CoC Oral Exam Preparation (Part- 4) – Lub Oil & Fuel Oil

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Lubricating Oil

Viscosity:
1. A measure of internal resistance to flow.
2. Viscosity of an oil changes with temperature, falling when temperature rises and vice versa.
3. For crankcase oil, viscosity is between 130 – 240 Sec. Redwood No. 1 at 60°C.
4. For cylinder oil, viscosity is 12.5 – 22 Cst.

Viscosity Index, VI:
1. The rate of change of viscosity of an oil, in relation to change of temperature.
2. Oil of low VI has greater change of viscosity with change in temperature,
than the oil of high VI.
3. For crankcase oil, VI is between 75 – 85; For cylinder oil, VI is 85.
4. Highest VI of mineral oils is about 115 and with special additives, this may be raised to about 160.
5. Hydraulic oils, used in remote control hydraulic circuits must have very high VI; otherwise erratic response to the controls can be troublesome. (Telemotor hydraulic system oil has VI of 110.)

Pour Point:

  • Lowest temperature at which an oil will barely flow.
  • Pour point indicates that oil is suitable for cold weather or not.
  • or crankcase oil, Pour Point is, – 18°C.

TAN and TBN:
1. TAN is the ability of an oil, to react with basic reagent, which indicates the acidity
expressed as TAN.
2. TBN is the ability of an oil, to react with acidic reagent, which gives an Alkali figure, the TBN.
3. Expressed in milligrams of KOH required to neutralise one gram of sample oil, for both TAN and TBN.
4. For crosshead type engine crankcase oil: TBN is 8 mg KOH/gm of oil.
5. For Trunk type engine using HO, crankcase oil: TBN is 30 mg KOH/gm of oil.

Detergency/Dispersancy:
1. Deposits occur in engine crankcase or ring zone, due to semi-solid precipitation from LO.
2. High temperature effect accelerates the rate of such deposition.
3. To reduce formation of such deposits, oil is treated with Detergent/Dispersant Additives, for keeping the system clean and trouble-free.
4. When using conventional mineral oils, these deposits block exhaust passage and prevent free movement of piston rings.
5. Addition of Detergent Additive prevents deposition of such deposits and washes them away with LO.
6. By addition of Dispersant Additive, tiny particles are carried in colloidal suspension, and dispersed evenly throughout the bulk of oil.
7. Detergent/Dispersant Additives are complex chemical compounds, such as metallic based Sulphonates, Phosphonates, Phenates and Salicylates.

Function of Lubricant:

1. Reduce friction.
2. Remove heat.
3. Flush away contaminants.
4. Protect corrosion.
5. Dampen noise.
6. In some case, act as sealant.

Types of Lubrication:

1. Hydrodynamic lubrication.
2. Boundary lubrication.
3. Hydrostatic lubrication.
4. Elasto hydrodynamic lubrication.

Hydrodynamic lubrication: 
1. Moving surfaces are completely separated by continuous unbroken film.
2. Lubricant, because of its viscosity, is drawn between the surfaces and builds up a film, by the action of moving parts.
3. Thickness of film: 0.025 – 0.10 mm.
4. Essential requirement is formation of oil wedge between the surfaces.
5. Lubrication for Journal Bearing, Bottom End Bearing, Tilting Pad Thrust Bearing.

Boundary lubrication.
1. It exists when full fluid film lubrication is not possible.
2. High friction between surfaces, and a degree of metal to metal contact occurs.
3. Lubricant oil film decreases, until asperities of mating surfaces touch.

Hydrostatic lubrication:
1. A form of Hydrodynamic lubrication, but instead of being self-generated, it is supplied from external source of oil under pressure, from a pump.
2. Lubrication for Crosshead Bearings, with attached pump.

Elasto-hydrodynamic lubrication:
1. Applied to line contact or nominal point between rolling or sliding surfaces, as in ball bearings, roller bearings and gear trains.
2. Thin film lubrication limits metal to metal contact.
3. Elastic deformation of metals occurs, and there is high-pressure effect on the lubricant.

Contaminants in LO:

(1) Water:
1. Owing to condensation of water vapour in crankcase.
2. Leakage from cooling water system for cylinder or piston.
3. Combined with oil in the form of emulsion.
4. Combined with sulphurous products of combustion to form Sulphuric Acid, in trunk engine.

