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Guidelines for Fuels and Lubes PurchasingOperation on Heavy Residual Fuels
3Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels
Contents
Fuel Oil Quality ................................................................................................ 5
Analysis Data ................................................................................................... 6
Fuel Oil Stability ............................................................................................... 8
Fuel Oil Treatment ............................................................................................ 8
Centrifuging Recommendations ........................................................................ 9
Fuel Sampling ................................................................................................ 11
Supplementary Fuel Oil Treatment .................................................................. 11
Fuel Oil System .............................................................................................. 13
Operational Aspects ....................................................................................... 14
Low-sulphur Fuel Operation ........................................................................... 15
Off-spec. Fuels............................................................................................... 15
Lube Oil Blending on Board ............................................................................ 17
Cylinder Oil, Low Speed Diesels ..................................................................... 18
Performance Verification of Cylinder Oils ......................................................... 19
Fuels and Lubes for Stationary Two-stroke MAN B&W Engines ...................... 19
List of References .......................................................................................... 20
5Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels
Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels MAN B&W Two-stroke Engines
Fuel Oil Quality
MAN Diesel’s engines are designed to
operate in accordance with the unifuel
principle. For specific guidelines for fuel
and lube oils for gensets, contact MAN
Diesel in Augsburg, Germany.
For guidance on purchase, reference
is made to ISO 8217, BS6843 and to
CIMAC recommendations regarding
requirements for heavy fuel for diesel
engines, edition 2003. According to
these, the maximum accepted grades
are RMH 55 and K55. The mentioned
ISO and BS standards supersede BS
MA 100, in which the limit is M9.
For reference purposes, an extract from
the relevant standards and specifica-
tions is shown in Table I.
Based on our general service experi-
ence, and as a supplement to the above-
mentioned standards, MAN Diesel issues
a guiding fuel oil specification, shown
in Table I.
Residual marine fuel standards
Category ISO-8217 (Class F)
Characteristic
Unit
Limit
RMA 30
RMB 30
RMD 80
RME 180
RMF 180
RMG 380
RMH 380
RMK 380
RMH 700
RMK 700
Test method reference
Density at 15 ºC
kg/m3
max.
960,0
975,0
980
991.0
991.0
1010.0
991.0
1010.0
ISO 3675 or ISO 12185 (see also 7.1)
Kinematic vis-cosity at 50 ºC
mm2/s a
max.
30,0
80.0
180.0
380.0
700.0
ISO 3104
Flash point
ºC
min.
60
60
60
60
60
ISO 2719 (see also 7.2)
Pour point (up-per) b - winter quality - summer quality
ºC
max. max.
0 6
24 24
30 30
30 30
30 30
30 30
ISO 3016 ISO 3016
Carbon residue %(m/m) max. 10 14 15 20 18 22 22 ISO 10370
Ash %(m/m) max. 0.10 0.10 0.10 0.15 0.15 0.15 ISO 6245
Water %(v/v) max. 0.5 0.5 0.5 0.5 0.5 ISO 3733
Sulphur c
%(m/m)
max.
3.50
4.00
4.50
4.50
4.50
ISO 8754 or ISO 14596 (see also 7.3)
Vanadium
mg/kg
max.
150
350
200
500
300
600
600
ISO 14597 or IP 501 or IP 470 (see also 7.8
Total sediment potential
%(m/m)
max.
0.10
0.10
0.10
0.10
0.10
ISO 10307-2 (see also 7.6)
Aluminium + Silicon
mg/kg
max.
80
80
80
80
80
ISO 10478 or IP 501 or IP 470 (see also 7.9)
Used lubricating oil (ULO) - Zinc - Phosphorus - Calcium
mg/kg
max. max. max.
The fuel shall be free of ULO d 15 15 30
IP 501 or IP 470 (see 7.7) IP 501 or IP 500 (see 7.7) IP 501 or IP 470 (see 7.7)
a Annex C gives a brief viscosity/temperature table for information purposes only. (1 mm2/s = 1 cSt)b Purchasers should ensure that this pour point is suitable for the equipment on board, especially if the vessel operates in both the northern and southern hemispheres.c A sulphur limit of 1.5 % (m/m) will apply in SOx emission control areas designated by the International Maritime Organization, when its relevant protocol comes into force. There may be local variations. d A fuel must be considered to be free of ULO if one or more of the elements zinc, phosphorus and calcium are below or at the specified limits. All three elements must exceed the same limits before a fuel shall be deemed to contain ULO.
