Category: Marine Tech

Here Are The Change Over Questions And Answers Which Will Help You To Understand So Many Things –

Question: What Do You Mean By Change Over? Why It Is Required On-board?
Answer: Changeover Of An Engine Is Related To Change The Fuel Oil On Which It Is Operating. It May Be From Diesel Oil To Heavy Or Vice Versa. Due To Greater Cost Of Diesel Oil It Is More Economic To Run Engine On Heavy Oil. But During Long Port Stay Or Where Environmental Legislation Requires The Use Of Low Sulphur Fuels, Diesel Oil Is Used. Hence Engine Often Requires Changing Over From One Type Of Fuel To The Other.

Question: Is There Any Difference In Change Over Procedure For An Engine With Mixing Column And An Engine Without It?
Answer: Yes, There Are Some Differences In The Change Over Procedures For An Engine With A Mixing Column And An Engine Without Mixing Column.

Question: What Are The Steps Involved During Change Over From Diesel Oil To HFO For A Running Engine?
Answer:
Engines Without Mixing Column
1. Heavy Oil Is Heated To 75 Degree C In The Heavy Oil Service Tank. 2. By Means Of Thermostatic Valve In The Steam Line Or Manual Control Of Viscosity Regulator, Diesel Oil Is Heated To About 60 Degree C. This Pre Heating Should Be Regulated With A Temperature Rise 1-2 Degree C/minute. 3. Reduce Engine Load To Harbor Full And Change Over To HFO. 4. Now Raise The Temperature Of HFO At A Rate Of 1-2 Degree C/minute To The Proper Service Temperature Of The HFO. 5. Maintain The Service Temperature And Raise The Engine Load Gradually.

Engines Fitted With Mixing Column.
1. With Mixing Tank Change Over From Diesel Oil To Heavy Oil May Be Done At Full Engine Rpm. 2. Start Circulating Pump Of Mixing Tank. 3. Set Change Over To Heavy Fuel Oil. 4. Open Steam Supply To The Pre-heater.

Question: What Are The Steps Involved In Change Over From Heavy Oil To Diesel Oil For Running Engine? 
Answer:
Engines Without Mixing Column 
1. Cutoff The Stem Supply To Pre-heater. 2. Reduce Engine Load To Harbor Full. 3. As The Heavy Oil Temperature Drops By 5 Degree C. 4. Change Over To Diesel Oil. If Temperature Suddenly Drops Considerably, It Must Be Moderated By Supplying Steam To Pre Heater.
Engines Provided With Mixing Column
1. It Can Be Done At Full Load Condition. 2. Keep Circulating Pump To Mixing Tank On. 3. Set Change Over To Diesel Oil. 4. Close Steam Supply To The Pre-heater.

Here Are The Exhaust Gas Questions And Answers Which Will Help You To Understand So Many Things –

Question: What Are Main Constituents Of Exhaust Gas, Its Effect And Technology Used To Reduce Them?
Answer: All Marine 2-stroke Diesel Engines Uses Low Quality Of Fuel To Reduce The Cost. This Low Quality Of Fuel Tends To Have Many Impurities. However Some Of Those Can Be Separated By Use Of Centrifuges But Some Residuals Are Unavoidable. In Order To Prevent Atmospheric Pollution And Its Impact On Human Health And Climate Change. There Are Several Limitations Have Been Imposed By National, Regional And International Authorities To Control The Air Pollution.

Constituents Of Exhaust Gas:
NOx- Formation Of Nitrogen Oxides Is Due To Combination Of Nitrogen And Oxygen From Air At Higher Combustion Temperature. These Oxides Are Regarded As Carcinogenic Compounds And Contribute To Photo-chemical Smog Formation And Acid Rains.
Impacts:
1. Cause Acid Rain Thus Acidification Of Soil.
2. Affects Air Quality.
3. Elevates The Level Of Ozone And Produces Hazardous Organic Compounds.
4. Cause Green House Effect At Low Temperature.

Technology To Reduce NOx
1. Modification Of Combustion Process:
I) Increasing Injection Pressure, Delaying Injection Timing
Ii) Increasing Compression Ratio
Iii) Alteration Of Air – Fuel Ratio
Iv) Optimization Of Induction Swirl
V) Increasing No. Of Injectors And Modification In Its Design

2. Modification In Air Intake System
I) Scavenge/charge Air Cooling
Ii) Increasing Scavenge/charge Air Pressure

3. Direct Water Injection: It Reduces NO Discharge By 50 To 60 %

4. Exhaust Gas Recirculation: It Reduces Oxygen By 15 % Thus Reduction In NOx Formation

5. Humid Air Motor (HAM): Dilution Of Charge Air By Water Reduces NOx By 70 %. But This Is Not A Very Effective Method For NOx Reduction. Use Of HAM Increases SFOC And Produces Smoke. There Is Also High Investment Cost And One Important Disadvantage Is It Reduces The Net Energy Available At T/C.

