Woodyard D. (ed.) Pounders Marine diesel engines and Gas Turbines
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128 Fuels and Lubes: Chemistry and Treatment
It is the responsibility of the ship owner/manager’s technical department
to ensure that ships’ engineers are aware of oil stress, the symptoms to look
for and how to prevent it occurring. If the lube oil is operating under highly
stressed conditions, its properties change and deteriorate more quickly than
oils operating under less stressed conditions. Minimizing oil stress-related fail-
ures or preventing them entirely dictates maintaining the lubricant in the best
possible condition, and that can only be ensured by well-trained and motivated
shipboard staff.
synthetic Lubricants
The vast majority of marine lubricants are still formulated with mineral bases,
but the development of synthetic lubricants targets enhanced machine running
safety and durability and the extension of oil change intervals. Such products
are particularly valued for harsh duties and are applied widely in aviation,
high-speed trains and Formula 1 racing cars.
Synthetic lubricants are made from synthetic base oils derived from the
chemical reaction of one or more products, supplemented by special additives
incorporated to boost performance properties. These base oils may be formu-
lated from synthetic hydrocarbons, organic esters, polyalkylene glycols, phos-
phatic esters, silicates, silicones and fluorosilicones, polyphenyl esters and
fluorocarbons.
Marine industry applications currently embrace reciprocating and rotary
auxiliary machinery such as turbochargers, air compressors, refrigeration com-
pressors, LPG/LNG compressors and centrifugal separators. Some high-speed
ferry engines also exploit synthetic lubricants.
Exxon Mobil’s synthesized hydrocarbon (SHC) lubricants, formulated from
pure chemical lubricant base stocks and special additives, promise the follow-
ing advantages over mineral oil products:
l Wax-free, underwriting low-temperature performance
l Relatively small viscosity changes with temperature, and completely
shear stable
l Excellent oxidation resistance, providing superior wear protection
l Significantly extended service life
l Ability to handle greater loads, higher speeds and more extreme
temperatures.
These benefits reportedly translate into reduced overall operating costs and
lower machinery downtimes.
Low chlorine, zinc-free Mobilgard SHC 1 is formulated as a crankcase oil
for distillate-fuelled high- and medium-speed engines in installations subject to
low temperature and/or frequent starts, rapid loading after start-up, and abrupt
shutdown after high-speed operation. The lubricant requires no changes in
seals, hoses, paints or filters; no flushing is necessary and the oil is fully com-
patible with hydrocarbon products. Extensive heavy-duty field tests with MTU
high-speed engines in fast ferries are said to have demonstrated the ability
to reduce engine wear, extend draining intervals and lower fuel consumption.
Mobilgard SHC 1 can also be used in gearboxes.
Cylinder Lubricants and Low-sulphur Fuels
SECAs (see Low-Sulphur Fuels) impact on cylinder lubrication in low-speed
engines since the fuel dictated to meet emission controls is generally limited
to a maximum 1.5 per cent sulphur content. Advice on lubricating low-speed
engine cylinder liners in a regulatory environment imposing widely different
fuel sulphur levels is offered by Chevron Global Lubricants.
Cylinder lubricants in two-stroke engines have a number of functions: they
are designed not only to achieve good lubrication and internal cleanliness but
also to neutralize the sulphuric acid formed in the combustion chamber. The
total amount of base introduced into an engine by the cylinder lubricant should
match the amount of acid produced, which depends on the fuel sulphur content.
If the engine is burning high-sulphur fuel, the amount of sulphuric acid pro-
duced will be high as well. If the total amount of base provided to the engine is
low compared with the amount of acid produced, corrosive wear will increase
and steps will have to be taken to raise the cylinder oil feed rate so that more
base becomes available.