(2) Fuel Dilution:
1. Presence of fuel oil in crankcase oil is indicated by reduction in viscosity and flash point.
2. Result from poor atomisation of fuel injectors.

(3) Oxidation Products:
1. Mineral oils react with oxygen in air and form oil-soluble organic acid, lacquers, resin and sludge, depending upon temperature and degree of contact with air.
2. Accelerated by contact with copper and iron, which act as catalyst.

(4) Fuel Combustion Products:
1. Mainly acids and incompletely burnt fuel form sludge and deposits.
2. Inorganic acids from combustion of high-sulphur residual fuel.

(5) Foreign Mineral Matters:
1. Rust and scales from storage tanks and pipes, etc.
2. Dust from surrounding atmosphere.
3. Wear debris from lubricated surface [not entirely hydrodynamic], and from corrosion of cylinder liner.

(6) Biological contamination:
1. Associated with ‘wet oil’ caused by leakage from cooling system.
2. It causes formation of organic acids, sludge and additive depletion, corrosion of shaft and bearings.
3. If happened, complete oil change may be necessary, thorough sterilisation and cleaning out of cooling system, and leakage to be stopped.
4. Addition of biocides to both oil and water, helps.

Symptoms of LO Contamination:

1. Increased Sump sounding (severe SW contamination).
2. Change in pressure and colour (Emulsification of oil, with water and residues of treated cylinder oil from diaphragm or scrapper box leakage).
3. Change in pressure (Reduction in viscosity and flash point, due to fuel oils.)
4. Frequent choking of filters due to sludge formation and Additive depletion, due to biological contamination.
5. Darkened oil colour and yellowish colour film on surface, pungent smell & sludge formation, due to microbial degradation.
6. Particles of rust and scales, mostly ferrous, trapped in magnetic filter (Corrosion of shaft and bearings, due to water, fuel combustion products.)
7. Wear debris, and welding spatter trapped at magnetic filter (Contamination of foreign mineral matters.

How to remove contaminants:
1. Filtering – removed large oil insoluble matter.
2. Gravity separation – heavy matters, sludge and water.
3. Adding special additives – reduce acids, sludge, finer oil insoluble matter.
4. Centrifuging – Sludge, foreign matter and water.
5. Water washing – only for straight mineral oil or oil without additives, can remove acids.

Water washing:
1. It can be carried out on straight mineral oil but not for detergent / dispersant type oil
2. The purpose is to remove acids, salts and other impurities from the oil.
3. Water should be injected before purification at a rate of 3% to 5% of oil flow.
4. Oil temperature should be around 75˙C and water temperature about 5˙C higher than oil temperature.

Batch purification:
1. If oil is contaminated with strong acids, high insoluble contents or water, batch purification of the entire charge oil should be done.
2. In port, the entire charge oil is pumped by purifier or circulating pump into Renovating Tank, fitted with steam heating coils.
3. Allowed to settle for at least 24 hours at about 60˙C.
4. Water and sludge must be periodically drained out.
5. Then oil is passed through the purifier at its optimum throughput and pumped back to Sump Tank.
6. During the time when the sump tank is empty, its interior should be cleaned and examined.
7. This should be done at least once a year.

Throughput of a purifier: The best purification result is obtained if oil is kept inside the bowl as long as possible, i.e. throughput should be as low as possible and also more frequent desludging once every hour.

If LO is contaminated with SW:

1. When sump oil is contaminated with SW, find sources of leakage [may be from LO cooler during ME stoppage] and rectified.
2. In port or while ME is stopped, transfer contaminated oil through purifier or transfer pump into Renovating Tank, settled for at least 24 hours at about 60°C, and water and sludge drained out periodically.
3. Oil passed through purifier at 78°C with optimum efficiency, and pump back to Renovating Tank.
4. When Sump Tank is empty, interior cleaned and examined.
5. Purified oil sent to Laboratory and tested.
6. During this time, new oil should be used.
7. Oil should be reused, if Lab results recommended that it is fit for further use.
[Straight mineral oil: 3% water washed. Additive oil: 1% water washed.]

L.O. for Crankcase Viscosity 130 – 240 Sec. Redwood No. 1 at 60’C.
VI 75 – 85 Pour pt. – 18’C Closed flash pt.220’C
TBN (trunk type) 30 mgKOH/gm of oil
TBN ( X-Head Type ) 8 mgKOH/gm of oil.