6. SCR: Selective Catalytic Reduction Is Widely Used For The NOx Reduction And Reduces 85-95 % And Doesn't Affect Engine Performance. In SCR Method Exhaust Gas Is Mixedwith NH3 And Passed Through A Layers Of Catalyst At 300 – 400 Degree C To Reduce NOx Into N2 And H2O.

SOx – Oxides Of Sulphur Produced During Due To Combustion Of Sulphur In The Fuel. Amount Of SOx Formation Depends Upon The Concentration Of Sulphur In The Fuel Oil. The Prime Constituent Of SOx Is SO2. It Has Very Adverse Effect On Health And Atmosphere. Impacts: 1. It Has Unpleasant Order And Irritates Mucus Membrane. 2. It Is A Major Source Of Acid Rain. 3. Sufficient Concentration Of SO2 Can Adversely Affect The Lungs Function. Technology To Reduce SOx 1. Use Of Scrubbers Can Remove Majority Of SOx Emission From The Exhaust. 2. Use Of Low Sulphur Fuel (most Efficient Method To Reduce SOx Emission). 3. Speed Reduction: Reduction In Speed By 10 % Gives 20 % Reduction In Fuel Consumption Over Same Distance.

HC (Hydrocarbons) – It Is Produced Due To Incomplete Combustion Of Fuel. It Has Unpleasant Order And Carcinogenic Compound. However Amount Of HC Is Very Low If Combustion Is Proper.

CO – It Is Formed Due To Incomplete Combustion I.e. Due To Local Shortage Of Air During Combustion. It Is Highly Toxic Compound And It Is Very Hazardous At Higher Concentration.

Question. What Do You Mean By Auxiliary Engines?
Answer: Auxiliary Engines Are Those Engines Which Are Not Used For Propulsion, Rather The Power Produced By These Engines Is Used In Generation Of Electricity.

Q. How Do Auxiliary Engines Provide Electricity?
Ans: Actually These Auxiliary Engines Onboard Are Coupled With Alternators Which Convert The Mechanical Power/energy Produced By Auxiliary Engines Into Electrical Power/energy.

Q. Define The Various Parts Of An Auxiliary Engine?
Ans: An Auxiliary Engine Consists Of Various Parts: 
A) Cylinder Head: Cylinder Head Consist Of Exhaust Valve, Inlet Valve, Indicator Cock, Fuel Injector, Starting Air Valve Etc. 
A) Cylinder Liner 
B) Piston Assembly : It Consists Of A Piston, Made In Two Parts Upper Part Is Piston Crown And The Lower Is Piston Skirt , Two To Three Compression Rings Are Fitted In The Ring Grooves Of Piston Crown Where As An Oil Scraper Ring Is Fitted In Ring Groove Of Piston Skirt. 
C) Gudgeon Pin Bearing Assembly: At The Mating Point Of The Connecting Rod And Piston Skirt, This Gudgeon Pin Bearing Assembly Connects Both Of Them. 
D) Bottom End Bearing Assembly: Bottom End Or Crank Pin Bearing Assembly Joins The Connecting Rod To The Crank Journal Vis-a-vis Crankshaft. 
E) Crankshaft: Generally Semi Built Type Crankshafts Are Used These Days Which Are Lighter And Durable. There Are Drilled Passages Through The Crankshaft For Lubrication.

Q. Explain The Lub Oil Diagram For An Auxiliary Engine?
Ans: The Lub Oil Diagram For Auxiliary Engine Is As Follows: Description: There Is Only One Type Of Oil Used For Both Cylinder And System Lubrication In Auxiliary Engines Where As In Main Engine Separate Cylinder And System Oils Are Used . When The Auxiliary Engine Is Not Running Then A Motor Driven Priming Pump, Pumps Lub Oil From Sump To Different Parts Such That Seizure Of Parts Doesn't Take Place. When Auxiliary Engine Is Started, The Shaft Driven Gear Pump Comes Into Action And Draws Oil From Sump Via A Strainer. The Lub Oil Further Moves Under The Pressure Generated By The Gear Pump To The Lub Oil Cooler, There Is A Separate By-pass Line For Centrifugal Filter Which Cleans The Oil From Sump To Sump. From Cooler, The Oil Moves To The Main Gallery For Distribution Through A Notch Wire Filter. In The Main Gallery This Lub Oil Is Transferred To Various Parts Like Turbocharger For Bearing Lubrication, Camshaft Gears, Main Bearing, Fuel Injection Pump Tappet Roller, Suction And Exhaust Valve Rocker Arm Lubrication Etc. After Lubrication This Lub Oil Drains From All These Parts To The Sump.