When the engine is burning low-sulphur fuel, it will produce less acid. At
equal oil feed rate, the amount of base fed into the engine will be much higher
than that required to neutralize the acids produced. As a result, the amount
of instantaneous wear will be low. At the same time, however, the additives
responsible for this excess in base will be burnt in the combustion chamber,
resulting in the formation of a thick layer of ash on the piston top land. This
could eventually interrupt the oil film and promote abrasive polishing of the
liner surface and ring/liner scuffing.
High oil feed rates were traditionally viewed as beneficial because they
were thought to provide a greater margin of safety against excessive wear and
sticking rings, as well as improving piston cleanliness. It is now accepted,
however, that the optimum feed rate is the minimum consistent with acceptable
wear in the engine. Apart from adding to operating costs—cylinder lube oils
are expensive—oil feed rates that are higher than necessary can lead to exces-
sive deposits and should be avoided.
To achieve the correct balance, a cylinder lubricant with a lower BN can
be selected or the oil feed rate adjusted to the sulphur content of the fuel. The
BN offering has consolidated to a 70 BN product for high-sulphur fuel and a
40 BN or 50 BN product for use with fuel having a sulphur content lower than
1.5–2 per cent. Low BN cylinder lubricants must provide adequate detergency,
dispersancy and thermo-oxidative stability in combination with a low BN. All
the major enginebuilders have issued guidelines for operating on low-sulphur
fuel, giving recommendations on cylinder lubricant BN and oil feed rates.
The operator of a long-haul container ship entering an SECA may choose to
reduce the feed rate. If the ship will not be sailing for more than a month (500
running hours) within the SECA, the engine should be able to run smoothly on
Lubricating oils 129
130 Fuels and Lubes: Chemistry and Treatment
a 70 BN lubricant. Oil feed rate reduction should be effected cautiously and in
several steps, however, taking advantage of port inspections to monitor piston
and cylinder condition.
Below a certain minimum limit prescribed by the enginebuilder, the oil
feed rate becomes too low to secure lubrication and engine cleanliness. If the
engine is scheduled to run on low-sulphur fuel for an extended period, there-
fore, the use of a 40 BN or 50 BN cylinder lubricant is strongly recommended,
especially in modern high output engines. Such engines will obviously be more
sensitive to the mechanism of piston crown deposit build-up than older designs
having much lower mechanical and thermal load levels.
Concern that contemporary cylinder oils (whether 70 BN or lower) might
not be the best choice for service with low-sulphur fuels was addressed by
MAN Diesel and BP Marine in answering the following questions.
shouLD a newbuiLDing be speCiFieD wiTh a DuaL sToRage
anD piping sysTem FoR CyLinDeR oiLs?
Ship owners are advised to seriously consider future operational flexibility for
switching in and out of low-sulphur fuel. To facilitate optimization in various
scenarios, it is sensible to plan ships with dual (or multiple) storage tanks to
allow more than one cylinder oil grade to be carried. The actual tank capacities
may be open to debate but it is useful to start allowing for segregation.
whaT shouLD be Done when Changing oveR To Low-suLphuR
FueL FoR shoRT DuRaTions on RanDom bunKeRs?
If regular inspection shows that 70 BN oil is performing satisfactorily, then
consider remaining on that lubricant; as a caution, however, avoid running-in
on low-sulphur fuel with 70 BN oil, if possible.
whaT shouLD be Done when swiTChing ReguLaRLy beTween
Low anD high-suLphuR FueLs on a RouTine TRaDing RouTe?
As discussed earlier, if there are two grades of cylinder oil onboard (70 BN and
a suitable lower BN grade) then switch accordingly if that is convenient and if
monitoring confirms that yields the best results. This could be the policy when
SECAs become widespread.
whaT shouLD be Done when on pRoLongeD opeRaTion
wiTh Low-suLphuR FueL?
Run on low BN oil and closely monitor to ensure that it gives the best results.
