Diesel Engine Lubrication and Lube Oil Contamination Control

Diesel Engine Lubrication And Lube Oil Contamination
Control
Prepared By
Md. Moynul Islam
Chemical Engineer
Expertise on Marine Fuels and Lubricants
Contact
Email : engineer@moynulislam.com
Mobile : +8801816449869
Web : www.moynulislam.com
Last Modified On: February 05, 2015A downloadable “pdf “ version is available on author’s website

Diesel Engine Lubrication And Lube Oil Contamination Control
Identify contamination
Identify wear and its possible sources
Deploy appropriate contamination control guards
Move your maintenance practices toward a more condition-based-approach

Introduction
Lubricating oil is imperative for the correct function of an engine. It forms a
separating oil film between adjacent moving parts to prevent their direct contact,
decrease friction-induced heat and reduce wear. Therefore it protects the engine.
One of the most important characteristics of lubricating oil is its viscosity. This has
to be high enough to maintain the lubricating oil film and low enough to enable the
flow of oil around the engine.
During engine operation the characteristics of the oil change. Soot particles
generated in the combustion process, contaminate the oil along with small metallic
particles caused by mechanical abrasion. These contaminants increase the viscosity
of the oil and as a result the oil can no longer completely carry out its protective
function. This leads to increased fuel consumption, a loss of engine performance
and increased wear or damage to engine components.
In order to exclude these risks, the lubricating oil has to be effectively treated. The
focus of the treatment is the maintenance of the oil quality and
protection of the engine which are two equally important requirements.

Friction and Purpose of Lubrication
To understand lubrication you have to understand friction and also about following
things.
how friction causes damage
How operating conditions can increase damage
How lubricants help to prevent damage
Reducing friction between moving parts is critical to increasing vehicle/equipment life.
Purpose of Lubrication:
Protect critical components
Provide reliable operation
Lower maintenance costs
Decrease downtime
Increase equipment life
Main Functions of Lubricants:
Reduces friction in engines
Controls friction in transmissions
Acts as a heat transfer agent
Inhibits corrosion and oxidation
Removes contaminants
Lessens the effect of temperature extremes on viscosity
Noise Reduction

Engine Parts Lubrication and Engine Oils
Functions of Engine Oils
 Provision of stable oil film between moving surfaces
 Provision of reliable engine operation in a wide temperature range
 Rust / Corrosion protection in engine components
 Cleaning the engine components from sludge
 Sealing Piston Ring- Cylinder Gap
 Prevention of Foaming
 Cooling the Engine Parts
 Piston Motion in Cylinder
 Crankshaft Rotation in Engine Bearings (Main Bearings and Big End Bearings)
 Piston Pin Rotation in the Bush of Small End of the Connecting Rod
 Camshaft Rotation in Camshaft Bearings
 Cams Sliding Over the Valves Rods
 Intermediate Gears
 Turbocharger Bearings
 Pedestal Bearing
 Reciprocating Motion of Valve Stems
Engine Parts Lubricated by Engine Oils

Functions of Engine Oil
Provision of stable oil film between moving surfaces
It prevents direct metal to metal contact by creating a continuous oil film
(hydrodynamic lubrication regime functions as a hydraulic lifters) between two
moving surfaces like rotation of crank shaft and engine bearings, reciprocating
motion of piston rings over cylinder liner inner wall, various gears arrangements,
etc. It reduces the coefficient of friction as the oil film keeps moving surfaces away
from each other and that ease the movements of moving parts producing less
heat. It helps to evenly distribute load applied bearing over its surface, cools down
the sliding parts. It takes foreign particles away from the friction region
Provision of reliable engine operation in a wide temperature range
Viscosity of oils strongly depends on its temperature. Again the oil film thickness
depends on oil viscosity. When an engine starts at low temperature the oil is
viscous (Thick). If the viscosity is too high the oil will not be able to flow to the
sliding parts and the non-lubricated engine will not run.
On the other hand oil viscosity in an heated engine is low. The oil flows easily,
however the oil film thickness of hot oil is low, and it may become less than the
roughness of the sliding surfaces. In this case hydrodynamic lubrication regime is
broken and direct metal to metal contact between the surfaces occurs. Metal to
metal contact causes excessive wear, overheating and even fatigue of the sliding
surfaces. Hence, lubrication is formulated considering the requirement in both
cases.

>> Rust / Corrosion protection in engine components
Combustion gases containing water vapors and other chemically active gases partially
penetrate to the crankcase and may cause corrosion. In addition to this some constituents of
combustion gases dissolve in the oil and increase acidity. Such oil may become aggressive to
the metal parts contacting with it. Corrosion inhibitors are added to engine oils in order to
provide protection of metallic (both ferrous and non-ferrous) parts.
>> Cleaning the engine components from sludge
Combustion gases past through the piston rings to the crankcase contain some
amount of not burnt carbon which may deposit on the rings, valves and cylinders,
forming sludge. The sludge clogs oil passages and clearances decreasing
lubrication of the engine parts. In order to remove the sludge from the surface,
detergents are added to the engine oils. Dispersants, which are also added to the
engine oils, help to maintain maintained removed sludge and other contaminants
(both ferrous and non-ferrous) in form of fine suspension permitting engine
functioning between the oil changes.
>> Sealing Piston Ring- Cylinder Gap
Imperfection on the surfaces of the piston rings and cylinders walls result in
penetration of combustion gases in to the crankcase, which decreases the engine
efficiency and cause contamination of the oil. Engine oil fills these microscopic
passages and seal the ingression of combustion gases.