Water in LO
Effects:
1. Can form Acids.
2. Can cause corrosion on m/c parts.
3. Microbial degradation. [Reduce centrifuging efficiency; promote local pitting and corrosion].
4. Reduce load carrying capacity.
5. Reduce L.O. properties, and TBN of oil.
6. Form sludge due to emulsification.
Remedies:
1. Proper purification with minimum throughput.
2. Batch purification if heavy contamination.

Maximum Allowable % of water in LO
1. For crosshead engine, < 0.2% is satisfactory. 2. If water content exceed 0.5 ~ 1.0%, immediate action should be taken. If > 1%, engine can be damaged.
3. For trunk type engine, < 0.1% is satisfactory. If > 0.5%, immediate action should be taken and
it is maximum permissible content.

LO tests onboard:

Tests carried out on used diesel crankcase oil:
1. Viscosity {changes caused by dilution with fuel oil}.
2. Closed flash point {changes caused by dilution with fuel oil}.
3. Insoluble
4. Water content
5. Acidity.

(1) Viscosity determination:
–  Viscosity and closed flash point will fall by fuel oil contamination.
–  Changes in these values are a measure of dilution, and up to 8% contamination can be tolerated.
Three Tubes Rolling Ball Viscometer:
1. Assume that system oil is SAE 30.
2. One tube filled with minimum safe viscosity, SAE 20.
3. One tube filled with maximum safe viscosity, SAE 40.
4. Last tube filled with test sample.
5. All tubes placed in warm water, until at same temperature.
6. All tubes placed on tilted board and inverted, so that internal hollow balls rise to surface, with different time taken.
7. If time taken for test sample is between upper and lower limit oils, this sample oil is fit for further use.

(2) Insoluble Content:
» Insoluble are soot, dust, metallic particles, asphaltene, oxidation products, and products of deterioration.
Blotter Test:
1. Single drop of sample oil is released from a given height onto a sheet of Special Filter Paper.
2. The result is compared with Standard Test Paper, of similar oil with known varying insoluble content.
3. Test oil should be below the upper limit:
Upper limits of insoluble are: 1.00% to 1.5% for Straight Mineral Oil,
5% for Detergent/Dispersant type Oil.
(3) Water and other contaminants by:

Crackle Test:
1. Pour a known amount of sample oil into a test tube.
2. Hold the test tube over small spirit lamp, shaking it while doing so.
3. If there is no crackling, the oil is dry.
A slight crackle indicates a trace of water.

(4) Acidity Determination:

1. Tested by extracting the acids from sample oil, by means of shaking with known amount of distilled water, in a test tube.
2. Acidic extract is placed on a watch glass, with Indicator Solution of known strength.
3. The mixture is drawn into a glass tube, and compared with Colour Standards, each representing a known pH value. Sample can be determined quite accurately.

Microbial Degradation:

  • If free water is present in crankcase, micro-organisms may grow, at oil water interface, by consuming hydrocarbons in oil.
  • Infestation at early stage may not be harmful but in case of severe infestation, corrosion within machinery parts may arise.
  • Complete oil change is necessary.

Indication:

1) Darkened oil colour and yellowish colour film on surface.
2) Pungent smell
3) Sludge formation.

Poor quality fuel:

High pour point.: Needs extra heating for storage tank.
High density: Causes purification difficulties.
High viscosity: Pumping difficulties and more heat required getting suitable injection
viscosity at injector.
Low cetane number. Late injection and after burning. It is considered as poor fuel, if C  37 .
Abrasive group: (ash, silica, nickel, catfines): Cause wear on cylinder liner, piston rings, ring
grooves and fuel injection equipment.
Corrosion group: (Sulphur, Vanadium, Sodium): Low temperature corrosion due to sulphur.
Acid dew point is 120 – 160°C
High temperature corrosion due to Vanadium, Sodium and Sulphur
at 460 – 570°C
Corrosion or vapour locking at fuel injection equipment, due to water.
Fouling group: (catfines, CCR): Slow burning due to Asphaltine, combustion space fouling
and T/C fouling due to CCR.