CyLinDeR LubRiCanT FeeD RaTes
Cylinder oil feed rates should be set with a reasonable margin of safety on
the recommendations of the enginebuilder/designer. A high oil feed rate, far
greater than 150 per cent nominal, is seldom required other than for a short
period during running-in or when special circumstances justify it. There have
been reports from both MAN Diesel and Wärtsilä engines that over-lubrication
can in fact be harmful in certain adverse conditions.
MAN Diesel advises that unless there are abnormal circumstances, it is point-
less to pursue prolonged operation with an excess of 2 g/bhp h (2.72 g/kW h),
especially in conjunction with low-sulphur fuel, 70 BN cylinder oil and an
engine series well designed against corrosive wear and with no need for exces-
sive BN. Even for a highly detergent oil, over-lubrication can lead to excessive
calcium carbonate deposits in the remote top edge of the hot piston crown land.
(The BN of all commercial cylinder oils today is derived largely from calcium
carbonate.)
In adverse conditions it is sometimes not the oil detergency that cannot
cope but rather there is an enormous generation of calcium carbonate deposit.
Influenced by MAN Diesel, BP Marine recognized the potential problem of a
high feed rate and excessive calcium carbonate deposition during running-in
and in low-sulphur fuel operation. Its launch of the cylinder lubricant CL-DX
405 addressed such conditions with a reduced BN 40 and reduced calcium car-
bonate, while maintaining very high detergency.
Enginebuilders are also concerned that an engine well designed against
corrosive wear can become sensitive to excessive feed rate on 70 BN oil when
burning fuel with a normal sulphur content. This is because if the BN is not
used, the unused BN can result in hard calcium carbonate deposits (used BN
results in a softer calcium sulphate). Wärtsilä adds that a high cylinder oil feed
rate can lead to a disturbed pressure drop across the ring pack and negatively
affect piston running. Excessive cylinder oil also tends to increase the forma-
tion of deposits on the top land of a piston. A solid crust is formed, which is
softer or harder depending on the additives used in the oil, the type of fuel and
its sulphur content, as well as its combustion characteristics. An excessive feed
rate can, in fact, also lead to the destruction of a scuffing liner within hours.
Another reason for caution over excessive feed rates is that modern engines
are significantly more powerful, burn more fuel and use more cylinder oil per
cylinder than before. The cylinder oil ash level could be more than five times
higher than in engines of the 1970s and 1980s.
‘intelligent’ Cylinder Lubrication
Demands placed on cylinder oil in two-stroke engines vary widely and depend
on the operational conditions. The cylinder of a large bore engine is typically
fed with just 1 g of lubricant during each stroke, and this small amount must be
spread correctly to fulfil all requirements. Studies of the relationship between
wear and lube oil dosage reveal that interaction between operational factors—
such as load variations, fuel and lube oil qualities and atmospheric humidity—
exerts a strong influence on the wear rates of piston rings, ring grooves and
cylinder liners. It has also become clear that over-lubrication has a consider-
able negative effect on the tribological conditions of liners and rings.
Traditional cylinder lubrication systems, whereby the lube oil is injected at
a fixed rate proportional to the engine revolutions per minute or mean effective
pressure and perhaps adjusted occasionally based on a scavenge port inspec-
tion, may yield a reasonable average condition. Such a condition, however,
Cylinder lubricant feed rates 131
132 Fuels and Lubes: Chemistry and Treatment
will result from long periods of excessive lubrication and shorter periods of
oil starvation because the sum of influencing factors will change on a daily
or sometimes even on an hourly basis. Furthermore, there is a risk of ruining
the cylinder condition if unfavourable operational factors are not detected and
properly counteracted by the engine operators.