>> Prevention of Foaming
Engine oil circulating in an engine may entrap air and form foams. Foamed oils
are less effective in their important functions (oil film formation, heat removal,
cleaning). In order to diminish foam formation special additives anti-foaming
agents are added to the engine oils.
>> Cooling the Engine Parts
Combustion heat and friction energy must be removed from the engine in order to
prevent its overheating. Most of heat energy is taken by the engine oil. Clean oil
passages, proper viscosity and low contamination provide sufficient flow rate of
the engine oil and effective cooling.

Surface Roughness, Friction and Lubrication
To understand the working principle of lubricants, first of all you have to be familiar with the
nature of the two surfaces to be lubricated.
Whenever a surface is machined (no matter how sophisticated tools are being used) there will be
tiny microscopic irregularities in the machined surface. The nature of these irregularities will
vary depending upon the materials, machining process (i.e. rolling, turning, grinding, milling or
plateau honing, lapping, but the net effect is the same. Under microscopic examination, the
surface is anything but smooth. When two such surfaces are forced to slide over each other,
opposing high spots (known as asperities) will contact, resisting any sliding motion. The contact
invariably alters the surface of the mating parts due to distortion, scuffing, micro-welding and
subsequent tearing. An engine or any machine operated under such conditions would not last
long without corrective maintenance
Figure: Surface roughness in different machining operation

Figure: Microstructure of polished liner surfaceFigure: Polished (by honing) liner surface
Visual Appearance of cylinder
liner surface
Microscopic Appearance of
cylinder liner surface

Video Clip To Illustrate Friction and Lubrication

Types of Metal Contacts
Rolling contact takes place in
ball and roller bearings and in
gear drives. As shown in figure ,
large compressive forces act
between the component
surfaces. The lubricant is swept
into the contact zone by the
rolling motion.
Particles larger than the
thickness of the lubricant film
separating the opposing
surfaces indent and pit the
surfaces.
Figure: Schematic Diagram of Rolling Contact
There are three types of relative motion which can take place between diesel engine component
surfaces.
>> Rolling Contact
>> Sliding Contact
>> Squeeze Contact

Sliding Contact
Sliding Contact takes place in journal bearings and ring-cylinder contacts. During sliding
contact the lubricant is swept into the contact zone by the relative motion of the two surfaces.
The presence of particles larger than the dynamic film thickness leads to severe
abrasive wear. Hard particles cut away material from the component surfaces, with the
simultaneous generation and release of new contaminant particles into the fluid.

Squeeze Contact
Squeeze Contact takes place because of linear forces and vibration. The valve-to-cam
follower contact is a good example. In squeeze contact, motion perpendicular to the opposing
surfaces forcing lubricant in and out of the contact zone. Particles caught between the surfaces
will roughen and dent the components. This leads to abrasive removal of material, fretting,
and fatigue.

Dynamic Clearances and Critical Film Thickness
In lubricated contacts, dynamic clearances are maintained by
oil films between moving surfaces. The lubricant film
thickness, as shown in Figure , is the distance between the two
moving surfaces. Compressive forces (the load) act to push the
moving surfaces together. Tangential forces (shear) tend to
displace the surfaces horizontally. A film of oil supports the
load between the opposing surfaces and keeps them separated.
The thickness of the oil film is related to the mode of
lubrication that we will discuss in subsequent slides.

Particle Size Distribution in Used Diesel Engine Oil
Figure: Particle Size Distribution
in Used Engine Oil
Based on above figure, more than 99% of these particles are less than 20 micron in size

ISO 4406:1999 Cleanliness Rating Number
What is the meaning of “micron” in particle size? Below figure can help your
perception about micron size
The cleanliness rating of engine oils is measured via the lube oil particle count. Most
particle counter reports results at six particle diameter size ranges: 4µ, 6µ, 14µ,
21µ, 38µ and 70µm. An ISO Cleanliness rating number is derived from the results
of three smallest sizes, therefore the minimum particle count test should furnish
results at 4µ, 6µ, 14µm. Before discussing about particle size we need to refocus our
perception about micron size.

ISO 4406:1999 Cleanliness Rating Number
What Actually The Code Represents?