Flash Point:
1. Lowest temperature at which an oil will give off sufficient flammable vapour, to produce a flash when a small flame is brought to the surface of the oil.
2. Minimum flash point for on-board use is 60°C.
3. Fuel storage temperature must be kept at least 14°C lower than its flash point.
4. Average closed flash points: Petrol – 20°C: Paraffin 40°C: Diesel Oil 65°C:
LO 220°C: 70 cst Fuel Oil 71°C: Heavy Oil 100°C:

Pour Point:
1. Lowest temperature at which the oil barely flow.
2. It is just above the lowest temperature at which liquid flows under its own weight.
3. It must be low, otherwise fuel tends to solidify and due to poor heat transfer property, fuel cannot be returned to its original state by heating.
4. Fuel storage temperature must be kept at least 10°C higher than its pour point.
5. At least 40 – 50°C higher than its pour point, for cold weather condition.

Homogenizer:
1. It is a device to create stable oil and water emulsion, which can be bunt in boilers and diesel engines.
2. This emulsion can burn more efficiently and reduce solid emission in exhaust gas.
3. It can reduce catfines into finely ground particles, which do not harm.

Bunkering Operation

How to order bunker:

1. Take essential data from master, such as distance to go with average speed, river passage, pilotage, port stay, etc. To check ROB.
2. Estimate HO and DO consumption based on weather, wind and current condition, running hours of AEs auxiliary boiler and ME.
3. Estimate the 3 days reserve, considering unpumpable quantity, bunker allowance or bunker margin.
4. Calculate the capacity to receive, bunker amount, type of bunker, HO, DO or LO.
5. Bunker should be allowed 85% of tank capacity.
6. Arrange not to mix with remaining onboard fuel.

Total required bunker from port to port = {Distance to go with average speed + River
Passage + Pilotage + Port Stay + 3 Days Reserve }

Bunker to be ordered: = { Total required – ROB }

CE’s Responsibility during Bunkering:
CE is overall in charge of bunkering.

Responsibilities are:

1. Fire prevention
2. Oil pollution prevention
3. Calculation
4. Recording and informing.

Discuss at Bunkering Meeting about: Quantity / Bunkering Sequence / Distribution Plan.
Make preparations for both Deck and Engine Department, in accordance with pre-bunkering checklist.
Prepare all necessary papers as per local regulations.

Fire Prevention:

1. Prohibit naked light and smoking around bunker area.
2. Place portable fire extinguisher at bunker point.
3. Bunker oil flash point ≮ 65°C, as a rule.
4. Ensure no oil leakage.

Pollution Prevention:

1. Clear overflow tank and top up settling and service tank.
2. Clean System filters, sight glass, and pressure gauge in good order.
3. Ensure bunker system valves in good order, and the correct valves have been opened.
4. Take all soundings of fuel tanks, and calculate the amount to be put into each tank.
( 85% of tank capacity is maximum. )
5. Explain bunkering sequence to all engineers.
6. Check security of hose coupling, and one responsible engineer to be stand-by at bunker station to watch break or spill at hose connection.
7. Agree the pumping rate or pressure with pump man or barge master, remembering that a burst hose can cause pollution. Discuss slow down operation and emergency stop procedure.
8. Make good communication between bunker point, barge or shore supply, and tank control station.
9. Leakage or overflow of oil to deck strictly prevented. Saw dust, OSD, and rags, ready at bunker point.
10. Duty officer to be informed, the amount to be bunkered and expected time of the work.
11. Plugged all deck scuppers.
12. Maintain the upright position as possible as.

 

For Calculations:

1. Take all soundings of fuel tanks, before and after bunkering.
2. Take fore and aft draughts, before and after bunkering.
3. Take soundings of barge or to check flow meter reading, before and after bunkering.
4. Record the oil temperature.
5. Calculate corrected sp.gr. at measuring point temperature, SGc.
6. By multiplying SGc with total volume, obtained from sounding table, total amount of bunker in tons will be obtained.

Bunker Barge Arrival:

1. Record exact time of barge arrival and departure.
2. Check local supplier’s paperwork, to ensure that specification and quantity ordered is correct.
3. Check for correct specification, and compatibility tested, by using a test kit.
4. Check water content of bunker is at acceptable level.
5. Ensure that onboard fuel handling equipment is adequate and serviceable at all times.