Operational conditions beyond the norm are unavoidable, and many ship
owners simply over-lubricate their engines under the false assumption that they
will thus always be ‘on the safe side’. But over-lubrication is not only expen-
sive, it may even be counterproductive in promoting scuffing through exces-
sive carbon deposits and/or ‘bore polished’ running surfaces. A wear study has
proved that the optimal basic setting of cylinder lubricators should be propor-
tional to the engine load and the fuel oil sulphur content. Feed rate control pro-
portional to the load is one of the two standard options of MAN Diesel’s Alpha
Lubricator system; the other is to control lubrication in proportion to the mean
effective pressure. Lubricator control in relation to the fuel oil sulphur content
may be carried out either automatically—based on a feed-forward signal from
the fuel inlet line—or manually, based on the sulphur content from the bunker
receipt or fuel oil analysis data.
The electronically controlled Alpha Lubricator was developed to inject the
oil into the cylinder directly on the piston ring pack at the exact time that the
effect is optimal. The system features a number of injectors that inject a spe-
cific amount of lubricant into the cylinder every four (five, six, etc.) revolutions
of the engine. The lubricator has a small piston for each quill in the cylinder
liner, with power for injecting the oil provided from system pressure generated
by a pump station (Figures 4.9 and 4.10).
The properties of cylinder oil scraped from the liner wall reflect the chemi-
cal environment in the cylinders as well as the physical condition of rings and
liner; and there is a direct relationship between some of the key parameters in
the scrape-down oil and the actual cylinder condition. A lubrication algorithm—
based on scrape-down analysis data, cylinder oil dosage, engine load and cyl-
inder wear rate—can thus be created. Automatic optimization of lube oil dos-
age and cylinder lubrication efficiency is facilitated by on-line monitoring of
the scrape-down oil composition from each cylinder, feeding the results into a
computer (along with the above algorithm), and sending signals to each Alpha
Lubricator. Corrosive wear control can be based on either feed rate control or
control of the cylinder oil BN; the latter approach calls for two or more lube oil
tanks or blending facilities onboard.
Alpha lubricators—allowing significantly reduced feed rates over mechani-
cal lubricators—can be specified for all MAN B&W MC/MC-C and ME/ME-C
low-speed engines as well as retrofitted to engines in service. Large bore
engines are equipped with two such lubricators for each cylinder, whereas
smaller bore engines have one unit. Further reductions in cylinder oil consump-
tion are promised from a so-called ‘sulphur handle’, which, in conjunction
with the Alpha Lubricator system, feeds the lubricant in proportion to the
amount of sulphur entering the cylinder (Alpha adaptive cylinder oil control).
Cylinder lubricant feed rates 133
7
10
12
15
20
30
43
52
59
69
87
125
cST. sec.
Rw.
Approximate pumping limit
10 15 25 35 45 55 cSt/100
C
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
C
Approximate viscosity
after heater
Temperature
after heater
Viscosity of fuel
Normal heating limit
30 60 100 180 380 600 cSt/50
C
200 400 800 1500 3500 6000 sec. Rw/100
F
FiguRe 4.8 Fuel oil heating chart (man Diesel)
Outlets for
cylinder liner
lube oil points
Injection plungers
Capacitive feedback
sensor for control of
piston movement
Signal for
lubrication from
control unit
Solenoid
valve
P
T
A
P
A
T
Cylinder
lube oil outlet
45 bar cylinder
lube oil inlet
Actuator piston
Adjusting screw
Spacer for
basic setting of
pump stroke
FiguRe 4.9 alpha cylinder lubricator unit (man Diesel)
134 Fuels and Lubes: Chemistry and Treatment
The load- or kilowaat-dependent rate is applied rather than the revolutions per
minute- or mean effective pressure-dependent rate of other lubricator systems.
Two basic requirements have to be addressed: the cylinder oil dosage must
not be lower than the minimum needed for lubrication; and the additive amount
supplied through the BN (the alkalinity throughput) must be sufficient only for
neutralization and for keeping the piston ring pack clean. As the second cri-
terion usually overrides the first, the following determine the control: the cyl-
inder oil dosage shall be proportional to the engine load (i.e., the amount of
fuel entering the cylinders) and the sulphur percentage in the fuel. A minimum
cylinder oil dosage is set to address the other duties of the lubricant, such as
securing sufficient oil film detergency.
