MARINE LUBRICATION

INTRODUCTION

Lubricating oil for a marine diesel engine achieves two objectives; it must cool and lubricate.

The oil is taken from the drain tank usually underneath the engine by a screw type pump. It is cooled, filtered and
supplied to the engine via the oil inlet pipe or inlet rail at a pressure of about 4 bar. On a medium speed 4 stroke engine
the oil is supplied to the main bearings through drillings in the engine frame to the crankshaft main bearings. Drillings in
the crankshaft then take the oil to the crankpin or bottom end bearings. The oil is then led up the connecting rod to the
piston or gudgeon pin and from there to the piston cooling before returning to the crankcase.

Oil is also supplied to lubricate the rocker gear operating the inlet and exhaust valves, and to the camshaft and camshaft drive.

The oil then drains from the crankcase into the drain tank or sump.

The oil in the drain tank is being constantly circulated through a centrifugal purifier. This is to remove any water and products of
combustion plus any foreign particles which may be in the oil.

The cylinder liner must be lubricated as well. This is so there will be a film of oil between the piston rings and the liner and also so that
any acid produced by combustion of the fuel is neutralised by the oil and does not cause corrosion. Some of this lubrication will be
supplied by so called "splash lubrication" which is the oil splashed up into the liner by the rotating crankshaft. However larger medium
speed marine diesel engines also use separate pumps to supply oil under pressure to the cylinder liner. The oil is led through drillings
onto the liner surface where grooves distribute it circumferentially around the liner, and the piston rings spread it up and down the
surface of the liner.

A pre-lub pump is sometimes fitted especially to engines where the main pump is engine driven. This pump is electrically driven and
circulates oil around the engine prior to starting.
 On a two stroke crosshead engine lubricating oil is supplied to the main bearings and
camshaft and camshaft drive. A separate supply is led via a swinging arm or a telescopic pipe to the crosshead where some of it is
diverted to cool the piston (travelling up and back through the piston rod), whilst some is used to lubricate the crosshead and guides,
and the rest led down a drilling in the connecting rod to the bottom end or crankpin bearing. Oil is also used to operate the hydraulic
exhaust valves.

On some engines, the oil supply to the crosshead bearing is boosted in pressure to about 12 bar by a second set of pumps. This oil is
also used to operate the hydraulic reversing gear for the engine.

The cylinder liners on a two stroke engine are lubricated using separate injection pumps which use a different specification of oil. The
oil which is led to drillings in the liner is able to deal with the acids produced by the burning of high sulphur fuels.

Oil grooves in a cylinder liner

 Cylinder Lubricators

Lubricating oil system for a marine diesel engine - how it works

Lubricating oil system

Lubricating oil for an engine is stored in the bottom of the crankcase, known as the sump, or in a drain tank located
beneath the engine. The oil is drawn from this tank through a strainer, one of a pair of pumps, into one of a pair of fine
filters. It is then passed through a cooler before entering the engine and being distributed to the various branch pipes.

The branch pipe for a particular cylinder may feed the main bearing, for instance. Some of this oil will pass along a drilled
passage in the crankshaft to the bottom end bearing and then up a drilled passage in the connecting rod to the gudgeon
pin or crosshead bearing.

An alarm at the end of the distribution pipe ensures that adequate pressure is maintained by the pump. Pumps and fine
filters are arranged in duplicate with one as standby. The fine filters will be arranged so that one can be cleaned while
the other is operating. After use in the engine the lubricating oil drains back to the sump or drain tank for re-use. A level
gauge gives a local read-out of the drain tank contents. A centrifuge is arranged for cleaning the lubricating oil in the
system and clean oil can be provided from a storage tank.

The oil cooler is circulated by sea water, which is at a lower pressure than the oil. As a result any leak in the cooler will
mean a loss of oil and not contamination of the oil by sea water.
Where the engine has oil-cooled pistons they will be supplied from the lubricating oil system, possibly at a higher
pressure produced by booster pumps. An appropriate type of lubricating oil must be used for oil-lubricated pistons in
order to avoid carbon deposits on the hotter parts of the system.