Q. List Various Properties Of The Lub Oil Used In Auxiliary Engines And How Is It Different From The Lub Oil Used In Main Engine?
Ans:
Viscosity: It Is A Measure Of Internal Resistance To Flow Of Fluids. Higher The Viscosity, The Greater Will Be Internal Resistance To Flow. If The Viscosity Of Lub Oil Is Too Low It May Not Be Possible To Maintain Sufficient Fluid Film Thickness For Avoiding Metal To Metal Contact. In Commercial Marine Applications, Viscosity Of Lubricating Oil Is Specified In SAE(Society Of Automotive Engineers)units. Typical Values Are SAE 30 For Crosshead Type Engine Bearings (equivalent To 9.3 To 12.5cst At 100 Deg Celsius) And SAE 40 For Trunk Piston Bearings (equivalent To 12.5 To 16.3 Cst). For Cylinder Lubrication, SAE 50 (equivalent To 16.3 To 21.9 Cst) Is Normally Specified. 

Demulsification: Demulsification Is The Opposite Of Emulsification I.eit Is The Separation Of Water From Oil. More The Demulsibility, The More Easily The Water Separates Out From Oil.

TBN(Total Base Number): It Is Expressed In Terms Of Number Of Mg Of KOH Required To Neutralize The Acid Present In One Gram Of The Lub Oil It Is One Of The Most Important Properties For Cylinder Lubrication. The TBN Value Of Lub Oil For Auxiliary Engines Is 15 To 30. 

Anti Oxidation: Oxidation Is A Common Form Of Deterioration Of Lub Oil In Service. Oxidation Takes Place At High Temperature In The Presence Of Air And Certain Contaminants Such As Rust, Sludge, Metal Wear Particles Such As Iron, Copper And Lead All Of Which Act As Catalysts. Oxidation Gives Rise To Sludge Formation And If Allowed To Continue Unchecked, It May Proceed At An Increasing Rate Eventually Causing Blockage Of Filters, Purifiers Etc. Stability Is The Property Of Oil That Resists Oxidation. To Ensure Oxidation, Good Base Stock Oil With Suitable Anti-oxidation Additives Should Be Used. 

Dispersancy: It Is The Ability Of The Oil To Maintain Insoluble Particles In Such A Finely Divided Condition That They Do Not Settle Out And Deposit As Sludge On The Colder Engine Surfaces. Dispersancy Is Ensured By Adding Dispersant Additives To The Oil. 

Detergency: Detergency Of The Lub Oil Is Its Property Of Being Able To Keep Interior Parts Of The Engine Clean And Free Of Deposits. Detergent Additives Include Metallo-organic Compounds Of Sodium, Calcium, And Magnesium, Phenolates, Phosphonates And Sulfonates. These React Chemically With Sludge To Neutralize And Keep Them Oil Soluble.

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.

Question: What Is A Bearing? 
Ans: Generally Speaking, A Bearing Is A Device That Is Used To Enable Rotational Or Linear Movement, While Reducing Friction And Handling Stress. Resembling Wheels, Bearings Literally Enable Devices To Roll, Which Reduces The Friction Between The Surface Of The Bearing And The Surface It's Rolling Over. It's Significantly Easier To Move, Both In A Rotary Or Linear Fashion, When Friction Is Reduced, This Also Enhances Speed And Efficiency.

Q. What Type Of Bearings Is Generally Used In Marine Diesel Engines?
Ans: Multi Layer Thin Wall Shell Type Bearings Are Used Widely In Marine Diesel Engines. These Are Usually Tri-metal Bearing. Babbitt Metal Lacks Fatigue Strength. It Breaks Down Under Load. The Durability Of Babbitt Greatly Increases As The Material Decreases In Thickness. The Common Solution Is To Apply A Thin Layer Of Babbitt Over A Supporting Layer Of Copper/lead Which Acts As A Cushioning Layer And Allows For Slight Misalignment.

