AMT Powerplant Theory and Maintenance 3 — Questions and Answers
Question 1: Which statement about pre-ignition in a reciprocating engine is correct?
- Pre-ignition occurs after normal spark plug firing and increases power
- Pre-ignition occurs before the spark plug fires and can cause engine damage (Correct answer)
- Pre-ignition is caused by a retarded ignition timing setting
- Pre-ignition is harmless and self-correcting
Correct answer: Pre-ignition occurs before the spark plug fires and can cause engine damage
Pre-ignition occurs when the fuel-air charge ignites before the spark plug fires, often due to a hot spot, and can cause severe engine damage.
Question 2: The compressor pressure ratio of a turbine engine is defined as:
- Turbine inlet pressure divided by exhaust pressure
- Compressor outlet total pressure divided by compressor inlet total pressure (Correct answer)
- Mass airflow at the inlet divided by mass airflow at the outlet
- Fuel flow rate divided by airflow rate
Correct answer: Compressor outlet total pressure divided by compressor inlet total pressure
Compressor pressure ratio is the ratio of total air pressure at the compressor outlet to total air pressure at the compressor inlet, indicating compression efficiency.
Question 3: A reciprocating engine has excessive blow-by past the piston rings. Which instrument indication would you expect?
- High oil temperature with normal oil pressure
- Low cylinder head temperature
- Increased oil consumption and crankcase pressure (Correct answer)
- Lower-than-normal manifold pressure
Correct answer: Increased oil consumption and crankcase pressure
Blow-by allows combustion gases to pass the piston rings into the crankcase, causing increased crankcase pressure and oil consumption.
Question 4: During turbine engine ground run-up, a 'hung start' is characterized by:
- Engine RPM exceeding limits during start
- RPM stabilizing below idle with exhaust temperature continuing to rise (Correct answer)
- Oil pressure failing to rise within the specified time
- Compressor stall immediately upon introduction of fuel
Correct answer: RPM stabilizing below idle with exhaust temperature continuing to rise
A hung start occurs when the engine lights off but RPM stabilizes at a sub-idle value while EGT continues to rise, risking a hot start.
Question 5: What does the term 'specific fuel consumption' (SFC) describe in turbine engines?
- The maximum fuel load the engine can process per hour
- The pounds of fuel burned per hour per pound of thrust produced (Correct answer)
- The ratio of fuel flow to compressor airflow
- The fuel efficiency relative to ambient temperature
Correct answer: The pounds of fuel burned per hour per pound of thrust produced
Specific fuel consumption (SFC) is the ratio of fuel flow (lb/hr) to thrust produced (lb), measuring how efficiently an engine converts fuel into thrust.
Question 6: Which ignition system component stores energy and releases it as a high-intensity spark during engine starting in a gas turbine?
- Magneto
- Capacitor-discharge exciter box (Correct answer)
- Spark plug resistor
- Distributor rotor
Correct answer: Capacitor-discharge exciter box
The capacitor-discharge exciter box stores electrical energy and releases it as a high-voltage, high-energy spark to the igniters during turbine engine starting.
Question 7: Which of the following best describes 'compressor stall' in a gas turbine engine?
- The compressor rotor exceeds its design RPM limit
- Airflow through a compressor stage separates from the blade surfaces, causing flow disruption (Correct answer)
- The compressor inlet guide vanes close completely
- Fuel flow exceeds the compressor's capacity to atomize it
Correct answer: Airflow through a compressor stage separates from the blade surfaces, causing flow disruption
Compressor stall occurs when the angle of attack on compressor blades becomes excessive, causing boundary layer separation and disrupted airflow.
AMT Powerplant Theory and Maintenance 3
Which statement about pre-ignition in a reciprocating engine is correct?