Cylinder lubrication
Large slow-speed diesel engines are provided with a separate lubrication system for the cylinder liners. Oil is injected
between the liner and the piston by mechanical lubricators which supply their individual cylinder, A special type of oil is
used which is not recovered. As well as lubricating, it assists in forming a gas seal and contains additives which clean the
cylinder liner.

Lubricating Oil Sump Level

The level of lubricating oil indicated in the sump when the main engine is running must be sufficient to prevent vortexing
and ingress of air which can lead to bearing damage.
The sump level is to be according to manufacturers/shipbuilders instructions . The ‘Sump Quantity’ is always maintained
at the same safe operating level and is given in litres. It is essential that the figures are mathematically steady and
correct from month-to-month, taking into account consumption, losses and refills and reported .

The ‘Sump Quantity’ is calculated with the engine stopped, but the lubricating oil pump in operation, thus keeping the
system oil in circulation.
Sufficient reserve quantities of lubricating oil must always be held, i.e. to completely fill the main sump and sufficient
quantities of other lubes must be held to cover the intended voyage plus 20%. Lubricating oils are a major expenditure
item, therefore, all purchasing must be pre-planned with the aim of buying the maximum amounts from the cheapest
supply sources which are primarily the US, Europe and Singapore. Lub oil requisitions should be sent to the office at least
10 days before the intended port of purchase and clearly indicate if the vessel requires supply in bulk or in drums.

Pre-Lubrication Pumps

They provide an essential part of the lubrication system on many types of engine in particular auxiliary engines with
engine driven lubricating oil pumps.
They provide a supply of oil to the bearings prior to start up and limit the length of time that boundary lubrication exists,
and shorten the time when hydrodynamic lubrication commences. They must be maintained and operated in
accordance with the manufacturers’ instructions.

Why lubricating oil cooler is installed after lube oil filter ?

 It is more effective to filter the hot oil, as pressure drop through the filter is less and filter is more efficient.

Important Lube Oil Properties to be Considered While Choosing Marine Lube Oil for Your Ship
Lube oil is a one of the essential elements for operating any kind of machinery on board ship. Lube oil is responsible for
lubrication and cooling of the parts which are operating relative to each other, giving rise to frictional and other types of
stresses on the machinery. Without the use of lube oil, we cannot imagine any machinery operation on ship.

Different types and grades of lube oils are available for machinery, depending upon the working condition, operation,
and requirements of the machinery itself. When it comes to marine engines, it is very critical to select the best grade of
lube oil that can be used as crank case oil or cylinder oil. The lube oil is selected based on the properties which will
improve the engine operation and reduce the wear down rate and hence the maintenance cost of the machine.

Functions and Properties of Lubricating oil on Ships

What are the functions of a lubricant?

1. Separate entirely the contact surfaces, thereby reducing static and dynamic friction to least possible value to
prevent wear and tear.

2. Remove heat generated within the bearing.

3. Protection of the working surfaces against corrosion.

4. Removal of contaminants.

5. Dampen noise produced.

6. Act as a sealant.

What are the Types of Lubrication on Ships?

 Hydrodynamic Lubrication or Full fluid film lubrication.

 Boundary Lubrication or Thin film lubrication.

 Hydrostatic Lubrication or Thick film lubrication.

 Elasto-hydrodynamic Lubrication or Thin film or square film lubrication.

The following are the most common and required properties of the lube oil used for marine machinery:

Alkalinity

The lube oil alkalinity plays an important part in marine engines. When fuel burns, the fumes carry sulphuric acid which
can cause acidic corrosion. For a trunk piston engine or four stroke engines, the main lube oil is responsible
for piston and liner lubrication; hence it comes directly in contact with the combustible fuel. Therefore alkalinity of lube
oil is important for controlling acidic corrosion.
For two stroke engines, separate grade of lube oil is used as cylinder oil and its alkalinity depends on the engine fuel
grade (HFO or LSFO).