Q. What Do You Mean By Thin Shell Bearing? Why Thin Shell Bearings Are Used Instead Of Cast Type, In Modern Marine Diesel Engine?
Ans: Thin Shell Bearings Are Most Common Bearings Used In Modern Main Engines. They May Be Bi-metal Or Tri- Metal Bearings. Typical Materials For Bearings Are Steel-babbitt, Steel-bronze Or Steel-tin/aluminum ( Tin-aluminum Has Slightly Greater Load Bearing Capacity Than White Metal And Maintains Its Fatigue Strength Over A Greater Range Of Temperatures. It Consists Of A Steel Backing Strip Coated With A Layer Of White Metal. The Bearing Metal Thickness Is 0.5 To 3mm. An Overlay Of 20 -40 Micrometers May Be Applied To Improve Conformity. This Is Generally A Ductile Coating Of Lead And Tin. In Addition New Bearings May Have A Flash Layer Of A Few Microns Of Tin To Prevent Oxidation. An Intermediate Layer May Be Used Between The Overlay And Main Bearing Metal To Avoid Diffusion. This Is Particularly Found Where Bearing Loads Are Very High Such As In The Lower Half Of The Cross Head Bearing.

Q. Which Material Is Used In The Bearing Of Marine Diesel Engines?
Ans: Materials Used For Bearing Of Large Marine Diesel Engines Are: 
Tin Based White Metals / Babbitt Metal: 
Tin-based White Metal Is An Alloy With Minimum 88% Tin (Sn), The Rest Of The Alloy Composition Is 8% Antimony (Sb), 4% Copper (Cu). Cadmium (Cd) And Small Amounts Of Other Elements That Are Added To Improve The Grain Structure, Homogeneity During The Solidification Process. This Is Important For The Load Carrying And Sliding Properties Of The Alloy. Lead (Pb) Content In This Alloy Composition Is An Impurity, As The Fatigue Strength Deteriorates With Increasing Lead Content, Which Should Not Exceed 0.2 % Of The Cast Alloy Composition. Tin Based White Metal Is Used In The Main Bearings, Crankpin Bearings, Crosshead Bearings, Guide Shoes, Camshaft Bearings And Thrust Bearings Because Of Its Excellent Load Carrying And Sliding Properties. 
Tin And Aluminum Based Bearings: 
Alloys Containing 20 To 40% Tin, Remainder Aluminum, Show Excellent Resistance To Corrosion By Products Of Oil Breakdown. The Sliding Properties Of This Composition Are Very Similar To Those Of Tin Based White Metal But The Loading Capacity Of This Material Is Higher Than Tin Based White Metals For The Same Working Temperature; This Is Due To The Ideal Combination Of Tin And Aluminum, Where Tin Gives The Good Embedability And Sliding Properties, While The Aluminum Mesh Functions As An Effective Load Absorber. The Higher-tin Alloys (40%) Have Adequate Strength And Better Surface Properties, Which Make Them Useful For Main And Crosshead Bearings For Heavy Marine Diesel Engines. Tin Aluminum Bearings Were Developed To Provide Bearings That Carry High Loads. Special Features Are Their Good Resistance To Corrosion, High Thermal Conductivity And High Fatigue Strength, But They Have The Disadvantages Of Only Moderate Embedding Properties, Poor Compatibility And High Coefficients Of Thermal Expansion. If Used As Solid Un Backed Bearings This Type Of Alloy Is Usually Too Weak To Maintain An Interference Fit And Too Hard To Run Satisfactorily Against An Unhardened Shaft. Considerable Improvement In Anti- Scoring Characteristics And Embedability Is Obtained By Using A Thin-lead Babbitt Or Electrodeposited Lead-tin Overlay. 
Lead Bronze Based Bearings: 
Lead Bronzes Basically Are Copper-tin-lead-alloys. They Are Used In Very Highly Loaded Bearings Because Of Their High Fatigue Strength; Their Drawback Is Poor Tribological Behavior. That Is Why They Require An Electroplated Overlay In Most Applications. Standard Composition For Conrod And Main Bearings Is 78 % Cu, 20 % Pb, 2 % Sn. The Alloy Is Used With Electroplated Overlay Or Cast Babbit Running Layer. These Bearings Can Be Found In Marine Medium Diesel Speed Engines.

Q. Why Thin Shell Bearings Are Used Instead Of Cast Type, In Modern Marine Diesel Engine?
Ans: Compared With The Traditional Cast Bearing, Thin Shell Bearings Have A Number Of Advantages. Shells Are Prefinished Thus Allowing For Quicker And Easier Replacement. The Bearings Are Made Under Strict Controlled Conditions Giving Consistent High Quality Products In Many Cases The Top And Bottom Halves Are Interchangeable In An Emergency. Thin Layer Of White Metal Cools Quickly Giving Fine Grain Structure Which Has High Strength And Fatigue Resistance.

