AME - Aircraft Maintenance Engineer Gas Turbine Engine Theory Questions and Answers — Questions and Answers
Question 1: Which of the following describes the primary function of the turbine section in a gas turbine engine?
- To increase the pressure of the air entering the combustion chamber.
- To mix fuel with compressed air and ignite the mixture.
- To drive the compressor and accessories by extracting energy from the hot gas stream. (Correct answer)
- To decrease the velocity of the exhaust gases to prevent structural damage.
Correct answer: To drive the compressor and accessories by extracting energy from the hot gas stream.
The turbine section's main purpose is to extract kinetic and thermal energy from the high-velocity hot gases exiting the combustion chamber. This extracted energy is converted into mechanical power to rotate the main shaft, which in turn drives the compressor section and engine-driven accessories.
Question 2: A turbofan engine is operating at a constant high-altitude cruise. If the density of the air entering the engine decreases, what is the most likely effect on engine performance, assuming RPM remains constant?
- Thrust will increase due to lower air resistance.
- Thrust will decrease due to reduced mass airflow. (Correct answer)
- Fuel consumption will decrease significantly.
- Exhaust gas temperature (EGT) will decrease.
Correct answer: Thrust will decrease due to reduced mass airflow.
Thrust is a product of mass airflow and the change in velocity. At a constant RPM, the compressor moves a constant volume of air. If the air density decreases, the mass of that air (mass airflow) also decreases. This reduction in mass airflow directly leads to a decrease in the thrust produced by the engine.
Question 3: In the context of the Brayton cycle as it applies to a gas turbine engine, what process occurs within the combustion chamber?
- Isentropic compression
- Constant-pressure heat addition (Correct answer)
- Isentropic expansion
- Constant-volume heat addition
Correct answer: Constant-pressure heat addition
The Brayton cycle is the thermodynamic model for gas turbine engines. The process within the combustor, where fuel is burned to heat the compressed air, is modeled as a constant-pressure (isobaric) heat addition process.
Question 4: An aircraft's turboprop engine utilizes its gas turbine core primarily to do what?
- Generate the majority of its thrust from the high-velocity exhaust gases.
- Drive a large fan for high-bypass airflow.
- Drive a propeller through a reduction gearbox. (Correct answer)
- Heat the air for a ramjet effect at high speeds.
Correct answer: Drive a propeller through a reduction gearbox.
In a turboprop engine, the vast majority of the energy produced by the gas turbine section is used to drive a propeller via a reduction gearbox. The propeller then accelerates a large mass of air, generating most of the engine's thrust. A small amount of thrust is produced by the exhaust gases.
Question 5: During engine operation, the airflow passages in the compressor section are designed to be divergent in shape between stages. What is the primary purpose of this design?
- To increase the velocity of the airflow for better combustion.
- To decrease the pressure of the airflow while increasing its velocity.
- To convert the kinetic energy (velocity) of the airflow into potential energy (pressure). (Correct answer)
- To cool the compressed air before it enters the combustor.
Correct answer: To convert the kinetic energy (velocity) of the airflow into potential energy (pressure).
In a compressor, the stator vanes form divergent passages after the rotating blades. These passages are designed to slow down the airflow, converting its kinetic energy (velocity) into a rise in static pressure. This process increases the pressure of the air layer by layer through the compressor stages.
Question 6: A maintenance technician is inspecting the combustion section of a gas turbine engine. Which of the following is a primary function of this section?
- To extract mechanical energy to power the engine's accessories.
- To add chemical energy to the compressed air by burning fuel at a constant pressure. (Correct answer)
- To increase the mass of air flowing through the engine using bypass ducts.
- To reduce the temperature of the gas stream before it enters the turbine.
Correct answer: To add chemical energy to the compressed air by burning fuel at a constant pressure.
The combustion chamber's primary role is to add energy to the system. It does this by mixing fuel with the high-pressure air from the compressor and burning the mixture. This combustion process occurs at a relatively constant pressure and dramatically increases the temperature and volume of the gases before they enter the turbine.
AME - Aircraft Maintenance Engineer Gas Turbine Engine Theory Questions and Answers
Which of the following describes the primary function of the turbine section in a gas turbine engine?