Bunkering:

1. Start bunkering at slow rate, and then raise the pumping rate.
2. Always check and witness the flow meters, tank gauges and tank dips, before and after delivery, to ensure that the right quantity has in fact been supplied.
3. Random checks to ensure correct specification of oil being supplied during bunkering.
4. Take a continuous drip sample. Compatibility test of bunker carried out.
5. Always insist on being given a sealed sample of bunkers delivered, which should be witnessed and signed by both parties.
6. When 80% of total capacity reaches, pumping rate slow down and final topping up done.

After Bunkering:

1. Record the time and read flow meter on bunker boat or on shore.
2. All filling valves kept open, until final air blowing is completed.
3. Remain hose connections until correct quantity of oil has been received after calculation.
4. Then close bunker main valve, system valves and individual tank valves.
5. Take final soundings and bunker temperature from both ship and barge to calculate actual amount.
6. When calculating the bunker received, the ship’s trim and temperature of the oil must be taken into account.
7. Both party signed on sample bottles and sent to laboratory. The statutory sample to be kept in sample store and retain it for 12month.
8. Inform duty officer, starting and stopping time, amount of bunker received and tank soundings, for stability calculation and custom claiming purposes.
9. Make entries into ORB, Sulphur record book and Logbook.
10. BDN to be collected from supplier and file it properly to retain it for 3 years.
10. Prepare Bunker Report and sent to HO.

FO Overflow while Bunkering: [Action taken by CE.]

1. Stop pumping of fuel immediately.
2. Report to Master and contact Port Authority or persons concerned, about oil pollution incident.
3. Detail description of actions taken immediately by crew, using equipment from Oil Spill Locker to reduce and control the oil flow.
4. Arrange point of contact onboard, for co-ordinating shipboard action with local authorities, in combating pollution.
5. Make entry into ORB, date, time, place and amount of overflow.

Bad fuel:

1. Bunker should be received in empty tank and made segregated.
2. During bunkering, compatibility test should be done.
3. Sealed sample sent to laboratory for analysis.
4. Maintain storage temperature well above pour point. (About 40’/50’C under coldest climate condition.)
5. Settling tank temperature maintained about 14’C below flash point to improve gravitational separation. Regular drain out of water and impurities.
6. Fuel transfer lines steam traced, and transfer pump suction filter cleaned.
7. If necessary, dose chemicals, e.g. Gamma Break- Unitor, into storage tanks ( DB tanks) by using dosage pump for chemical.
8. Regular cleaning of coarse filters.
9. Two purifiers run in parallel, to get enough fuel for engine, with optimum throughput and correct heating temperature (98’C). Gravity disc, carefully chosen. If necessary, double stage centrifuging will be done with purification and clarification in series.
10. Maintain correct service tank temperature. Dose some chemicals, to improve combustion efficiency. (Duel Purpose Plus, Unitor)
11. Maintain correct oil temperature, to get suitable viscosity at injectors,
( 10 ~ 18 Cst.). Fuel outlet from heater, controlled by Viscotherm Unit.
12. Steam tracer lines correctly heated, up to injector.
13. Maintain correct working temperature of engine, to prevent hot and cold corrosion due to Vanadium and Sulphur attacks.
14. Check engine performance by taking indicator diagram.
15. If damage occurred due to bad fuel, prepare for insurance claim.

Compatibility:
1. Ability of two fuel to be blended together without precipitation of sediments, such as asphaltine and sludge, etc.
2. Due to asphaltine and sludge, it can cause choking of filters, overloading of purifier and immobilisation of vessel in severe case.

Remedies: For Incompatibility:
1. Keep fuels in empty tank and segregated.
2. Always carry out compatibility test when bunkering.
3. Incorporate homogenisation system to completely mix incompatible fuel components prior to injectors.

Compatibility Test:
1. Pour 40 ml of sample into test tube. (20 ml for each fuel)
2. Add reagent of white spirit up to 80 ml. (ē 40 ml white sprit)
3. Then the mixture is mixed well.
4. One drop of mixture is deposited on chromatographic paper and allowed to dry at room temperature.
5. Then test drop is compared with five standard spots.
Spot 1 ~ 2 indicate compatible fuel.
Spot 3 ~ 5 indicate incompatible fuel.