Chain Reaction of Wear
Breaking The Chain Reaction Of Wear:
In a study by Dr. E. Rabiniwicz of M.I.T., the observation was made that 70% of component
replacements or "loss of usefulness" is due to surface degradation. In hydraulic and lubricating
systems, 20% of these replacements result from corrosion, with 50% resulting from mechanical
wear.
Particles generated as a result of abrasive wear are work hardened; thus they become harder
than the parent surface. If these particles are not removed by proper filtration, they
will recirculate and cause additional wear. This "chain reaction of wear" will continue and result
in premature system component failure unless high-performance filtration is applied to break
the chain.
92U235 + 0n1 → 3 0n1 + 36Kr92 + 56Ba141 + ENERGY
Uncontrolled Fission Chain Reaction Controlled Fission Chain Reaction
Most reactors are controlled by means of control rods
that are made of a strongly neutron-absorbent
material such as boron or cadmium

Lubrication Methods
Types of Lubrication Methods
 Boundary Lubrication
 Hydrodynamic Lubrication
 Elastohydrodynamic Lubrication
Engine Parts Lubricated By Engine Oils
 Piston Motion in Cylinder
 Crankshaft Rotation in Engine Bearings (Main Bearings and Big End Bearings)
 Piston Pin Rotation in the Bush of Small End of the Connecting Rod
 Camshaft Rotation in Camshaft Bearings
 Cams Sliding Over the Valves Rods
 Intermediate Gears
 Turbocharger Bearings
 Pedestal Bearing
 Reciprocating Motion of Valve Stems

Coefficient of Friction and Types of Lubrication
The relationship between friction, pressure, speed and lubrication is expressed as the
coefficient of friction.
The coefficient of friction is found by dividing the force required to move a body over a
horizontal surface at constant speed by the force holding the body against the surface.
Coefficient of Friction (F) = Lubricant Viscosity (Z) x Speed (N)/ Perpendicular Load (P)
Against Surface
The lubricant viscosity is a measure of its
resistance to flow. As the number of asperities
on the surface increases the coefficient of
friction increases.
Higher the coefficient of friction means more
force is required to move parts over another
surface because of the increase in frictional
drag force.
The additional power required to overcome
this frictional drag is wasted resulting an
inefficient operation and wastage of additional
energy. Excessive friction increases heat, wear
and component damage depending on the
severity of operating conditions.
Streibeck Curve shows the effects of
viscosity, speed and load on friction.

Fluid Film or Hydrodynamic Lubrication
Under conditions of fluid film or
hydrodynamic lubrication the oil is
swept into the contact zone by the
relative motion of opposing
surfaces. The lubricant film, usually
larger than 2 microns, develops up
to 50,000 psi pressure in the
contact zone. This pressurized film
supports the load between
component surfaces. There is little
or no deformation of the
component surfaces in the contact
zone. Studies show that wear rates
and particle generation are less
when the ratio of film thickness to
surface roughness (average height
of asperities) is greater than three
to one. Under these circumstances,
mechanical surface wear is
negligible unless solid particles the
size of or larger than the oil film
thickness are present.

Boundary Lubrication
Figure, illustrates the conditions that exist
during boundary lubrication. Low speeds, high
loads, and squeeze contact between component
surfaces can starve ,the contact zone of
lubricant. In addition, start up, shutdown, and
high temperature thinning of the oil are duty
cycle conditions that can lead to oil starvation.
The remaining lubricant film between the
surfaces is 0.001 to 0.05 microns thick. High
stress or heat at the asperity contact sites may
displace this boundary layer of lubricant,
leading to adhesive wear. Because of the
extremely thin film, very fine particles can
cause surface damage. It is important to note
that a component can shift between the three
modes of lubrication several times during a
single duty cycle.
The EP additive is active under heat and pressure.
This EP additive reacts with metal surfaces to form a
protective film. This film coats the microscopic peaks
on the interacting surfaces. This film has low shear
strength but high solid to liquid transition
temperature. It acts as a sacrificial wear layer
reducing friction between interacting components
and protecting them from excessive wear.

Elastohydrodynamic or EHD Lubrication
Under conditions of elastohydrodynamic lubrication the oil is swept into a highly loaded
concentrated contact where lubricating film thickness varies between 0.05 and 2 microns. In the
contact zone there is considerable elastic deformation of the surfaces. The fluid film at the
contact zone develops as much as 350,000 psi pressure. This extreme pressure greatly increases
the viscosity of the oil within the contact zone. The high pressure in the contact zone causes solid
particles the size of or larger than the lubricant film to indent or furrow deeply into the
component surface.
Two things happen in EHD
lubrication; first the surfaces in
contacting parts deformed
elastically spreading the load
over a wide area; second the
viscosity of lubricant in this area
momentarily increases
dramatically increasing its load
carrying ability in the contact
zone. The combined effect is to
trap a thin but very dense oil
film between interacting
surfaces. As viscosity increases,
sufficient hydrodynamic force is
generated to form a full fluid
film and separate the surfaces.