Q. What Are The Different Layers Found In Modern Tri-metal Bearings? Give Brief Description?
Ans: A Modern Tri-metal Bearing In Fact Have Multi Layers And A Steel Back Supports Bearing Structure, Provides Its Rigidity And Press Fit Under Severe Conditions Of Increased Temperature And Cycling Loads. 
The Main Layers In Modern Diesel Engine Bearings: 
1. Flash Layer: A Flash Layer Is A 100% Tin (Sn) Layer Which Is Applied Galvanically. The Thickness Of This Layer Is From 2 Microm To 5 Micro M. The Coating Of Tin Flash Is Applied All Over And Functions Primarily To Prevent Corrosion (oxidation) Of The Bearing. The Tin Flash Also Functions As An Effective Dry Lubricant When New Bearings Are Installed. 
2. Overlay/ Tri-metal : An Overlay Is A 20 Micro Meter Thick White Metal. The Overlay Is A Soft And Ductile Coating. Its Main Objective Is To Ensure Good Embedability And Conformity Between The Bearing Sliding Surface And The Pin Surface Geometry. 
3. Interlay: An Intermediate Layer May Be Used Between The Overlay And Main Bearing Metal To Avoid Diffusion. This Is Particularly Found Where Bearing Loads Are Very Such As In The Lower Half Of The Cross Head Bearing. It Is 5 Micro Meter Thick Nickel Diffusion Barrier (nickel Dam) Is Deposited Between The Overlay And Main Bearing In Order To Prevent Corrosion Of White Metal. 
4. Bonding Layer: Is Used For Good Adhesion Between The Steel Back And Aluminum-tin Alloy. Presence Of Tin Particles On The Surface Of An Aluminum-tin Alloy Bonded To A Steel Strip Weakens The Adhesion Strength Between The Materials. A Bonding Layer Of Pure Aluminum Between The Aluminum -tin Alloy And Steel Allows Achieving Strong Adhesion. Pure Aluminum Is Commonly Bonded To The Aluminum-tin Alloy And Then The Aluminum Strip Is Bonded To Steel Back. The Thickness Of The Aluminum Bonding Layer In A Bearing Is About (25-50 Micro Meter). Another Type Of Bonding Layer Is A Nickel Layer Deposited On The Steel Surface Prior To Bonding With Aluminum-tin Alloy. 
Another Type Of Bonding Layer Is A Nickel Layer Deposited On The Steel Surface Prior To Bonding With Aluminum-tin Alloy.

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.

Question: What Is A Purifier And State Its Purpose?
Answer: A Centrifugal Purifier Is Essentially A Container Which Is Rotated At High Speed While Contaminated Oil Is Forced Through, And Rotates With The Container. However, Only Material That Are Insoluble In The Oil Can Be Separated By Centrifugal Force, Distillate E.g., Gas Oil Cannot Be Separated From Lubricating Oil, Nor Salt Can Be Removed From Sea Water By Centrifugal Force. Water Can Be Separated From Oil Because Water And Oil Does Not Form A True Solution When They Are Mixed. Furthermore, There Must Be A Difference In The Specific Gravities Of The Materials Before They Can Be Separated By Centrifugal Force.

When Separation Process Is Required, Two Conditions Could Be Met: 
1.    To Separate Solid Particles From A Liquid, E.g. Sludge / Dirt From Oil. 
2.    To Separate Liquids Of Different Densities Which Are Mutually Insoluble E.g. Water From Oil 
Purpose Of Purifier Is To Purify Oil And Remove Dissolved Impurities. Oil That Is Fed Into An Engine Requires Controlled Characteristics To Maintain The Engine Operational Reliability And Extend The Life Usage.An Oil Purifier Separates Various Contaminants (Aluminum, Silicon, Sludge, Water, Etc.) From Oil In Such Specific Condition To Maintain Oil Characteristics To Certain Limits.

Q. State The Principle Of Centrifugal Purifier? 
Ans: When Centrifugal Force Is Applied, The Main Separating Force Is Equal To The Difference Between The Centrifugal Force Acting On The Solid And Water, And The Centrifugal Force Acting On The Oil Due To The Difference In The Density. 
As Per Stoke's Law, The Separating Force In Centrifugal Separation Can Be Expressed:
F= (pid3v2/6r) X (d2-d1) 
Where: 
D = Diameter Of Particle 
V = Linear Velocity Of Particle 
R = Radius Of Rotation Of Particle 
In The Formula Above, The Separating Force Acting Between The Two Liquids Or Liquid And Solid Particle Is Directly Proportional To The Difference In Their Densities And The Square Of Linear Velocity. This Method Of Separation Is Very Useful When The Difference In Densities Of Water And Oil In A Mixture Is Very Less. Since The Separation Force Is Directly Proportional To Square Of Linear Velocity, It Can Be Increased Many Fold By Rotating The Container At Permissible High Speed.

