Marine Diesel Engine Scavenge Fire

A fire which occurs in scavenge space or under piston space is called scavenge fire.

For a scavenge fire to begin there must be a combustible material,oxygen and heat source. In case of scavenge fire combustible material is oil. Oil can be cylinder oil drained down or crankcase oil carried upwards due to a faulty stuffing box. In some cases fuel oil can also be present due to poorly maintained combustion gear.Oxygen for combustion comes from scavenge air which is plentiful.Source of ignition could be piston blow by, after burning,late ignition etc.

Indications of scavenge fire:

• increase in exhaust temperature of affected unit as unit is starving from fresh air
• drop in rpm
• black smoke in exhaust
• discharge of black smoke,flame,spark through scavenge air box drain
• turbocharger surging
• local heating of scavenge air receiver
• jacket temp of affected unit rises

Causes of Scavenge fire:

• accumulation of cylinder oil due to excess lubrication
• unburnt fuel due to - leaky piston rings,prolonged blow by, worn liners, after burning
• accumulation of sludge

Actions to be taken:

• call all engineers alarm- inform wheel house- reduce engine rpm
• fuel pump of affected unit to be cut off
• rate of lubrication of affected unit to be increased

if fire is not subsiding

• stop engine
• stop aux blowers
• inject smothering gas [steam or co2]
• cooling system to be maintained
• after engine is cooled down, clean scavenge air receiver, cause of fire should be ascertained and rectified.

Probable places where damage might occur:

• stuffing box
• piston rod
• cylinder liner surface
• Tie rods near fire to be retensioned

Preventive maintenance:

• periodic inspection of scavenge air receiver
• scavenge drains should be blown regularly
• piston rings and liner to be properly maintained
• correct rate of cylinder lubrication to be maintained
• proper maintenance of fuel gear
• cylinder liner wear rate is to be checked and tracked on

*Well maintained scavenge space

Safety devices:

• scavenge air temperature sensors
• pressure relief valves
• fire extinguishing medium[co2 or steam]