Different Lubrication Regimes
Video Clip To Illustrate Different Lubrication Regimes

Types of Contaminants
Lubricant contaminants degrade the life and performance of diesel engines. These
contaminants fall into three
categories:
1. Solid particles, including wear debris, which damage
mechanical components and catalyze lubricant
breakdown.
2. Liquid contaminants, including fuel and water, which hinder the proper operation
of the lubricant and its additives.
3. Gaseous contaminants, including combustion products, which corrode component
surfaces and break down the oil.
The predominant types of diesel engine oil contaminants, along with primary sources
and major problems these
impurities cause, are listed in next slide

Contamination of Diesel Lube Oil

How Contaminants Enter in Lubricant?
Contamination enters the engine lube system by four routes:
1 ) built-in from manufacture and assembly, 2) Maintenance Activities 3) External
Ingression, and 4) Internal Generation
Built-in Contamination:
Diesel engine manufacturers take great care during the manufacture and assembly
processes to ensure high quality control. However, casting materials, machining
swarf, abrasives, polishing compounds, and even lint remain after manufacture and
overhaul. These built-in contaminants can rapidly damage moving engine parts.
Maintenance Activities:
During maintenance activities contaminants are introduced into the lubrication
system. Opening rocker covers, the engine head, even the oil filler cap allows
entrance of dust and water. Simply making and breaking a fitting generates tens of
thousands of damaging particles. In addition, new oil contains contaminant particles

Ingression of Lubricant Contaminants
External Ingression:
External ingression is a major source of hard particle contamination. Airborne
particles, in the form of sand, salt, and other minerals, enter through the engine
intake system and mix with the atomized fuel, which is compressed and then burned.
Since most of these particles have melting points considerably above the
temperatures reached in the diesel combustion process, they remain hard abrasive
solids.
Air-borne contamination has been shown to be the greatest cause of ring-to-cylinder
wear . The strong pressure shock wave created during combustion forces gases
through the piston ring clearances. This process, known as blowby, carries particles
into the engine oil. Particles may also be retained in the oil film. They are then wiped
by the rings into the oil sump on the next down stroke of the piston.
Exhaust gases are similarly driven into the lube oil as blowby gases. These exhaust
gases include unburned fuel, water, nitrous oxide, soot, and other partially burned
hydrocarbons.
Other paths for external ingression of contaminants into the engine oil include
crankcase breathers, which can admit large quantities of dust and water directly into
the oil sump, and diesel fuels contaminated with particles. In addition, water
combined with anti-freeze compounds such as glycol can be forced into the oil cavity
under pressure through defective head gaskets, or, occasionally, through a crack in
the block.

Ingression of Lubricant Contaminants
Internal Generation:
Internal generation of contaminants is by wear of mechanical component parts and
by lubricant breakdown. Mechanical component wear from abrasion, fatigue,
adhesion, and corrosion releases harmful particles into the oil. The wear debris is in
the form of hard metal particles and of abrasive metal oxides. Wear debris particles
of sizes not controlled by standard filtration can build up to grossly contaminate the
lube oil.
Lubricant breakdown is the loss of important properties of the oil plus accumulation
of harmful materials derived from the oil. These materials include acids, sludges,
gels, and additive precipitates. These contaminants can wear moving component
parts as well as clog flow passages and heat exchange surfaces.
If wear debris and materials from lubricant breakdown accumulate in the oil, the
result is more wear, generating more contaminants. The process of particles wearing
surfaces and generating new particles that in turn cause more wear is known as the
chain-reaction-of-wear.

Contaminant Particle Size and Engine Component Wear
There is an important relationship between the size of contaminant particles and the
thickness of dynamic lubricant films separating opposing surfaces. Particles the size of
and larger than the lubricant film thickness cause wear of component surfaces. These
particles bridge the gap maintained by the oil film, making simultaneous contact with
both surfaces. This focuses the force between the surfaces, causing damage and resulting
in component wear. An extensive survey of the technical literature for oil film thicknesses
in diesel engine components is summarized in Table 2. Most of these dynamic clearances
are between 0 and 20 microns. Contaminant particles the size of or larger than these
dynamic clearances produce a major portion of the wear experienced by diesel engine oil
wetted components.
Based on above data, particle size 0 – 10 micron
are more damaging than larger particles.

Mechanism of Wear
There are five forms of wear that occur in diesel engine components: abrasion,
fatigue, adhesion, corrosion, and lubricant breakdown. Abrasion, fatigue, and
adhesion involve mechanical damaging of surfaces; corrosion and lubricant
breakdown involve chemical reactions.
Abrasion:
Abrasive wear by contaminant particles
involves the rapid cutting away of
component material an abrasive particle
abutting one surface slides along and
ploughs through the opposing surface.
Material is cut away in a single pass. The
rate of abrasive wear is proportional to the
number of contaminant particles the size of
or larger than the dynamic lubricant film.
The results of abrasive wear are: roughened
surfaces, loss of clearance, misalignment,
and generation of fresh wear debris.
Particles generated from this process are
similar to microscopic machine chips. These
particles add to the oil contamination and
accelerate the chain-reaction-of-wear

Mechanism of Wear
Mechanism of Abrasive Wear:
Abrasive wear is the primary wear
mechanism. Particles enter the clearance
between two moving surfaces, burry
themselves in one of the surfaces, and act
like cutting tools to remove materials from
opposing surface. The size of particles
causing the most damage are those equal
to and slightly larger than the clearance.
Most diesel engine components have
dynamic clearances less than 20
micrometers. To protect opposing surfaces
from abrasive wear and fatigue, particles of
approximately this clearance size range
must be removed deploying appropriate
equipments.