Oxidation resistant

Lube oil is always in contact with air and thus oxygen presence in oil is inevitable. Moreover, at high temperature of the
oil, the oxidation rate increases. After 85̊ degree C temperature, the increase in every 10̊ degree C of oil oxidation rates
doubles itself leading to sludge formation, acid production and bearing corrosion. Hence additives are added to maintain
keep these things in check. Lube oil temperature is controlled by passing it through lube oil cooler.

Load carrying capacity

It is also one of the important characteristics of lube oil which mainly depends upon the viscosity of the oil. The load
subjected to different internal parts of the marine engine is very high; hence the load carrying capacity must be enough
to withstand the pressure inside the engine. If this is not achieved then oil will be forced out and metal to metal contact
will result in wiping out and wear down of the machine.

Thermal conductivity

The internal parts of marine engine are always in movement producing heat energy. This heat energy has to be carried
away or else it might lead to wear down due to thermal stresses. The lube oil must cool down the internal parts to avoid
such a situation and must have a good thermal conductivity.

Detergency

Detergency of the oil is obtained by adding some metallic based additives which will prevent the build up of small
deposits in the metal surface. In two stroke engine, the cylinder oil detergency is very important as it removes the
deposits from the ring pack area and keeps the combustion space as clean as possible

Disperency

It is the property of the lube oil which prevents impurities to mix up with itself and keeps them suspended on the
surface. This makes it easy for the separator or clarifier to remove it from the oil.

High Flash Point

The flash point is the minimum temperature at which the oil vaporizes to give an ignitable mixture of air. The flash point
should always be on the higher side so that in case of increase in temperature of the oil, fire hazard can be avoided.
Normally for marine engine lube oils, the flash point is always higher than 220̊ C.

Low Demulsification Number

It is not practically impossible to completely avoid contamination of oil with water. The low demulsification number of
the oil helps in easy separation of water from the oil in the separator or when stored in the settling tank.

What are the Properties of crankcase lubricating oil?

  Viscosity: To be suitable for the purpose

 Viscosity index: To be high

 Pour Point: Must be low

 Flash point: Must be high

 Oxidation stability: To be high

 Carbon residues: To be low

 Total acid number or TAN: To be suitable for the purpose

 Total basic number or TBN: To be suitable for the purpose

 Detergency: For cleaning

 Dispersancy: To facilitate purification

What are the contaminants in the lube oil?

1. Contamination of fresh Water (JW leaking)

2. Contamination of Sea Water (Cooler leakage)

3. Contamination of fuel (Poor Atomisation, Unburned Fuel)

4. Oxidation products (High Exhaust Temperature, Burned Cyl Oil, Carbon from incomplete combustion)

5. Products of fuel combustion

6. Foreign mineral matters (Scale formation, Wear and tear)

7. Biological contamination.

What are the effects of water contamination in lube oil?

Causes

1. Condensation of water vapour within the crankcase

2. Leakage from the cooling water system for cylinder or piston

3. Leakage from the sump tank heating steam coils.

Effects

1. Reduce cooling efficiency.

 2. Increase the acid formation in trunk type piston engine.

3. Can cause corrosion on machine parts.

4. Microbial degradation, [Reduce centrifuging efficiency; promote local pitting and corrosion]

5. Reduce load carrying capacity

6. Reduce Lube Oil properties, and TBN of oil

7. Form sludge due to emulsification

Remedies

1. Proper purification with minimum throughput

2. Batch purification if heavy contamination

What is meant by batch purification?

1. Firstly take the immobilization permit from the port authority.

2. The entire oil charge should be pumped by the purifier or by main circulation p/p into settling tank.

3. It should be allowed to settle for at least for 24 hours with heating about 60° C .

4. Water and sludge should be drained out periodically.

5. Cleaned the interior of the sump tank and carefully examined.

6. The oil should be passed through the purifier at its optimum efficiency and then pump back into the sump tank.

When sump tank empty, its interior should be cleaned and examined.

Maximum Allowable Amount of water in Lube oil?