When A Centrifugal Force Is Acting In The Rotating Container, All Solid Particles And Water Which Is Heavier Than Oil Is Displaced Outward From The Center Of Rotation. The Lighter Liquids Tend To Form In The Center And Moves Upward. Centrifugal Force Application Increases The Separation Process In A Rotating Container. 
In A Centrifugal Purifier, The Separated Water Is Discharged From Water Outlet, The Oil From The Clean Oil Outlet And The Solid Remain In The Rotating Unit. The Separation By Centrifugal Force Is Further Affected By The Size Of The Particles, The Viscosity Of The Fluids, And The Time During Which The Materials Are Subjected To The Centrifugal Force. In General, The Greater The Difference In Specific Gravity Between The Substances To Be Separated And The Lower The Viscosity, In Case Of Fuel Oil The Greater Will Be The Rate Of Separation.

Q. What Is Interface And Why It Is Important? 
Ans: The Interface Is The Boundaries Of Layers Between The Separating Liquid And It Is Important To Maintain Inside The Bowl Of The Centrifugal Separator To Attain The Effectiveness Of Purification. If The Separator Is Running As Purifier, It Is Necessary To Hold The Oil And Water Interface In The Bowl Within The Definite Range. The Position Of Interface Is Controlled By Varying The Outlet Diameter Of The Heavy Liquid (water) Side And Achieved By Using Gravity Discs Of Different Inside Diameters.

Q. What Are The Factors Affect The Position Of Interface? 
Ans: 
1.    Size Of The Gravity Disc 
2.    Density Or Specific Gravity Of Oil 
3.    Viscosity Of Oil 
4.    Oil Inlet Temperature And 
5.    Oil Feed Rate

Q. What Are The Factors Required Maintaining The Correct Position Of Interface? 
Ans: 
1. Correct Size Of Gravity Disc. 
2. Clean Disc Stack. 
3. Maintain The Following Feed Condition: 
4. Constant Oil Properties I.e. Viscosity & Density 
5. Constant Flow Rate 
6. Constant Temperature

Q. What Are The Factors Effects The Selection Of A Gravity Disc? 
Ans: 
The Selection Of The Gravity Disc Depends Upon The Following Factors: 
1.Specific Gravity Of Feed Oil 
2.Feed Rate 
The Adjustment Of Feed Rate Is Mainly Governed By Daily Consumption (as In Fuel Oil) And The Effectiveness Of 
Separation/purification Desired (as Normally Applied For Lube Oil). The Recommended Feed Rate For The Following: 
I) For Fuel Oil, It Is Recommended That The Separator Should Operates At About 50~70% Of The Rated Capacity. In Case That The Fuel Oil Quality Is Over Specification And Its Properties Exceed Company Specifications, It Is Recommended To Operate Available Purifiers In Parallel Operation And Reduce The Feed Rate To About 30% For Each Purifier. 
Ii) For Lube Oils, The Recommended Feed Rate Is The Minimum Possible Feed Rate At Which Separation Temperature Can Be Maintained. This Minimum Feed Rate Will Help In Removing The Finer Impurities. For A Continuous Separation System, It Is Better To Circulate The Full System Oil Through The Separator 5~6 Times/24 Hrs Rather Than Circulating It 10~15 Times/24 Hrs With Increased Feed Rate. 
The Minimum Feed Rate Is Limited By The Controllability Of Constant Temperature. When The Feed Rate Is Changed Drastically, It Is Necessary To Recheck Whether The Gravity Disc Is Appropriate And Replacement Is Required, As Feed Rate Is One Of The Governing Factors In The Selection Of Gravity Disc. 
3.Oil Inlet Temperature 
The Oil Should Be Heated To Obtain An Appropriate Reduction In Viscosity And Specific Gravity As To Effect An Efficient And Quick Separation Of Water And Other Impurities. However, The Oil Temperature Should Be Maintained Less Than 100 Degree C To Avoid Evaporation Of The Sealing Water And Damage To O-rings. 
The Treating Capacity Of The Oil Purifier Depends Mainly On The Viscosity Of Feed Liquid And Can Be Plot On The Temperature-Viscosity Diagram Below. To Ensure That The Oil Purifier Operates Efficiently, Heat The Feed Liquid To Specified Temperatures As Follows:

Q. Why Scavenge Inspection Is Done And What Are The Things Should Be Checked During Inspection?
Ans. Scavenge Inspection Is The One Of The Most Efficient Method Used Onboard To Determine Engine's Running Condition. It Provides Us All The Useful Information Like Condition Of Cylinder Liner, Piston, Rings, Piston Rod, Skirt Etc. At Almost Zero Expense.

