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Causes and Prevention of Scavenge Fire

Scavenge fire occurs when carbonized lube oil, unburnt fuel oil, and carbon accumulate in the scavenge spaces of an engine and ignite under faulty running conditions. Causes include blow past of combustion products, overheated pistons, blow back of exhaust gases, presence of fuel oil in scavenge spaces, and excessive cylinder lubrication. Indications are reduced engine revolutions, unstable turbocharger operation, increased exhaust temperature of affected cylinders, black smoke, smoke from scavenge drains, and visible fire. Actions to take include reducing speed, cutting fuel to affected unit, increasing cylinder lubrication, closing drains, and releasing smothering gases to extinguish the fire. Prevention methods

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191 views3 pages

Causes and Prevention of Scavenge Fire

Scavenge fire occurs when carbonized lube oil, unburnt fuel oil, and carbon accumulate in the scavenge spaces of an engine and ignite under faulty running conditions. Causes include blow past of combustion products, overheated pistons, blow back of exhaust gases, presence of fuel oil in scavenge spaces, and excessive cylinder lubrication. Indications are reduced engine revolutions, unstable turbocharger operation, increased exhaust temperature of affected cylinders, black smoke, smoke from scavenge drains, and visible fire. Actions to take include reducing speed, cutting fuel to affected unit, increasing cylinder lubrication, closing drains, and releasing smothering gases to extinguish the fire. Prevention methods

Uploaded by

Xahid Hasan
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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What is scavenge fire?

Carbonized lube oil, unburnt fuel oil and carbon from the residual products of the
combustion spaces are accumulated in the scavenge spaces with the running of the
engine. Under certain faulty running condition of the engine, these may ignite
causing a fire in the enclosed scavenge space, known as scavenge fire.

Causes of Scavenge Fire

1. Blow past of combustion products


(caused by leaky, sticky or broken piston rings, worn out liner, faulty cylinder
lubrication, or insufficient axial clearance of the piston rings.)

2. Overheated piston dissipates heat to the under piston area


(caused by faulty atomization and injection pressure, faulty fuel pump timing,
loss of compression, engine overload, failure of coolant circulation or
insufficient cooling due to formation of scale.)

3. Blow back of exhaust gases


(caused by exhaust back pressure or deposits on exhaust ports, fouling of grid
before turbine inlet, fouling of turbine blades, choking of EGB or economiser
gas outlet.)
4. Presence of fuel oil in the scavenge spaces
(due to defective fuel injectors, incorrect pressure setting of injectors or fuel
particles landing on the cylinder liner due to excessive penetration.)

5. Excessive cylinder lubrication which is drained down to scavenge spaces.

6. By overloading the Engine

Indication of Scavenge Fire

1. Engine revolution drops (as the power generation in the affected cylinder is
reduced).
2. Unstable operation of Turbo charger and may cause surging.
3. Exhaust temperature of the affected cylinder increases, (as the cylinder is not
receiving fresh air.)
4. Black smoke with exhaust (due to incomplete combustion in that unit.)
5. Discharging of spark, flame or smokes through drain cocks from scavenge
air boxes.
6. Visible evidence of fire if a transparent window is fitted.
7. Cooling water outlet temperature of the affected unit is increased.

Action to be taken

1. Inform bridge and reduce the speed.


2. Cut of fuel supply to the affected unit and shut off valves.
3. Cylinder lubrication is increased.
4. Drains to be shut to prevent flow of spark in engine room.
5. Keep clear of scavenge space relief valve to prevent human injury.

Fire should be extinguished after some time. If the fire spread in the other
scavenge spaces along with the scavenge manifold, then –

1. Inform bridge and stop the engine

2. Open indicator cocks, engage turning gear and turn engine to prevent engine
seizure
3. Normal engine cooling and lubrication are maintained

4. Release the smothering gases (Steam or CO2) to extinguish fire


5. Before opening scavenge door ventilate the space thoroughly if CO2 is
released.

Prevention of Scavenge Fire

1. Clean scavenge space and drain at regular intervals


2. Keep scavenge space drain open at regular intervals
3. Excess cylinder lubrication must be avoided
4. In case of timed lubrication, the time has to be checked as per PMS
5. Piston rings must be properly maintained and lubricated adequately
6. Piston rod stuffing box must be maintained to prevent oil ingress in the
scavenge space.
7. Prolong engine or any cylinder over loading to be avoided
8. Cylinder liner wear must be within admissible limits

Scavenge Space Protection Devices

1. Electrical temperature sensing device fitted within the trunking, which will
automatically sound an alarm in the event of excessive rise in local
temperature.

2. Pressure relief valves consisting of self closing spring loaded valves are
fitted and should be examined and tested periodically.

3. Fixed fire extinguishing system may be CO2, Dry Powder or Steam.

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