Question: What Do You Mean By Scavenge Fire And How Does It Take Place?
Answer: Scavenge Fire Is A Condition In Which Ignition Of Scrapped Cylinder L.o. Takes Place In The Under Piston Space Resulting In Fire. To Complete A Fire Triangle Three Elements Are Required:
1. Combustible Substance/ Hydrocarbon.
2. Heat Source.
3. Air (quantity Of Oxygen More Than 8%).
Here, These Three Are In Form Of Scrapped Cylinder Lub Oil, Scavenge Air And A Heat Source May Be Due To Blow Past Of Combustion Gases. These Elements Combine In The Under Piston Space Under Specific Conditions To Cause Scavenge Fire.
Question: What Are The Probable Cause Of Scavenge Fire?
Answer: As Air Is Continuously Supplied In The Scavenge Space Whenever The Engine Is Running, So Scavenge Fire Can Take Place Due To Improper Combustion And Prolonged Blow Past Which Results In Accumulation Of Carbonaceous Matters In The Under Piston Space. Any Excess Cylinder Oil May Also Be Scraped Down By Piston Rings And Deposit In This Space. If The Situation Is Allowed To Continue, Burning Carbon Particles In The Blow Past Gases May Heat Up And Eventually Set The Deposits On Fire. Ignition May Also Be Caused By Slow Combustion Of Carbonaceous Matter Or By Blowback Of Hot Combustion Gases Through The Scavenge Air Ports Owing To Wrong Adjustment Of Exhaust Valve Or Excessive Back Pressure In The System.
Question: What Are The Indications/ Warnings Of A Scavenge Fire?
Answer: Indications Of Scavenge Fire:
1. Scavenge Space Fire Alarm (usually Set At 90 Deg C).
2. Loss In Power And Irregular Running Of The Engine.
3. Turbocharger Surging.
3. Increased Exhaust Temperature Of Effected Units.
4. Smoke From Turbocharger Air Filter.
5. Sparks From Scavenge Drains.
6. Scavenge Air Box Noticeably Hotter, Smoking Near The Seat Of Fire.
7. Peeling Of Paint From Under Piston Space.
8. Under Piston Temperature High
Question: What Are The Steps Taken In Case Of A Minor Scavenge Fire?
Answer: Minor Scavenge Fire Can Be Characterized By Localized Fire In One Unit Under Piston Space. Necessary Steps To Be Taken Are:
1. Continue To Run At Reduced Speed.
2. Cut Off The Fuel To Affected Unit.
3. Increase Cylinder L.o. Feed To Prevent Seizure.
4. All Scavenge Drains Must Be Shut To Prevent The Discharge Of Sparks And Burning Oil From The Drains Into The Engine Room.
5. Keep Clear Of Scavenge Doors And Crankcase Doors.
6. Keep Close Observation, Fire Should Die Out In 15-30 Mins.
7.When Temperatures Normal And No More Signs Of Scavenge Fire, Restore Fuel To Affected Unit, The Affected Units Should Be Run On Reduced Power (until Inspection Of The Scavenge Air Box And Overhaul Of The Cylinder And Piston Can Be Carried Out)
8. Reduce Cylinder L.o. Gradually To Normal.
Question: What Are The Steps Taken In Case Of A Major Scavenge Fire?
Answer:
1. Reduce Speed, Stop Engine As Soon As Possible.
2. Auxiliary Blowers Off.
3. Shut Off Fuel Oil Supply.
4. Shut Off L.o. Supply.
5. Cover Turbocharger Blower Filter.
6. Introduce Carbon Dioxide Or Other Fire Fightingmedium .
7. Apply External Cooling If Necessary.
8. Wait Till Fire Is Extinguished And Temperature Falls Below 80 Deg C.
9. Open Scavenge Doors, Ventilate, Cool.
10. When Safe, Enter Space , Thoroughly Clean Examine For Any Damages, Repair As Necessary.
11. Try To Ascertain The Causes And Remove The Cause If Possible.
12. Restart The Engine After Necessary Preparation, Raise Fuel Slowly And Step By Step Keeping Close Observation, Revert To Normal Running Conditions If All Found In Order.
Question: What Are The Measures Should Be Taken To Prevent Scavenge Fire?
Answer:
1.To Prevent Scavenge Fires Good Maintenance And Correct Adjustment Must Be Carried Out. Scavenge Space Must Be Periodically Inspected And Cleaned To Prevent Sludge Deposition. The Drain Should Be Cleared. Scavenge Drains Should Be Blown Regularly And Any Passage Of Oil From Them Noted. The Piston Rings Clearances Must Be Properly Maintained And Should Be Checked For Adequate Lubrication To Prevent Blow-by.
2.The Piston-rod Packing Rings And Scraper Rings Should Also Be Regularly Adjusted So That Oil Is Prevented From Entering The Scavenge Space.
3.Fuel Injection Equipment Must Be Kept In Good Condition, Timed Correctly.
4.If Cylinder Liner Has Completed Its Running Hours, It Should Be Calibrated And Should Be Renewed If Liner Wear Is Not In Limits.