like fuel pumps and generators.
Question 6: The production of thrust in a turbine engine is best explained by which physical principle?
- Bernoulli's Principle
- Pascal's Law
- Newton's Third Law of Motion (Correct answer)
- The Venturi Effect
Correct answer: Newton's Third Law of Motion
Newton's Third Law states that for every action, there is an equal and opposite reaction. A turbine engine produces thrust by taking in a mass of air and accelerating it out the back at a high velocity (the action). The engine and the aircraft are then pushed forward by an equal and opposite force (the reaction).
AMT Turbine Engine Principles Questions and Answers
The operation of a gas turbine engine is described by the Brayton cycle.
Which of the following represents the correct sequence of the four events in an ideal Brayton cycle?