Scavenge Space Page 25-27

Question 1

State four possible factors leading to a scavenge fire.

Answer 1

1. Blocked scavenge drains
2. Broken piston rings
3. Excessive cylinder lubrication oil
4. Excessive wear of the liner and excess lubrication drained down from cylinder space

Question 2

State four indications of a scavenge fire.

Answer 2

1. High scavenge temperature
2. High exhaust temperature in affected unit
3. Smoke from scavenge drains
4. Black smoke or sparks from funnel

Question 3

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

Answer 3

1. Authorised by company, C/E and port authority
2. Permit to work & Risk assessment
3. Ensure turning gear is engaged so moving parts are free to move (Clear any gases)
4. Keep indicator cocks open to expel any combustion gases or water or oil in system
5. Ensure turning gear remote is with you at all times
6. Open scavenge drains
7. Carry out enclosed entry procedure after gaining permission

Question 4

State FOUR reasons for carrying out a scavenge space inspection.

Answer 4

1. Assessing wear of liner, piston and piston rings
2. Assessing the condition of auxiliary blower flaps & turbocharger flaps
3. Assessing any damage after a scavenge space fire
4. Removal of carbon, oil and other deposits that may lead to a scavenge space fire or scavenge port blockage

Question 5

State four important factors which contribute to the initiation of a scavenge fire.

Answer 5

1. Combustible material such as FO from leaking fuel injector or improper timing causing poor combustion & over injection of fuel oil.
2. Damaged or worn piston rings causing blow by of high temperatures could ignite carbon deposits.
3. Over lubrication of cylinder.
4. Lack of regular maintenance and scavenge space cleaning causing build-up of carbon deposits.

Question 6

State the duties of the engineer officer of the watch on discovering a scavenge fire.

Answer 6

1. Inform the bridge and chief engineer to make them aware of the M.E condition
2. Request permission that the engine be slowed down to limit fuel oil and combustion air
3. Isolate the fuel supply to the affected unit or all of main engine
4. Maintain lubrication and water cooling to the affected unit(s)
5. Close scavenge drains to prevent sparks & burning oil entering engine room
6. Prepare an auxiliary generator to maintain power supply if main engine is shut down
7. Shut off auxiliary blowers
8. Start auxiliary boiler if not automatic
9. If small fire, it may blow out by itself; if not, administer steam smothering or other fixed installed fire suppression system

Question 7

What is the importance of maintaining the temperature of the scavenge air above the dew point?

Answer 7

To prevent condensate water formation, which when mixed with exhaust products such as sulphur creates acidic products; this will cause acidic cold corrosion damaging scavenge components, cylinders and even pistons.

Question 8

What are two dangers of allowing a scavenge fire to exist?

Answer 8

1. Severe damage to piston, liner and piston rings due to excessive heat.
2. Spread of fire to other units, potential for a crank case explosion.

Question 9

What actions should be taken by the Engineer Officer of the Watch on discovering a scavenge fire in one engine unit only?

Answer 9

1. Inform the bridge and chief engineer. Request the engine to be slowed.
2. Remove fuel from the affected unit.
3. Increase cylinder lubrication.
4. Monitor the temperature including neighbouring units; if still increasing, administer steam.

Question 10

What actions should be taken by the Engineer Officer of the Watch on discovering a scavenge fire in several units at the same time?

Answer 10

1. Inform the bridge and chief engineer. Request the engine to be slowed or stopped.
2. If within engine specification, remove fuel from affected units; if not, stop the engine.
3. Administer steam, use the turning gear to turn the engine whilst maintaining lubrication.
4. Set up boundary cooling on scavenge space if severe; after extinguishing, carry out a full inspection.

Question 11

What is the importance of maintaining the fuel at the correct viscosity for injection?

Answer 11

To prevent over pressurisation of fuel rail components and to maintain proper injection of fuel to achieve efficient combustion of the fuel oil and to reduce fuel consumption and exhaust space fouling.

Question 12

What is the importance of regular on board testing of the lubricating oil?

Answer 12

To indicate any potential contaminants such as water or metal that would cause damage, to monitor the degradation of the oil.

Question 13

What is the importance of ensuring rotation of the exhaust valves?

Answer 13

To ensure even carbon deposit build-ups, cleaning and maintaining the valve seat.

Question 14

tion
With reference to the operation of main propulsion engines, outline the importance of each of the following:
a. Maintaining the temperature of the scavenge air above the dew point (2)
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. Maintaining the fuel at the correct viscosity for injection (2)
To prevent over pr

Answer 14

With reference to the operation of main propulsion engines, outline the importance of each of the following:
a. Maintaining the temperature of the scavenge air above the dew point (2)
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