Question Answer For Marine Engineering Practise (MEP)
What Are The Alarms And Trips On A Lub Oil System For The Main Engine?
Alarms And Trips On A Lub Oil System On A Main Engine Are As Follows:
High Lub Oil Temperature Alarm
Low Lub Oil Pressure Alarm
High Lub Oil Filter Differential Alarm
Low Lub Oil Sump Level Alarm
Low Lub Oil Pressure Shut Down Alarm
Stand By Lub Oil Pump Cut In Alarm.
What Interlocks Are There On The Start Air System?
An Interlock To Prevent Fuel Being Injected
An Interlock On Turning Gear And
An Interlock CCP System, Pitch Has To Be On Zero Before Starting Engine.
Why Is Simultaneous Injection Of Fuel Oil And Starting Air Into A Main Engine Cylinder Undesirable And How Is It Prevented?
Simultaneous Injection Of Fuel And Starting Air Into A Cylinder Is Undesirable As It Could Lead To An Explosion In The Start Air System.
It Is Prevented By Means Of Interlock, Which Prevents Fuel Being Injected When The Air Start Auto Valve Is Open.
The Interlock Operates A Stop Solenoid, Which Keeps The Fuel Rack At Zero Position.
Name Main Engine Shutdowns.
Low Lub Oil Pressure
High Jacket Water Temperature
High Main Bearing Temperature
Overspeed
Oil Mist Detection
How Does The Overspeed Trip Work?
The Overspeed Trip Works By Shutting The Fuel Off To The Engine.
There Are Various Types Of Trips, Mechanical Types, Which Work On The Principle Of Fly-weights, Or Electrical Types, Which Work On The Principle Of A Speed "pick-up" Operating A Stop Solenoid.
How Does An Oil Mist Detector Work?
The Oil Mist Detector Uses A Photoelectric Cell To Measure Small Increases In Oil Density. A Motor Driven Fan Continuously Draws Samples Of Crankcase Oil Mist Through A Measuring Tube. An Increased Meter Reading And An Alarm Will Result If Any Crankcase Sample Contains Excessive Mist When Compared To Either Clean Air Or To The Other Crankcase Compartments. The Rotary Valve, Which Draws The Sample, Then Stops To Indicate The Suspect Crankcase Compartment.
The Alarm Will Cause An Engine Slow Down Or Shut Down.
What Is The Critical And Barred Range On An Engine?
This Is Where The Speed Of An Engine In Rpm, At Which The Resonant Condition Occurs, And Is Referred To As Critical Speed.
The High Stresses Associated With Resonant Condition Start To Build Up As Critical Speed Is Approached And Do Not Come Back To A Safe Value Until Speed Is Beyond Critical Speed. The Unsafe Stresses Either Side Of Critical Speed Are Known As Flank Stresses, This Is Known As The Barred Speed Range.
The Engine Must Not Be Continuously Operated At Speeds Within The Barred Range.
What Is The Purpose Of The Crankcase Oil Mist Detector?
The Purpose Of The Oil Mist Detector Is To Detect The Building Up Of Oil Mist In The Crankcase, Generated From A Hot Spot. The Detector Will Then Give An Alarm, Either Shut Down Or Slow The Engine Down And Give Indication Of Which Unit The Oil Mist Is Generated.
What Is Crankcase Inspections Frequency, Procedure And Reasons They Are Carried Out?
The Frequency May Vary From Different Engine Manufacturers But Is Roughly Around 5000 Hrs.
Also Inspections Are Carried Out After Any Work Has Taken Place In The Crankcase.
Procedure Is As Follows:
Remove Crankcase Doors From Both Sides Of The Engine. Relief Valves Can Be Checked At The Same Time As The Doors Are Off.
Inspect Condition Of All Bolt Locking Devices, Replace Any Damaged Components.
Turn Engine Over Using Turning Gear, ENSURE NO-ONE Is In Crankcase While Doing This And That The Indicator Cocks Are Open, Check Condition Of Camshaft Drive Gears.
Start Main Lub Oil Pump And Check Oil Flow From Bearings And Piston Cooling Parts. Check For Any Leakage From Internal Oil Pipes And Galleries.
Check For Any Damage Of Camshaft Lobes
Check For Any Evidence Of Water Leakage From Lower Cylinder Liner "O" Rings.
Replace Any Damaged Crankcase Door Joints.
Record Any Defects.
What Safety Devices Are Fitted To The Main Engine Crankcase?
Explosion Door/Relief Valves, Bearing Temperature Sensor And Oil Mist Detectors.
What Are Crankcase Pressure Relief Valves For?
These Valves Act As A Safeguard To Relieve Excessive Crankcase Pressures, Which May Occur From Oil Vapour Igniting In The Occurrence Of An Engine Component Overheating. They Also Prevent Flames From Being Emitted From The Crankcase And Must Also Be Self Closing To Stop The Return Of Atmospheric Air Into The Crankcase.
What Would Cause A Crankcase Explosion?
A Crankcase Explosion Could Be Caused By The Formation Of A Hot Spot I.e. The Overheating Of A Bearing, Which In Turn Could Cause An Oil Mist To Be Generated. If This Oil Mist Is Allowed To Build Up, An Explosive Condition Could Occur Where The Oil Mist Can Be Ignited By Piston Blow By Or The Hot Spot Itself.
What Would You Do In The Case Of A Crankcase Explosion?
When The Alarm Sounds, The Engine Speed Must Be Reduced To Slow And Permission Obtained To Stop The Engine.
Inform Chief Engineer.
When An Engine Has Stopped Under Alarm Conditions Under No Circumstances Must Any Doors Or Inspection Windows Be Opened.
Oil Should Continue To Be Circulated And Time Allowed For The Hot Spot To Cool.
The Early Opening Of Doors Could Cause An Explosion Due To Ingress Of Air.
During Cooling Down Period, The Engine Room Staff Must Keep Clear Of The Side Of The Engine Fitted With Explosion Doors.
After A Period Of At Least 20 Minutes, Stop The Lubricating Oil Pump, Cut Off All Air And Engage Turning Gear.
The Access Doors Should Then Be Opened And Personnel Must Keep Clear Of Possible Flames. Under No Circumstances Should Naked Lights Be Used Nor Should Anyone Be Permitted To Smoke.
Examination Should Then Take Place For Any Squeezed Out Bearing Metal Or Loose Bearing Metal In The Crankcase. Heat Discoloured Metal Parts Or Blistering Of Paintwork Must Be Investigated. The Ceiling Of The Crankcase And Guide Bars Should Also Be Observed. If The Crankcase Is Clear, The Camshaft Drive And Main Thrust Bearing Should Be Inspected For Signs Of Overheating.