 For crosshead type engine , < 0.2 % is satisfactory

 If water content exceed 0.5 ~ 1.0 %, immediate action should be taken

 If > 1%, engine can be damaged

 For trunk type engine , < 0.1% is satisfactory

 If > 0.5 %, immediate action should be taken and

 It is maximum permissible content

What are the effects of fuel dilution in lube oil?

Causes

1. Poor atomization of a fuel injector and back leak through the fuel injector p/p plunger and barrel.

Effects

1. Fuel dilution usually diesel oil.

2. Lower viscosity and low fresh point

3. Lower viscosity Lube Oil reduces this properties ( e.g load carrying capacity )

4. Lower fresh point will cause crankcase explosion.

How to remove contaminants

1. Filtering: Removes large oil insoluble matter

2. Gravity separation: Removes heavy matters, sludge and water

3. Adding special additives: Reduce acids, sludge, finer oil insoluble matter

4. Centrifuging: Removes sludge, foreign matter and water

5. Water washing: Only for straight mineral oil or oil without additives, can remove acids.

What will you do if Lube Oil is contaminated with Fresh Water or Sea Water?

1. Batch Purification must be done

2. Renovating Tank heating and regular draining

3. For Sea Water contamination, Water Washing is required

4. Sump to be opened and thoroughly wipe out.

How to maintain lube oil on board ships?

1. Lube Oil onboard test is carried out regularly.

2. Regular cleaned Lube Oil line filter.

3. Lube Oil purifier should be run during ship is in sea

4. Maintain Lube Oil purifier performance

5. Periodic batch purification must be carried out & cleaned Lube Oil sump tank once a year

6. Maintain Lube Oil temperature within limit.

 7. Maintain good Lube Oil cooler efficiency

8. Keep good fuel combustion system

What are the lube oil tests carried out on board Ships?

Viscosity Determination

 The simplest method is three tube rolling ball viscometer

 Assuming the oil in the engine to be SAE 30 grade, one tube is filled with minimum safety viscosity (about SAE
20) and another one filled with maximum safety viscosity (about SAE 40). The last tube is to be filled with test
sample.

 All tubes are placed in a bucket of warm water until the oils are at the same temperature.

 The three tubes then mounted on a tilted board and inverted. An internal hollow ball in each tube then rises to
the surface.

 If the time taken in the test sample is between that of the lower and upper limit oils, the oil is fit for further use.
If not, it must be replaced.

Insoluble Content

 A drop of sample oil is released from a given height onto a special filter paper.

 Compare the result with the known varying insoluble content. The upper limit for straight mineral oil is 1% to 1.5
% and for detergent dispersant oil is 5%.

Water and other Contaminants

A known amount of sample oil in the test tube is heated and must be shaken the while doing so

 If there is no cracking, the oil is dry

 If there is slightly cracking, the oil having a trace of water

 If there is a heavily crackling, the oil is heavily diluted with water

Acidity / Alkalinity Determination

Acidity is tested by extracting the acids from the sample by means of shaking with a known amount of distilled water.
The acidic extract is then placed on a watch glass with an indicator solution of known strength. The mixture is then
drawn up into a glass tube and its colour compared with a series of colour standards, each representing a known PH
value, from which the sample can be determined quite accurately.

Another method is:

A drop of indicator solution is placed on to blotting paper and this is followed by a drop of sample oil placed at the
centre of the drop of previous absorbed indicator.

 If the change of colour is Red, it is acid.

 If blue/green, it is alkaline.

 If yellow/green, it is neutral.

Foreign Particles Test

 This can be done by either Spectrochemical analysis or Ferrographic analysis, each giving particle size less than
10 uM to 100 uM range depending on the tests applied.

 The most powerful technique is Inductively coupled plasma atomic emission spectrometry (ICP OR PES), which
uses a direct spray technique to determine the wear and contaminant elements present in the oil. This
technique will in the main only detect the particles below 10 uM size.

 In ferrographic test, the sample is thinned first with some solvents and allowed to pass slowly down a slide
surrounded by powerful magnetic field. Then it is examined by special microscope with red and green filters
under lights. The shape of the particles is used to identify the source of the wear debris.