Table I
6 Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels
In both tables the data refers to fuel
oils as delivered to the ship, i.e. before
onboard cleaning. Fuel oils within the
limits of this specification have, to the
extent of their commercial availability,
been used with satisfactory results in
MAN B&W two-stroke low speed diesel
engines.
It should be noted that current analysis
results do not fully suffice for estimating
the combustion properties of fuel oils.
This means that service results could
depend on oil properties which are not
known beforehand. This applies espe-
cially to the tendency of the fuel oil to
form deposits in combustion cham-
bers, gas passages and turbochargers.
As mentioned, the data refers to the fuel as
supplied, i.e. before the treatment.
If a fuel oil exceeding the data in Table I is
to be used, the engine builder or MAN
Diesel should be contacted for advice.
Analysis DataViscosity
Viscosity cannot be considered a qual-
ity criterion in its own right for fuel oils,
and is stated only for handling reasons
(pumps, preheaters and centrifuges).
Density
Density is related to the fuel quality be-
cause fuels derived from extensive re-
finery processing are left with a higher
carbon content, are more aromatic
and thus heavier. Therefore, fuels with
a high density are also high in carbon
residue and asphaltenes.
The water separation ability of the fuel
oil is ensured by limiting the density for
reasons of centrifuging, as stated in the
specification.
Density is normally measured at higher
temperatures, and the density at 15°C
is calculated on the basis of tables
which, depending on their origin, date
of issue, and the data on which they are
based, could give slightly differing den-
sities at 15°C.
Whereas the limit of 991 kg/m3 must
be observed when traditional centrifuges
(before 1985, purifier – clarifier) are used,
1010 kg/m3 is accepted provided that
modern centrifuges capable of hand-
ling fuels of such density are installed.
Flash point
The flash point limit is set as a safeguard
against fire only.
Pour point
The pour point indicates the minimum
temperature at which the fuel should
be stored and pumped. Temperatures
below the pour point results in wax for-
mation.
Sulphur
The corrosive effect of sulphuric acid
during combustion is counteracted by
adequate lube oils and temperature
control of the combustion chamber
walls.
The cylinder lube oil feed rate must be
according to the MAN Diesel recom-
mendation. The sulphur content has a
negligible effect on the combustion pro-
cess.
Carbon residue
The carbon residue is measured as
Conradson Carbon or Microcarbon.
Fuels with a high carbon residue con-
tent could cause increased fouling of
the gasways, necessitating more fre-
quent cleaning, especially of the turbo-
charger and exhaust gas boiler.
Some changes in combustion, requir-
ing adjustment of maximum pressures
for reasons of economy, could also be
attributed to a high carbon residue con-
tent. Part of the carbon residues repre-
sents asphaltenes.
The effect of asphaltenes on the com-
bustion process is similar to that of the
carbon residue. Asphaltenes also af-
fects the fuel oil lubrication properties.
Fuels with a high content of asphaltenes
may tend to emulsify with water.
Water
Water in the fuel should be removed by
centrifuging the fuel before use. This
applies especially to salt water, the
sodium content of which can result in
deposits on valves and turbochargers.
If the water cannot be removed online,
homogenising after centrifuging is recom-
mended.
Ash
Ash represents solid contaminants as
well as metals bound in the fuel (e.g.
vanadium and nickel). Part of the ash
could be catalyst particles from the refin-
ing process.
Catalyst particles are highly abrasive.
Solid ash should be removed to the
widest possible extent by centrifug-
ing, and cleaning can be improved by
installing a fine filter after the centrifuge
(e.g. 50 μm).
7Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels
Vanadium, magnesium and sodium
Vanadium is bound in chemical com-
plexes in the fuel and, consequently,
cannot be removed.
Vanadium deposits can be very hard,
and may cause extensive damage to
the turbocharger nozzle ring and tur-
bine wheel. The only way to remove
vanadium deposits is to disassemble the
components and erase the deposits me-
chanically.
Sodium is normally present in the fuel
as a salt water contamination and may,
as such, be removed by centrifuging.
Sodium can also reach the engine in
the form of airborne sea water mist.