Requirements for the use of high viscosity fuel:

1. Bunker tank-heating systems capable of maintaining fuel temperature about
40-50’C higher than Pour Point under the coldest climate condition.
2. Exposed bunker transfer pipes insulated and trace heated.
3. Treatment plant capable of purifying/clarifying high density fuels.
4. Engine preheaters designed to achieve recommended injection viscosity.
5. Trace heated and pressurised engine fuel system, allowing manoeuvring on residual fuel.
6. Main and auxiliary engine designed to burn high viscosity fuel oil.

Effects of Bad Fuel Oil:

1. Too much sludge formation in DB tank.
2. Frequent fuel line filter blockage.
3. Upsetting purifier.
4. Premature wears of fuel pump.
5. Carbon trumpet formation and leaky FV.
6. Excessive wears and cold corrosion of cylinder liner.
7. Excessive carbon deposits in piston rings.
8. Hot corrosion attack on Exhaust valve.
9. Choked turbine nozzle rings and broken blades.
10. Excessive carbon deposits on EGE.

Bunker Specifications:
Includes: Name of vessel, Port of bunker, Date of delivery, Product name, Temperature of product, Sulphur Content,
Quality:
1. SG at 15°C
2. Viscosity at 50°C
3. Sulphur content % by weight
4. CCR % by weight
5. Flash Point [closed] °C
6. Pour Point °C
7. Water content % by volume
8. Sludge / Sediment % by weight
9. Cetane No.
10. Vanadium in ppm.

Bunkering:
1. Slow rate and record.
2. Take soundings.
3. Random check
4. Continuous drip sample.
5. Compatibility test
6. Slow down when 80% is reached.
7. Remain v/vs opened until after air blow.
8. Remain hose connection until after calculation.
9. Take sealed sample
10. Close all valves.

Viscotherm Unit:
A device to adjust the viscosity of oil to get desired value, which is essential for correct atomisation and combustion of engine.

Operation:
1. Constant quantity of oil is taken from the flow and fed into capillary tube by means of motor operated gear pump through reduction gear.
2. Oil flows through capillary tube under laminar condition and pressure drop across the tube is measured by DP cell and its signal is directly proportional to oil viscosity. A transducer is incorporated with DP cell.
3. Signal given by DP cell is compared with a set value and any deviation can cause
drive signal to adjust pneumatic control steam inlet valve to oil heater.
4. Normally the required injection viscosity is 10 ~ 18 Centistrokes and required value is set at transducer.

VIT:

1. Load-dependent start of fuel injection control system.
2. VIT mechanism automatically change the fuel injection timing, according to load,
to get maximum combustion pressure (Pmax) at engine load between 85% ~ 100%.
3. Reduction in SFOC is about 2.0 gm / bhp / hr at 85% engine load.
4. VIT fuel pump incorporates variable injection timing with optimised fuel economy,
at part load.
5. Expansion Ratio is increased.
Maximum Pressure
Expansion Ratio =
Pressure at the start of Exhaust Blow-down

6. Required fuel viscosity at engine inlet is 10 ~ 20 Cst.

In other words:
1. If an engine running at prolong period at reduced load, lower air temperature after compression, will cause increase in ignition delay of injected fuel, subsequently causing knocks and poor combustion.
2. This problem can be reduced by adoption of VIT system, to advance the start of injection, then allowing the same Pmax, at part load.

Operation of VIT: [ Valve control type: Sulzer RTA ]

1. Fuel Quality Setting [FQS] lever is used for manual adjustment of VIT mechanism to alter valves timing, according to ignition quality of fuel used. [If poorer quality fuel is used at same valve timing, Pmax will drop, and with better ignition quality fuel, Pmax will rise.]
2. VIT mechanism is linked to Governor Load Setting Shaft and built-in cam system, which is positioned by FQS lever.
3. This mechanism controls the timings of Suction Valve closure (beginning of delivery) and Spill Valve opening (end of delivery) through linkages simultaneously.
4. Hence, fuel injection timing, Pmax, and fuel delivery to injectors, are controlled load-dependently.

Thermal Cracking:

1. Atoms within hydrocarbon molecule are excited by heating, thus lighter fraction of molecule breaks-off and condensed.
2. Remaining portions of original molecule then unite to form more heavier molecule.
3. Thermal cracking produces Asphaltene, which has heavy hydrocarbon molecules,
causing slow burning in fuel combustion.

Written by Marine Study

Marine Study

“For Maritime Education and Knowledge”

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