Things Should Be Checked During Scavenge Inspection. 
1.    Keep Cooling Oil And Cooling Water Circulation On And Check For Any Leakage. 
2.    Inspect The Scavenge Air Box And Ports For Any Sludge Accumulation And Ensure Scavenge Drains Are Clear. To Reduce The Risk Of Scavenge Fire, Remove Any Sludge And Carbon Deposits In The Scavenge Box. 
3.    Inspect The Condition Of Piston, Piston Rings, Liner, Piston Rod And Skirt. It Should Be Visually Examined Through Scavenge Air Ports. Check Piston Crown For Burning Marks And Deposits. Check Skirt For Scuffing Marks And Abrasion. In Good Running Conditions, The Running Surfaces Of The Piston Rings And Cylinder Liner Will Be Worn Bright. Rings Should Move Freely In The Grooves And Should Be Well Oiled. Press The Piston Rings Inside The Groove And If It Pushes Back Then Its Intactness Is Confirmed. 
4.    Check All Non Return Valves/flap Valves In The Scavenge Air Box For Their Easy Movement And Possible Damage. 
5.    Inspect All Mountings On The Scavenge Box. Scavenge Relief Valve Should Be Examined And Should Be Cleaned. Temperature Probe Should Be Inspected And All Deposits Should Be Removed.

Question: What Is An Air Bottle/receiver? What Is Its Purpose And Capacity For Onboard Use
Answer: An Air Bottle Is A Storage Unit Where Compressed Air, At Pressure Around 28-30 Bar Supplied By Air Compressor Is Stored. The Major Purpose Of Storing The Compressed Air In Air Receiver Is To Use It For Starting The Main Engine And Auxiliary Engine. According To SOLAS, An Air Bottle Must Be Capable Enough To Provide 12 Consecutive Starts For A Reversible Engine And 6 Consecutive Starts For A Non-reversible Engine. This Is Known As The Capacity Of An Air Bottle.

Q. What Are The Mountings On An Air Bottle?
Ans: List Of Air Bottle Mountings: 
1. Relief Valve: It Is The Most Important Mounting On The Air Bottle , Generally On Top Of The Receiver, In Case Of Excessive Or Sudden Pressure Rise More Than 10% Of The Air Bottle Capacity, These Relief Valve Lift And Release Excess Air, Then Sit Back. 
2. Fusible Plug: In Case Of Engine Room Fire If The Temp Rises Above 150 Degree C, The Fusible Plug Melts And Through A Separate Connection Releases Air Into The Atmosphere Outside Engine Room Such That, The Air Bottle Doesn't Burst And Infuriate The Engine Room Fire. 
3. Drain Valve: Generally, There Are Two Drain Cocks Fitted Adjacent To Each Other Such That If One Gets Chocked Other Can Drain The Air Bottle. 
4. Pressure Gauges: Correctly Calibrated Gauges Must Be Used And Pressure Must Lie Within 27-30 Bar Which Is Required Pressure For Starting Main And Auxiliary Engines. 
5. Main Valve For Starting Air To The Main Engine: It Is A Sluggish Opening Valve So That A Sudden Pressure Surge In The Start Air Line Is Avoided; Otherwise Start Air Line Might Burst. 
6. Valve For Start Air To Auxiliary Engines: To Supply Air To Start Auxiliary Engines. 
7. Inlet Valve From Main Air Compressor: To Fill Air Bottles/receiver. 
8. Manhole Door: Elliptical Door For Entry Of A Person For Air Bottle Inspection.

Q. Mention If There Are Any Alarms In Air Bottle?
Ans: Air Bottle Low Air Pressure Alarm Is Most Significant Alarm In The Receiver. When This Alarm Is Activated, Starting Of Main And Auxiliary Engine Is Not Possible. This Alarm Implies That There Is Not Enough Air In The Bottle.

Q. What Is Most Important Routine We Have To Carry Out Every Watch On Air Bottle And What Are Its Implications?
Ans: Every Watch During Rounds We Must Drain The Air Bottle. We Must Keep The Drain Cock Open Until All The Moisture Is Drained. If Not Drained Regularly, It May Have Disastrous Results. 
1. If Oil Carryover From Compressor Is Taking Place Then Chances Of Catching Fire Is Evident As Heat Is Only Element Left Which Is Required To Complete The Fire-triangle. 
2. If Moisture Carryover Along With Compressed Air Takes Place, This Moisture Can Corrode The Air Bottles.