Mechanism of Wear
Fatigue:
Fatigue of a component surface is due
to an accumulation of microscopic
cracks at or just below the component
surface. These cracks accumulate
over an operating period, eventually
combining to form voids which
undermine the surface. Large
quantities of material then break
away, leaving a cratered surface and
releasing work hardened particles
into the oil which continue the chain
reaction-of-wear. As shown in Figure,
by focusing the force between loaded
surfaces, particles larger than the
lubricant
film dent and crack the surfaces. For
component surfaces in rolling or
squeeze contact, surface fatigue
caused by particles may be the
primary wear mechanism.
Particle is caught Surfaces dented, cracking initiated
After fatigue cycles, cracks spread Surface fails, particles released

Mechanism of Wear
Adhesion:
Adhesive wear occurs when the boundary
layer lubricant film between the
asperities of two opposing surfaces is
displaced. This is shown in the Figure.
Metal-to-metal contact between surfaces
can lead to spot welding of these
asperities. As the asperities of the moving
surfaces part, the microscopic spot welds
often break asymmetrically, removing
material from the surface with the lower
yield strength.
The result is high friction, wear, and heat
generation. If a large number of spot
welds are produced simultaneously, the
surfaces can no longer move apart and
seizure occurs. Degradation of surfaces
by particles, such as roughening and
misalignment, can lead to surface-to-
surface contact and adhesive wear.

Mechanism of Wear
Corrosion:
Corrosion is a reaction between aggressive chemicals and component surfaces.
Aggressive chemicals include water, dissolved oxygen, and NOx, SOx from the
combustion gases. Two mechanisms by which corrosion degrades surfaces are: 1)
the reaction products dissolve in, and are removed by the lubricant, and 2) the
reaction products form a brittle crust, often of abrasive metal oxides, which breaks
away from the surface. Particles from these corrosion crusts add to the lubricant
contamination, accelerating the chain-reaction of- wear.
Corrosion is often accelerated on surfaces damaged by contaminant particles. These
worn surfaces have cracks that allow corrosive chemicals to penetrate through
protective surface films and react with the underlying material
Lubricant Breakdown:
Lubricant breakdown is the loss of important oil properties, such as viscosity, and the
build-up of harmful materials derived from the lubricant. Lubricant breakdown can
be caused by several mechanisms. Fuel and water can mix with the lubricating oil to
form precipitates and gels. Soot particles, carried into the lubricant with blowby
gases along with wiping of the piston-rings, can combine with anti-wear and viscosity
additives in the oil to reduce wear tolerances(5) and increase viscosity(6). It has been
shown that particles of fresh wear debris have catalytic surfaces that accelerate oil
oxidation. Oxidation of the oil leads to varnishes, sludges, and increased oil acidity.

Diesel Engine Component Wear
Piston Rings/Cylinder Wear:
The piston-rings have a reciprocal sliding motion. The outside of most piston-rings
is rounded and chrome-plated to produce the best oil film thickness and wear
resistance. As the pistons start to move in the cylinders, a hydrodynamic oil film is
formed between the ring and cylinder surfaces which helps to prevent wear

Piston Rings/Cylinder Wear (Cont’d):
When there is little or no relative motion between the rings and the cylinder (e.g.
prior to start and at TDC and BDC), the fluid film is thin. This is when wear will most
likely occur, since the oil is being squeezed from the contact area.
When the piston reaches the bottom of its travel, the walls of the cylinder are
completely exposed to the high temperatures and products of combustion, as well as
to contaminant particles ingressed with the air and fuel. The thin layer of lube oil left
by the previous pass of the piston may also become partially oxidized. Deposits
formed are either expelled in the exhaust on the upstroke or are swept into the oil
sump by the piston rings on the downstroke. When the piston reaches the top of its
stroke, new oil is splashed or sprayed onto the walls of the cylinders washing a
portion of the previously contaminated oil film into the sump.
If the combustion by-products and particulate contamination drawn in with the air
and fuel bridge the oil film between the ring and cylinder, wear occurs. Wear
particles can also be supplied to the contact areas by contaminants already present in
the oil. The major sources of these contaminants are prior blowby, lubricant
breakdown, and component wear. Particles generated by wear between piston-ring
and cylinder range up to 30 microns in size and are work-hardened. These particles
are abrasive to other engine components as well as to the rings and cylinders

Piston Skirt/Cylinder Wear:
Contact between the piston skirt and the cylinder or liner is often overlooked as a
form of wear. Scuffing can occur between these two parts during cold starts and other
severe operating conditions. Particles generated by this type of contact are quite
abrasive as a result of work hardening and can range in size from silt to 60 microns
and larger. These metal particles contribute to the chain reaction-of-wear, causing
extensive damage if not controlled

Plain Bearings:
Plain bearings are used to support the cam and main drive shafts and to transmit the
power delivered to the drive shaft by the piston and rods. Average oil film
thicknesses are approximately 4-5 microns.

