Crankcase Explosion

Question:What Do You Mean By Crankcase Explosion?
Answer: Crankcase Explosion Is An Accidental Explosion That Can Take Place In An Engine Crankcase. Onboard It Can Take Place In Main Engine And Auxiliary Engine Crankcase.

Q. What Are The Conditions That May Lead To Crankcase Explosion?
Ans: To Complete The Fire Triangle Air, Hydrocarbon And A Heat Source Is Required. An Engine Crankcase Is Continuously Under Positive Air Pressure, As It Is Open To Air Vent (breather Pipe), Hydrocarbon Is Accumulated By The Formation Of Oil Mist, And The Formation Of A Hotspot Acts A Heat Source. These Conditions Together Emanate Into Crankcase Fire.

Q. Explain The Complete Process Of Crankcase Fire?
Ans: Due To Continuous Lubrication, Oil Is Splashed On The Cylinder Liner Walls By The Churning Action Of Moving Parts. The Crankcase Atmosphere Is Thus Full Of Small Droplets Of Oil Under Normal Working Conditions. In Case There Develops A Hotspot E.g. Due To An Overheated Bearing Or A Mechanical Contact Between Moving Parts, The Oil In Contact And In Immediate Vicinity May Evaporate. Upon Moving Away From The Hot Spot, The Oil Vapors Will Condense Forming An "oil Mist" The Process Will Continue As Atmosphere Becomes Richer And Richer In Oil Mist I.e. Concentration Of Oil Mist Increases. At Low Concentrations, The Mixture Is Too Lean To Ignite. However, A Point Is Reached When The Mist Is Rich Enough To Ignite. This Is Called "lower Explosive Limit". After The Lower Ignition Point Is Reached, Whether The Mist Will Ignite Or Not Will Depend On The Temperature Of The Hotspot. If The Temperature Is High Enough, The Oil Mist Will Ignite And Explosion Will Take Place Which May Be Quite Mild Or Very Severe Depending Upon Oil Concentration Of Mist.

Q. What Are The Indications For Crankcase Explosion?
Ans: Indications For Crankcase Explosion Are As Follows: 
1. Bearing High Temperature Alarm. 
2. High L.o. Return Temperature. 
3. Hot Crankcase Door.

Q. What Are The Safeties In Case Of A Crankcase Explosion?
Ans: Safety For Crankcase Are: 
1. Oil Mist Detector Alarm. (set At Around 0.1% Of LEL) 
2. Bearing High Temperature Sensor Alarm. 
3. Breather Pipe To Release Excess Oil Mist Vapour. 
4. Crankcase Relief Door Fitted With Relief Valve Arrangement. 
5. Flame Arrestor For Not Allowing The Alarm To Spread. 
6. Flame Deflector To Deflect The Flame From Impinging On Any Person Standing In Vicinity.


Q. What Is The SOLAS Requirement For An Explosion Relief Valve?
Ans: The SOLAS Requirement For An Explosion Relief Valve Is That It Is Required In All Engines With Cylinder Bore Of 200mm Or Above Or With Crankcase Gross Volume Of 0.6cubic Meter. Free Area Of Each Valve Is To Be Minimum 45sq. Cm. Aggregate Area Of All Valves To Be 115sq. Cm/cubic Meter. Maximum Lifting Pressure Is 0.2 Bar. 
Alternate Relief Valves Are Also Required For Separate Gear Case Or Chain Case Spaces If Volume Of Chain Case Is More Than 0.6 Cubic Meters.