STCW Marine Engineering 3 — Questions and Answers
Question 1: What is the purpose of an intercooler in a marine diesel engine air supply system?
- To heat the air to prevent condensation
- To cool compressed air from the turbocharger before it enters the engine (Correct answer)
- To filter salt from sea air
- To regulate exhaust back-pressure
Correct answer: To cool compressed air from the turbocharger before it enters the engine
Cooling the compressed air after the turbocharger (charge air cooling) increases air density, improving combustion efficiency and reducing thermal stress.
Question 2: In a marine refrigeration system, what is the role of the expansion valve?
- To increase refrigerant pressure before the condenser
- To reduce refrigerant pressure, causing it to vaporize and absorb heat (Correct answer)
- To separate oil from the refrigerant
- To superheat refrigerant vapor before the compressor
Correct answer: To reduce refrigerant pressure, causing it to vaporize and absorb heat
The expansion valve throttles high-pressure liquid refrigerant to low pressure, allowing it to evaporate and absorb heat from the space being cooled.
Question 3: What does 'cavitation' mean in the context of a centrifugal pump?
- Pump running at excessive speed
- Formation and collapse of vapor bubbles due to low inlet pressure, causing damage and loss of flow (Correct answer)
- Air leaking into the pump casing
- Bearing failure from insufficient lubrication
Correct answer: Formation and collapse of vapor bubbles due to low inlet pressure, causing damage and loss of flow
Cavitation occurs when local pressure drops below the liquid's vapor pressure, forming bubbles that collapse violently and erode pump components.
Question 4: Which STCW document outlines the minimum standards of competence for officers in charge of an engineering watch?
- STCW Code Section B-III/1
- MARPOL Annex VI
- ISM Code Chapter 9
- STCW Code Table A-III/1 (Correct answer)
Correct answer: STCW Code Table A-III/1
STCW Code Table A-III/1 specifies the minimum standard of competence for officers in charge of an engineering watch in a manned engine room.
Question 5: What is the purpose of the crankcase relief valve on a marine diesel engine?
- To maintain crankcase oil pressure
- To vent excessive crankcase pressure rapidly and prevent an explosion (Correct answer)
- To regulate oil temperature
- To allow inspection of crankcase bearings
Correct answer: To vent excessive crankcase pressure rapidly and prevent an explosion
Crankcase relief valves open rapidly during a crankcase explosion to release pressure, preventing catastrophic structural failure of the engine.
Question 6: What is the correct action when a crankcase explosion alarm activates on a running diesel engine?
- Immediately open the crankcase doors to inspect
- Reduce speed slowly and investigate the cause while running
- Shut down the engine, allow it to cool, then investigate (Correct answer)
- Increase ventilation and continue operation
Correct answer: Shut down the engine, allow it to cool, then investigate
Opening a hot crankcase immediately after an explosion risks introducing air to ignite hot oil mist; the engine must be stopped and allowed to cool before inspection.
Question 7: A diesel generator fails to start. After checking fuel supply and battery voltage are normal, what should be checked next?
- Turbocharger speed
- Starting air pressure or starting system solenoid valve (Correct answer)
- Exhaust temperature
- Jacket water temperature
Correct answer: Starting air pressure or starting system solenoid valve
Most marine diesel generators are air-started, so insufficient starting air pressure or a failed starting solenoid is the next most likely cause if fuel and power are confirmed good.
STCW Marine Engineering 3
What is the purpose of an intercooler in a marine diesel engine air supply system?