Plain Bearing Wear:
Plain bearings are also used on many
accessories, such as turbochargers and oil
pumps. Another form of plain bearing is the
thrust bearing used in turbo-chargers. This
sliding contact bearing absorbs the high axial
loads generated by the turbocharger
compressors. Most plain bearings have a soft
running surface applied by the manufacturer to
absorb particulate contamination while
supplying a good cold start self-lubricating
surface. Because of their softness, these
surfaces depend on the lube oil film thickness
to prevent wear. Hard contaminant particles
can embed in the soft liner of the bearing
If securely embedded in the bearing and large enough to bridge the oil film
thickness between surfaces, this hard particle contamination causes wear of the
journal. If the particles are larger than the oil film thickness but are not securely
embedded in the soft bearing surface, they can score both the bearing and journal
by a tumbling abrasive action. As shown in Slide XXX, test data indicate that a
majority of wear on diesel engine plain bearings is caused by particles 10 microns
and smaller.

Wear in Valve Train:
The valve train functions to open and close the intake and exhaust
ports to the combustion area at a specified time. The rotational
sliding speed and high lifting loads between the cam lobes and
follower cause lubrication problems. In many diesel engines, this
cam-to-follower interface receives the heaviest wear because of low
oil film thicknesses. Extremely small particles circulating in the lube
oil can bridge the space between the surfaces and cause wear.
Location of the valve train at the top of the engine also generates
extensive carbon deposits due to heat. These carbon deposits have
been shown to adversely affect the anti-wear additives in the oil.
Stiction of the valve in the valve guide can lead to extensive power
loss. Stiction is produced by carbon deposits and hard particles
lodged between the valve and guide. This causes the timing of the
port openings and closings to vary, causing incomplete combustion
in the cylinder as well as combustion in the exhaust manifold
(backfiring). Even if stiction is temporary, permanent power loss can
result from a burnt valve seat.
Rocker arms and followers are often supported by plain bearings. These bearings are lightly
loaded and have restricted movement. However, high temperatures and poor lubrication
produce small lubricant film thickness and lead to severe abrasive wear problems (scoring).
Under cold start conditions, the lube oil can take several minutes to reach these rocker arm
bearings, further reducing film thickness.

Wear in Accessory Drives:
Many diesel engine accessories are gear
driven. These gears shift from sliding to
rolling contact and back to sliding contact as
the teeth mesh and then separate. While
driving relatively light loads, the contact area
of these gears is quite small so contact
pressure is high. With lubricant
contamination larger than one micron,
scoring abrasive wear occurs in the sliding
contact areas and fatigue and abrasive wear
occur under rolling contact. Oil pumps are
also subject to wear between the housing and
sides of the gears, which have a circular
sliding friction contact with a typical
clearance of approximately twenty-five
microns

Key Parameters Strongly Related with Engine Health
Viscosity:
The lubricant viscosity is a measure of its resistance to flow. As the number
of asperities on the surface increases the coefficient of friction increases.
Higher the coefficient of friction means more force is required to move parts
over another surface because of the increase in frictional drag force. The
additional power required to overcome this frictional drag is wasted
resulting an inefficient operation and wastage of additional energy.
Excessive friction increases heat, wear and component damage, lubricant
breakdown depending on the severity of operating conditions,

Total Base Number - TBN:
This TBN is only relevant to diesel engine lubricants. It is not relevant for gear oils or hydraulic
oils. Alkaline additives are present to neutralize acids derived from both combustion (mainly
strong Sulphuric and Nitric acids) and those weaker, organic acids resulting from oxidation of
the oil as occurs during ageing.
TBN is a measurement of the capacity of engine oil for neutralizing strong acids from
combustion of fuel oil. It is not a measure of how alkaline an oil is (the alkalinity is more akin to
soapiness than strong alkali) but it instead measures the alkaline reserve of the oil or its ability
to neutralize acids.
The TBN of trunk piston diesel engines (high and medium speed) will fall due to exposure to
combustion products but generally reaches a stable level as consumption of TBN by
neutralization is matched with replenishment by fresh oil top-up. TBN of system oils in large 2
stroke cross head type engines may rise due to contamination of the oil with very high TBN
cylinder oil draining, via the stuffing boxes or from top-up with incorrect oil grades.
A drop of around 50% of fresh oil TBN indicates that the oil is almost at the end of its useful
life. Another useful indicator is a minimum TBN equal to 7 times the sulphur content of the fuel
in use. Oil suppliers usually recommend a change or partial replacement at this level in order to
optimize the acid neutralizing properties of the oil. This recommendation is mostly based on
engine manufacturer’s advice.
Low TBN reserves provide insufficient neutralization capacity leading to corrosion of engine
components particularly around the piston ring pack, piston ring lands and top end bearing.
Fouling of the engine internals and under piston cooling ways may also increase.

