Scavenge Space

Question 1

1. With reference to large slow speed diesel engines,

a) State four possible factors leading to a scavenge fire.

Answer 1

a) Poor Maintenance
Badly worn or failed piston rings
Blocked stuffing box drain
Over injection of fuel oil

Question 2

1. With reference to large slow speed diesel engines,
   a) State four possible factors leading to a scavenge fire.
   b) State four indications of a scavenge fire.

Answer 2

b) High scavenge temperature in one or more units
Turbocharger surging
Increased scavenge pressure
Paint discolouration

Question 3

2. a) State FOUR important factors which contribute to the initiation of a scavenge fire.

Answer 3

a) Damaged or worn piston rings
Leaking fuel injector
Over lubrication of cylinder
Lack of regular maintenance and scavenge space cleaning

Question 4

2. a) State FOUR important factors which contribute to the initiation of a scavenge fire. b) State the duties of the Engineer Officer of the Watch on discovering a scavenge fire.

Answer 4

b) Inform the bridge and chief engineer and request the engine to be slowed down Isolate the fuel supply to the effect unit
Open the indicator cock
Administer steam or other fixed installed fire suppression system

Question 5

3. a) Describe the actions to be taken by the Engineer Officer of the Watch on discovering a scavenge fire.

Answer 5

a) Inform the bridge and chief engineer and request the engine to be slowed down Isolate the fuel supply to the effect unit
Open the indicator cock
Administer steam or other fixed installed fire suppression system

Question 6

3. a) Describe the actions to be taken by the Engineer Officer of the Watch on discovering a scavenge fire.
   b) State two dangers of allowing a scavenge fire to exist.

Answer 6

b) A loss of power to one unit on the engine will cause irregular running. The remaining units will take more load, which cause damage or misalignment to engine components such as the piston and piston rod.
Excessive temperatures will put the engine components under stress, if the diaphragm plate cracks and hot gases are allowed into the crankcase, it could cause a crankcase explosion.

Question 7

4. State four actions to be taken by the EOOW on discovering:
   a) A scavenge fire in one engine unit only;
   b) A scavenge fire in several engine units at the same time.

Answer 7

a) Raise the alarm 
Request to reduce engine speed 
Shut off fuel to affected cylinder 
Increase cylinder lubrication and monitor, if the fire increases then reduce. Allow the fire  to burn itself out. 
b) Raise the alarm 
Request to stop the engine 
Engage turning gear 
If fitter, smother with firefighting system, if not boundary cool in small doses to stop the  bilges from filling.

Question 8

5. a) Explain the procedure to be carried out before the inspection of the scavenge space on a large 2-stroke diesel engine.

Answer 8

a) The scavenge space is in considered an enclosed space, so the relevant permit to work must be filled out and signed. The engine must be tagged out properly the starting air must be locked off and the turning gear engaged. Signs must be posted to make others aware of the work being
undertaken. The space must be opened 24 hours in advance and ventilated. The atmosphere must be tested immediately prior to entry, and a tester should be carried by the person(s) entering. Any hinged doors must be secured open to prevent accidental closure. Enclosed space procedures apply with regards to a safety number being posted outside and emergency equipment must be at hand.

Question 9

5. a) Explain the procedure to be carried out before the inspection of the scavenge space on a large 2-stroke diesel engine.
   b) State four reasons for carrying out a scavenge space inspection.

Answer 9

b) To check the cleanliness of the space
To check the condition of the piston rings
To check the condition of the cylinder liner
To check that the scavenge drains are clear of blockage

Question 10

6. With reference to the operation of main propulsion engine, outline the importance of each of following:
   a) Maintaining the temperature of the scavenge air above the dewpoint;
   b) Maintaining the fuel at the correct viscosity for injection;
   c) Regular on board testing of the lubricating oil;
   d) Ensuring rotation of the exhaust valves.

Answer 10

a) To prevent cold corrosion due to the formation of condensate which when mixed with acidic combustion products forms an acidic solution such as sulphuric acid.
b) To prevent over pressurisation of fuel rail components and to maintain proper injection of fuel.
c) To indicate any potential contaminants such as water or metal that would cause damage, to monitor the degradation of the oil.
d) To ensure even carbon deposit build-ups, cleaning and maintaining the valve seat.