 The advance ferrography method was added to the PFA (Progressive Fast Analysis) programme where all
samples pass through the combination of two machines, a particle quantifier (PQ) and a rotary particle depositor
(RPD). These test measures the induced magnetic moment of debris as deposited on a substrate or contained
within a specific volume of liquid.

 These machines provide accurate test by rotating the metal particles and then separating into three different
sizes, Theses three bands of particles are examined by very powerful microscope to determine the type of
materials and shape.

 If more detailed examination is necessary, the debris may be subjected to a scanning electron microscope.

ENGINE LUBRICATION

High speed engine oils

Marine high speed engine lubricants are high performance diesel engine oils that help extend engine life and protect
components at high temperatures.

MEDIUM SPEED ENGINES

Medium speed engine oils

Medium speed engine oil for use in heavy fuel oil engines helps to protect against deposits in the most severe marine
diesel applications.

SLOW SPEED ENGINES OIL

Slow-speed cylinder and system oils

Slow-speed cylinder and system oils offer high-performance lubrication and enhanced protection from mechanical wear,
as well as helping to mitigate cold corrosion.

DIFFERENCES BETWEEN TWO STROKE AND FOUR STROKE ENGINES

Difference between 2 Stroke vs 4 Stroke Engine

Today I am going to tell you about main difference between 2 strokes vs 4 stroke engines. We all heard about both of
these engines but few of us know the basic differences between them. Before discussing on this topic first you should
know about stroke. The stroke in an engine is the distance covered by the piston from top dead center to the bottom
dead center. In simple words, stroke is the distance of cylinder between piston moves. If a piston moves 2 times in the
cylinder, that means, engine is known as two stroke engine and if it moves 4 times in a four stroke engine. The
crankshaft rotates one time between 2 strokes.
The basic and main difference between two stroke and four stroke engine is that the crankshaft complete one
revolution in one power stroke in 2 stroke engine and complete 2 revolution in one power stroke in four stroke engine.
So the 2 stroke engine give high power compare to 4 stroke engine but the 4 stroke engine is more fuel efficient. There
are many other differences which are given below.
Difference between 2 Stroke vs 4 Stroke Engine

S. No. Two Stroke Engine Four Stroke Engine

1. It has one revolution of crankshaft within one power It has two revolution of crankshaft between one power strokes.
stroke.

2. It can generate high torque compare to 4 strokes It generates less torque due to 2 revolution of crankshaft
engine. between one power strokes.

3. It used port to inlet and outlet of fuel. It used valve to inlet and outlet.

4. 2 stroke engines require lighter flywheel compare to It requires heavy flywheel because it generates unbalance force
other engines because it generates more balanced due to two revolutions for one power stroke.
force due to one revolution for one power stroke.

The charge is partially burn and mix with the burn In four stroke engine charge is fully burn and does not mix with
gases during inlet. It is due to port mechanism. burn charge in ideal condition.
5.

6. Comparatively complicated lubrication.

 Easy lubrication due to lubrication oil mix with the
fuel.

7. More lubricating oil requires because some oil burns Comparatively less lubricating oil requires.
with fuel.

8. These engines give less thermal efficiency. These engines give more thermal efficiency.

9. It has high power to weight ratio compare to others. 4 stroke engines have less power to weight ratio.

10. It creates more noise. It is less noisy.

11. Two stroke engines are less efficient and generate Four stroke engines are more efficient and generate less
more smoke. smoke.

12. These engines are comparatively cheaper. These engines are expansive due to valve and lubrication
mechanism.

13. These engines are easy to manufacture. These engines are comparatively hard to manufacture.
14. These engines are generally lighter. These engines are comparatively heavier than 2 strokes due to
heavy flywheel and valve mechanism.

15. These are mostly used in ships, scooters etc. These engines mostly used in car, truck, and other automobiles.

16. Due to poor lubrication more wear and tear occurs Less wear and tear occurs.