Total Base Number – TBN (Continued):
TBN in gas-fuelled engines is often achieved using a very low ash additive pack. Additives are
often based on automotive practice using magnesium in preference to calcium salts. Low ash
properties are specified, as hot ash on combustion components can result in pre-ignition of the
gas during the induction or compression strokes. TBN in these applications can fall very rapidly
due to high operating temperatures and, if using land fill gas, contaminants in the fuel itself.
Causes of rapid TBN depletion
 Low oil consumption
 Small sump volumes
 High fuel sulphur levels
Another silent reason for rapid TBN depletion is excessive lube oil
contamination especially by Soot and Wear Debris. These two
contaminants acts as a catalyst to break down the lubricant in the
presence of elevated temperature and high pressure and produces various
organic acids which are also responsible for rapid TBN depletion. Hence,
efficient removal of contaminants from lube oil will definitely increase oil
service hours, minimizes lube oil consumption and ensure better protection
to engine components.

Abrasives – Soot/Wear Metals/Dirt:
Soot, sub-micron sized particles produced from incomplete combustion of
fuels in diesel engines.
How Soot(a sub-micron sized particle)/Wear Metals/Dirt Particles Affect
Your Engine Performance
1. They act as a catalyst to breakdown lube oil followed by destroying the
effectiveness of lubricating oil
2. They Actively Participates in Rapid Filter Clogging
3. They Reduces Oil Service Life and Indirectly Equipment Service Life.
4. They Play an Active Role in TBN Depletion.
5. Existing MDC Type Lube Oil Separators are quite inefficient to remove
soot (a sub-micron sized particle) and other particles sized below 5
microns. But Pressure Powered Centrifugal Oil Filters are very effective
in removing such types of sub-micron sized particles. In subsequent
slides we will discuss in detail about the performance of different fluid
filtration system.

Lube Oil System in Large Diesel Engine
Lube Oil Separator
Unit
Full Flow Filters
Engine Driven LO
Pump
Electric Driven LO
Pump
HP Relief Valve
Lube Oil Cooler

Full flow filters
Full Flow Filtration
Full flow filters are the most common type, and receive all, or nearly all the oil
pumped around the engine. They provide essential engine protection for maximum
cold flow performance and filter life. Full flow filters need to be able to provide good
filtration, handle the required flow rate even when the oil is cold, and provide
adequate dirt holding capacity. The use of synthetic media or cellulose media
filters are very common.
By-pass (secondary) Filtration
Sometimes referred to as a secondary filter, a by-pass filter is usually fitted to a
separate line where a small portion, usually of about 5 – 10% of the total oil flow,
passes through them and is then diverted back to the sump. A bypass filter is usually
a much finer filter to capture smaller particles than the full flow. Because it has a
higher efficiency, it will have a much lower flow rate than a full flow filter; especially
when the oil is cold. It is designed to improve the overall cleanliness of the oil
without compromising the flow rate to the engine.
Two-stage Filtration
A two-stage filter design attempts to combine the features of both a full flow and a
by-pass filter. The two-in-one design significantly increases restriction, causing
shorter filter life and decreased cold flow performance. Poor cold flow performance
starves the engine of oil during start up, leaving the engine temporarily unprotected.
This will lead to increased engine wear that may result in premature repairs or even
engine replacement.

Lube Oil System in Diesel Engine
Lube Oil
Separator
Unit
SEPARATORINLET
SEPARATOROUTLET
SLUDGE

Typical Full Flow Filter Elements
Stainless steel wire mesh,
wedge wire profiles
Filtration Grades: 3 µm - 50 µm,
Paper, Polyester, Fiber glass made
disposable cartridge used for flushing
liquid treatment

Reverse Flush Self Cleaning Filter (RFSCF) (Automatic Filter)
Mud Box Filter:
Filtration Grades: 3 µm - 50 µm, Paper, Polyester, Fiber glass
made disposable cartridge used for flushing liquid treatment
Automatic Filter:
Filtration Grade: 35 µm , Stainless steel wire mesh, wedge wire profiles
Internal Candle ElementsBOLL & KIRCH Filterbau Automatic Filter
Mud Box Filter

Lube Oil Safety Filters (Once Through Duplex Type)
Duplex Type Once Through Lube Oil Safety Filter:
Filtration Grade: 60 µm , Stainless steel wire mesh, wedge
wire profiles
Candle Elements for Lube Oil
Safety Filter:
Filtration Grade: 60 µm , Stainless
steel wire mesh, wedge wire
profiles

Expectation on Full Flow Filters
•It will permit sufficient flow of Lube Oil to the system
•It will ensure pressure drop as minimum as possible
•It will ensure removal of suspended particles as maximum as possible to
protect engine components
•It will provide extended service life followed by minimizing downtime
•It will be easily cleanable
We have seen various full flow filters present in diesel engines. What we expect
from a full flow filters?
Based on our expectation, Providing Maximum Removal of Particles with Less
Pressure Drop is Two Opposite Constraints for a Full Flow Filters
To provide sufficient flow, pressure drop to be as low as possible. So the mesh size
must be quite large. Again, to remove contaminants from lube oil as maximum as
possible, the mesh size must be as small as possible to protect engine
components. Hence both opposing constraints to be optimized.
To optimize opposing constraints, some contaminants have to allow through full
flow filters. So, introducing a bypass filter/lube oil separator is vital for removal
of those particles which are not possible to separate by full flow filters.