LubRiCanT TesTing
Lubricants are a valuable indicator of the overall functioning and wear of
machinery. Under normal engine operating conditions, the deterioration of a
lubricant takes place slowly, but severe conditions and engine malfunctions
promote faster degradation. Monitoring lubricants in service and analysing the
results determine not only their condition but also that of the engine and auxil-
iary machinery they serve. All the major marine lubricant suppliers offer used
lube oil testing services to customers, with results and advice transmitted by
FiguRe 4.10 arrangement of alpha electronic cylinder lubricant system (man
Diesel)
FE
BN
FE
FE
BN
S
Fuel
Lube
Alpha
lube
Fuel pump
Alpha
MCU
MPX
Process
computer
Scav. box drain oil
e-mail, fax or post to owner and ship from specialist laboratories. The range of
analyses undertaken on engine lubricant samples submitted typically embraces
checks on:
l Water content: even in small quantities, water is always undesirable in a
lubricant because it can act as a contaminant. A check on the water content
will indicate defects in the engine, purifier and other auxiliary machinery.
Where water is present, testing determines whether it is fresh or sea water.
l Insoluble products: lubricants in an engine are contaminated by a number
of insoluble products. Monitoring their presence provides a very good
indication of the engine’s operating condition or the effectiveness of the
purifier or filter; it also safeguards against breakdowns since a sudden
increase in the insoluble products present indicates a malfunction.
l Viscosity: a measure of the ability of a lubricant to flow, viscosity cannot
be used in isolation to assess a lubricant’s condition but it yields useful
information in conjunction with other determining factors, such as the
level of oxidation or contamination by fuel, water or other elements.
l Flash point: the temperature at which the application of a flame will
ignite the vapours produced by an oil sample under standard conditions.
Below a certain value there is a high risk of very serious incidents in
service, including crankcase explosion. The flash point must therefore
be monitored very carefully.
l Base number (BN) or alkalinity reserve: during the combustion proc-
ess the sulphur contained in the fuel can produce acidic products that
can damage the engine; this acid must be neutralized to avoid extensive
corrosive wear of the cylinder liner or piston rings. Neutralization is the
role of specific additives in the lubricants, the amount and type of which
are measured by the BN, which represents the alkalinity reserve. Close
monitoring of the BN in service is essential to ensure that the lubricant
still has sufficient alkalinity reserve to perform correctly.
l Wear metal elements: monitoring changes in metal elements (measured
in ppm) provides vital information on how patterns of wear develop
inside the machinery. Regular monitoring detects any sudden increase in
a wear element, such as iron or copper, which would indicate that exces-
sive wear was occurring.
The correct interpretation of results dictates analyses on a regular basis so
that curves can be plotted and extrapolated to indicate trends. Any measurement
that deviates significantly from the curves must be investigated further; adopting
a historical approach to analyses can minimize the risk of machinery malfunc-
tion and breakdown. When machinery manufacturers offer no specific recom-
mendations, Lub Marine suggests the following as average sampling periods:
main engine 3–6 months
Diesel genset 6–12 months
Lubricant testing 135
136 Fuels and Lubes: Chemistry and Treatment
hydraulic system 12 months
Turbocharger 6 months
gearing 12 months
air and gas compressors 12 months
miCRobiaL ConTaminaTion oF FueLs anD LubRiCanTs
Shipboard microbial fouling and corrosion have become more commonplace
and will probably continue to increase due to fuel oil formulation and handling
trends, polluted harbour waters and regulatory pressures.
Naval architects and shipbuilders are advised to design systems that are
less conducive to harbouring microorganisms and more readily sampled and
decontaminated if problems are experienced. Comprehensive onboard test kits
are available for detecting and quantifying microbial contamination and for
monitoring the success of anti-microbial measures.