Q. What Is Material Of Air Bottle And Procedure For Air Bottle Inspection?
Ans: The Air Bottle Is Made Up Of Cast Iron. The Steps Followed For Air Bottle Inspection Are As Follows: 
1. The Drain Cocks Are Opened, So That The Bottle Is Completely Drained. 
2. When The Air Pressure In The Bottle Comes Near To Zero, Than The Manhole Door Is Opened. 
3. Thorough Ventilation Is Carried Out By Using Ventilation Fans. 
4. An Enclosed Space Entry Permit Is Being Made Under The Guidance Of Chief Engineer. 
5. Oxygen Content Is Checked Inside By Oxygen Meter, Must Be Around 20.8%. 
6. Now, A Person Can Enter With A Standby Person Standing Outside. 
The Person Inside Checks: 
A. The Walls Of Bottle For Corrosion. 
B. The Bottom For Moisture Content Or Oil Accumulation. 
C. Checks The Condition Of Compensating Rings (fitted For Compensating The Strength Lost Due To Cutting Manhole Door). 
D. Checks If Any Drain Is Blocked From Inside. 
E. Safety Valve Fitting Area. 
Sometimes, Checks Can Be Carried Out From Outside By The Help Of An Instrument Called Boroscope.

Q. Give A Brief Description About Alpha Lubricator?
Ans: Advent Of New Technology And Increment In The Prices Of Oil Forced To Cut The Running Costs Of Marine Machineries. Alpha Lubricator Can Be Considered As The Result Of The Same. It Hasn't Only Reduced The Operational Cost But Also Optimized The Engine Performance. It Is Modern Method Of Controlled And Calibrated Cylinder Lubrication. Individual Cylinder L.O. Quantity Control Can Be Achieved In Alpha Lubricators. Oil Is Supplied To The Liner Walls Through Quills And Quantity Of Oil Is Controlled By Changing Position Of Central Piston In The Lubricator Unit.

Q. What Are The Main Components Of Alpha Lubricators?
Ans: 1. Pump Station And Starter Panel: Two Pumps (individually Operating) Take Suction From Suction Tanks, Through Filters. Heating Coil Is Also Fitted In The Tanks To Ensure Inlet Temperature In Cold Time. Power Is Supplied To The Pumps Trough Two Circuit Breakers, One Supplying Each Pump.

2. Lubricator Unit: It Is Consisting Of Two Or One Lubricator (depending On Cylinder Bore). Each Lubricator Unit Equipped With One Accumulator With Nitrogen Pressure Of 25-30 Bar On The Inlet Side And One At Outlet Side With A Pre Pressure Of 1.5 Bars For Every Lubricator. A Feed Back Peak Up And Solenoid Valve Is Also Fitted In The Lubricator Unit.
3. Alpha Lubricator Control Unit (ALCU)
4. Load Transmitter: It Is Connected To The Fuel Rack, Transmitting Fuel Rack Index (%) To Master Control Unit (MCU), Calculates Engine Load And Detects Rpm.
5. Trigger System (Shaft Encoder): Shaft Encoder Is Connected At The Fore End The Fore End Of The Crank Shaft Transmits Signal To The Computer Panel. It Helps To Decide Piston Position Hence Injection Timing.
6. Back Up Trigger System: Two Tacho Pick Ups In A Box At Turning Wheel Transmitting Engine Rpm To The Back Up Control Unit (BCU). It Helps BCU To Meter Oil Amount As Per The Engine Rpm When MCU Gets Failed. It Is Also Connected To MCU For Surveillance Purpose.
7. Human Machine Interface (HMI): It Helps Engineer Officers To Do Various Adjustments And Controls.
– Lubrication Feed Rate Adjustment
– Control Of Pump Station
– Display Various Alarms
– Shows Amount Of Oil Consumed

Q. What Are The Main Advantages Of Alpha Lubricator?

Ans: 1. Reduction In SLOC (up To 0.7 Gm/Kwh) Hence Reduction In Cost.
2. Optimum Distribution Of Oil On The Cylinder Walls.
3. Less Deposits In Combustion And Scavenge Spaces.
4. Better Pre Lubrication Can Be Achieved.
5. Individual Cylinder Feed Rate Adjustment.

Q. Give A Brief Description Of Its Working Principle?
Ans: 1. Pump Supplies Oil To The Alpha Lubricators At A Pressure Of 40-45 Bar (varies According To The Cyl. Bore)
2. Injection Timing Decided By The Tacho Peak Ups And MCU Commence The Oil Injection By Activating Solenoid Valve On The Relevant Lubricator, Which Allows Oil To Flow To The Liner Walls Through Quills.
3. A Feed Back Signal By Led Confirms Oil Injection.
4. During Normal Operation System Is Controlled By MCU And If Any Failure Occurs, BCU Automatically Takes Over.

**BCU Is Based On Random Time Injection. However, Amount Of Injection Depends On The Engine Rpm. In BCU Mode Injection Is 50% Surplus Of The Normally Required At That Rpm.