Engine Manufacturer’s Recommendations For Lube Oil System
Filters in Internal Lubricating Oil System:
For Example WARTSILA 18V46 Engine Lube Oil System
As a standard the engine is equipped with a built-on side stream centrifugal filter
and starting-up/running-in filter(s)
Centrifugal filter:
The centrifugal filter in by-pass is used as an indicator filter.
• Capacity per filter 3.5 m³/h
• Filtering properties down to 1m
Starting-up or running-in filter:
All engines are provided with a full-flow paper cartridge filter in the oil inlet line to
each main bearing. The cartridge is used only during running-in and at the first
starting- up of the installation
Is your engine equipped with Centrifugal Filter?

Filters in External Lubricating Oil System:
For Example WARTSILA 18V46 Engine Lube Oil System
Suction strainer >> Fineness 0.5 - 2.0 mm
Automatic filter
An automatic self-cleaning filter must be installed.
Design data:
Lubricating oil viscosity : SAE 40
Operating pressure : max. 8 bar
Test pressure : min. 12 bar
Operating temperature : max. 100°C
Fineness 90% separation : above 20 micron)
(absolute mesh width : max. 35 micron)
Max. permitted pressure drop for normal filters:
– clean filter : 0.3 bar
– alarm : 0.8 bar
Automatic Filter:
Filtration Grade: 35 µm , Stainless steel wire mesh, wedge wire profiles

Lubricating oil safety filter
The lubricating oil safety filter is a duplex filter with steelnet filter elements.
Design data:
Lubricating oil viscosity : SAE40
Operating pressure :max. 8 bar
Test pressure : min. 12 bar
Operating temperature : max. 100°C
Fineness 90% separation above 50 m at once through flow
(absolute mesh width max. 60 m)
Max. permitted pressure drop for normal filters:
– clean filter 0.3 bar
– alarm 0.8 bar
Duplex Type Once Through Lube Oil Safety Filter:
Filtration Grade: 60 µm , Stainless steel wire
mesh, wedge wire profiles
Candle Elements for Lube Oil Safety
Filter:
Filtration Grade: 60 µm , Stainless
steel wire mesh, wedge wire profiles

Lube Oil Separator
Lube Oil Separator
The separator should be dimensioned for continuous centrifuging. Each lubricating oil
system should have a separator of its own.
Design data:
Lubricating oil viscosity : SAE 40
Lubricating oil density : 880 kg/m3
Centrifuging temperature : 90 - 95°C
The following rule, based on a separation time of 23
h/day, can be used for estimating the nominal capacity
of the separator:

What is Centrifuge Turn Rate?
Separator Turn Rate is the ratio of total hourly centrifuge flow rate divided by total
engine lube
Turn Rate TR = Total Hourly Flow Rate / Total Sump Oil Volume
For an example the Turn Rate of a Pressure Powered Centrifuge:
Engine : Cat D399
Engine Speed : 1200 rpm
Lube Pump Flow : 163 gpm
Crankcase & Accessory Capacity : 135 gallons
Centrifuge Flowrate : 8 gpm
Turn Rate : 3.5 turns per hour
For an example the Turn Rate of a Motor Driven Centrifuge:
Engine : WARTSILA 18V46
Engine Speed : 500 rpm
Engine Output : 16.3 MW
Lube Pump Flow : 289 m3/h
Crankcase & Accessory Capacity : 14.0 m3
Centrifuge Hourly Flow Rate : 4.763 m3/h
Turn Rate : 0.34 turns per hour

Filter Ratings
Beta Ratio (ß) How Many Particles of a Given Size Will Pass Through the Filter? Actual Filter Efficiency
2 1 out of every 2 particles 50%
75 1 out of every 75 particles 98.67%
The efficiency of a liquid filter on a given particle size is frequently described as either a Beta
ratio (ß), or as a percentage (%). Both the Beta ratio and percentages of efficiency compare the
amount of contamination before and after the filter. The table below provides the efficiency
percentages of the commonly used Beta Ratios.
Generally, efficiencies are not provided for micron ratings or particle sizes smaller than 3
micron. When looking at the different fuel filters, it is important to compare apples with apples
when considering filtration performance.

PART 2
CONTAMINATION
CONTROL GUARDS IN
DIESEL ENGINES
This Part in Under Construction

Diesel Engine Lubrication and Lube Oil Contamination Control

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