WHAT IS SCAVENGE FIRE, REASON AND INDICATION OF SCAVENGE FIRE

SCAVENGE FIRE

• FOR SCAVENGE FIRE TO TAKE PLACE WE NEED ALL THREE ELEMENT OF FIRE TRIANGLE AIR(OXYGEN) COMBUSTIBLE MATERIAL AND HEAT SOURCE OR TEMP HIGH ENOUGH TO INITIATE COMBUSTION.
• THE COMBUSTIBLE MATERIAL CAN BE CYLINDER OIL WHICH IS DRAINED FROM THE CYLINDER SPACES.
• THE COMBUSTIBLE MATERIAL CAN ALSO BE CRANK CASE OIL WHICH IS CARRIED UPWARD BY PISTON ROD DUE TO FAULTY STUFFING BOX.
• IN CERTAIN CASES CYLINDER OIL RESIDUES CAN ALSO BE MIXED WITH FUEL OIL WHICH MAY BE DUE TO FAULTY INJECTOR,INJECTOR WITH INCORRECT PRESSURE SETTING,FUEL PARTICLE STRIKING IN CYLINDER AND OTHER SUCH REASON.
• THE OXYGEN COMES FROM SCAVENGE AIR WHICH IS REQUIRED FOR FUNCTIONING OF ENGINE.
• THE HEAT SOURCE CAN BE ENGINE BLOW PAST OR SLOW IGNITION OR AFTER BURNING OR EXCESSIVE EXHAUST BACK PRESSURE.
• THIS WILL RESULT IN BLOW BACK FROM SCAVENGE PORTS.

REASON FOR SCAVENGE FIRE 

• BLOW PAST OF COMBUSTION PRODUCT WHICH COULD BE CAUSED DUE TO LEAKY, STICKY OR BROKEN PISTON RING, WORN OUT LINER, FAULTY CYLINDER LUBRICATION, INSUFFICIENT AXIAL CLEARANCE OF PISTON RINGS.
• OVER HEATED PISTON DISSIPATES HEAT TO THE UNDER PISTON HEAT TO UNDER PISTON AREA CAUSED BY FAULTY ATOMISATION AND INJECTION PRESSURE, FAULTY FUEL PUMP TIMING, LOSS OF COMPRESSION, ENGINE OVERLOAD, FAILURE OF COOLANT CIRCULATION OF INSUFFICIENT COOLING DUE TO FORMATION OF SCALE.
• BLOW BACK OF EXHAUST GASES CAUSED BY EXHAUST BACK PRESSURE OR DEPOSIT ON EXHAUST PORT, FOULING OF GRID BEFORE TURBINE INLET, FOULING OF TURBINE BLADES, CHOCKING OF EGB OR ECONOMISER GAS OUTLET.
• PRESENCE OF FUEL OIL IN THE SCAVENGE SPACES DUE TO DEFECTIVE FUEL INJECTORS OR FUEL PARTICLES LANDING ON THE CYLINDER LINER DUE TO EXCESSIVE PENETRATION.
• EXCESSIVE CYLINDER LUBRICATION WHICH IS DRAINED DOWN TO SCAVENGE SPACES.

INDICATION OF SCAVENGE FIRE

ONE SHOULD BE EXTREMELY CAUTIOUS IN CASE ANY OF THE BELOW MENTIONED CONDITION IS OBSERVED.

• SCAVENGE TEMPERATURE WILL START INCREASING.
• THE TURBOCHARGER WILL START SURGING.
• HIGH EXHAUST TEMPERATURE.
• LOSS OF ENGINE POWER AND REDUCTION IN RPM. THIS HAPPENS BECAUSE OF BACKPRESSURE IS CREATED UNDER PISTON SPACE DUE TO FIRE.
• SMOKE COMING OF THE SCAVENGE DRAINS.
• THE PAINT BLISTER WILL BE FORMED ON THE SCAVENGE DOORS DUE TO HIGH TEMPERATURE BUT THIS WILL OCCUR ONLY IN LARGE FIRES AND EXTREME CASES.

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