Microbial contamination can manifest itself in the infection of fuel, lubri-
cants, cooling water and bilge and ballast waters. The results can be engine dam-
age (pistons and cylinder liners may wear faster, and filters and fuel-injection
nozzles become plugged, sometimes within a few hours); fuel tank pitting cor-
rosion and accelerated localized pitting; and general wastage corrosion of bilge
pipes, tank bottoms and hulls. In some cases, internal and external microbial
attack has led to rapid ship structural perforation. Of special concern is the pos-
sibility that certain strains of bacteria may endanger the health of the crew, as
would the incorrect handling and application of hazardous chemical biocides in
remedial treatment operations.
Various kinds of microbes are encountered: bacteria, moulds, and fungi
and yeasts. Bacteria are classified into two types: aerobic, which use oxygen to
oxidize their food, and anaerobic, which cannot tolerate oxygen. One anaero-
bic strain, termed sulphate-reducing bacteria (SRB), is particularly virulent and
produces corrosive sulphide.
Bacteria produce biosurfactants, which break down the oil/water interface,
promoting emulsions that are detectable when the fuel is tested for water sepa-
ration. If the infection is severe and longstanding, the aerobic bacteria consume
all the oxygen, and problems with SRB may result.
Microbes need water and a food source to survive, ingredients provided by
the hydrocarbons and chemical additives in oil. A temperature between 15°C
and 40°C is also required. Warm engine rooms offer an ideal breeding ground.
Laid-up tonnage or ships in intermittent service are most vulnerable to attack
because microbes dislike movement. Dormant fuel systems may be aggravated
by condensation and water leakage.
Various strategies are available for reducing the problems, but solutions
must be safe and environmentally acceptable. The details needed to build these
strategies into full working protocols will depend on individual circumstances,
the time available and access to anti microbial agents. There are many different
microbiological problems which need to be met with specific tailored solu-
tions but there are certain common principles of good practice which can be
implemented:
l Physical prevention: preventing ingress of inoculating microbes,
particularly those already adapted to growth in relevant environments.
Avoid spreading contamination from passing clean fluids through
contaminated pipes and filters and into dirty tanks. Minimize the
conditions which encourage microbial growth and water.
l Physical decontamination: settling, heat, filtration and centrifugal
procedures all aid decontamination, the choice of process depending
on equipment and time constraints.
l Chemical prevention: protecting against minor contamination, coupled
with good housekeeping to prevent rather than cure infection.
l Chemical decontamination: a wide range of chemical biocides is avail-
able. Only a few are appropriate to each specific application (there is
no universal eradication fluid). All are toxic and must only be used with
due regard to health and safety and environmental impact.
Microbial problems in the shipping industry were originally mainly con-
fined to distillate fuels and lubricants, but areas of attack have recently spread
to residual fuels and bilge, ballast and potable waters. Specialists cite the fol-
lowing contributory factors:
l Lower levels of shipboard manning and less experienced personnel have
undermined stringent housekeeping regimes.
l Adverse trading conditions have led to ships being laid up or deployed
intermittently, fostering long and undisturbed incubation periods for
opportunistic microorganisms.
l Marine pollution legislation under the Marpol 73/78 regulation which
restricts the pumping of bilges has led to water laying stagnant for
longer periods.
l Environmental restrictions on the use of toxic biocidal chemicals within
bilges and fuels exacerbate the problems associated with microbial
contamination.
l Lack of knowledge of the factors which cause microbial contamination
and accurate diagnosis of the operational problems being experienced.
l Shortcomings in the design of tanks, bilges and pipe systems whose con-
figuration should foster effective water draining and subsequent treatment.
There will always be an initial source of shipboard fuel contamination,
such as a shore tank, dirty pipeline, road tanker or polluted tank wash water.
Airborne contamination via tank breathers is less likely. Once infestation has
occurred, particular circumstances may encourage microbial proliferation
onboard. Further inoculation is then immaterial as the key aggravating factors
are water and warmth.
microbial contamination of fuels and lubricants 137