Vanadium, in combination with sodium,
may lead to exhaust valve corrosion
and turbocharger deposits. This can
occur especially if the weight ratio of
sodium to vanadium exceeds 1:3, and
especially in the case of a high vana-
dium content.
MAN Diesel has limited data to show
that the level of sodium and vanadium
in combination, and in this ratio, has led
to the above-mentioned complications
on MAN B&W engines.
For lower contents of sodium and va-
nadium, the weight ratio is considered
of less importance (for a vanadium con-
tent less than 150 mg/kg).
Magnesium, either present in the fuel,
in salt water contamination or intro-
duced via additives can, to some ex-
tent, increase the melting point of the
vanadium, thus preventing the forma-
tion of deposits.
Aluminium and silicon
The limit to aluminium and silicon has
been introduced in order to restrict the
content of catalytic fines, mainly Al2O3
and SiO2, in the oil. 80 mg Al and Si
corresponds to up to 170 mg Al2O2 and
SiO2.
Catalytic fines give rise to abrasive
wear, and their content should, there-
fore, be reduced as much as possible
by centrifuging the fuel oil before it
reaches the engine.
MAN Diesel recommends that 80 ppm
of catalytic fines before the centrifuge
is reduced as much as possible by the
fuel centrifuge and, as a guideline, the
level should in any case not exceed 15
ppm after the centrifuge, see Ref. [1]
and Ref [2].
Ignition quality
Normally applied analytical data for fuel
oil contain no direct indication of igni-
tion quality, neither do current specifi-
cations and standards. However, this is
not an important parameter for engines
with high compression ratios.
In a few cases (less than five), we have
observed that the fuel had such poor
ignition quality that the engines could
not operate properly. Analysis of the
fuel in question revealed that these
fuels had all been contaminated by
chemical waste.
Tests performed together with fuel ana-
lysing institutes give indications of the
ignition and combustion qualities of the
different fuels. Test instruments utilising
a constant volume combustion technol-
ogy have been developed and are cur-
rently being used for marine fuel testing
at a number of fuel laboratories and build-
ers of marine diesel engines worldwide.
The test presents the Rate of Heat Re-
lease, reflecting the actual heat release
process and, thus, the combustion
quality of the fuel tested. By the use of
calibration fuels, a recorded ignition de-
lay in combination with the combustion
quality can be converted into an instru-
ment-related Cetane number.
The test results reflect the differences
in ignition and combustion properties of
diesel engine fuels resulting from varia-
tions in the chemical composition of the
fuels being tested.
However, these test results do not re-
flect the functions of the actual com-
bustion in the diesel engine, because
the tests are conducted at different
conditions/mechanisms than exist in
the engine.
With the modern high compression ra-
tio engines, the denoted differences in
the fuel, both good and bad, are not at
the level indicated by the test results.
The cetane number in an ignition qual-
ity test might, as such, only provide an
indication of the difference in the fuels,
but not whether this will have an influ-
ence on the engine performance.
8 Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels
Fuel Oil Stability
Fuel oils are produced on the basis of
widely varying crude oils and refinery
processes. Due to incompatibility, such
fuels can occasionally tend to be unsta-
ble when mixed, for which reason mix-
ing on board should be avoided to the
widest possible extent.
A mixture of incompatible fuels in the
tanks can result in rather large amounts
of sludge being taken out by the centri-
fuges or even lead to centrifuge blocking.
Inhomogeneity in the service tank can
be counteracted by recirculating the
contents of the tank through the cen-
trifuge. This will have to be carried out
at the expense of the benefits derived
from a low centrifuge flow rate as de-
scribed below.
With the introduction of new IMO emis-
sion regulations and the fuel sulphur
limit in SECAs (sulphur emission control
areas), more blending of fuels to com-
ply with the regulations is taking place.
For this reason, the risk of incompat-
ibility of fuels is also higher.
Fuel Oil Treatment
Fuels supplied to a ship must be treat-
ed on board before use. Detailed infor-
mation on fuel oil system layout can be
found in the CIMAC Recommendations
issued in 2005, Volume 9, concerning the
design of heavy fuel treatment plants for
diesel engines. Practically all fuel speci-
fications refer to fuel as supplied and,
as such, serve primarily as purchasing
specifications. Furthermore, the data in
a standard fuel analysis serves to adjust
the onboard treatment and is actually of
little use to the operator when referring
to the engine operational data.
Hence the basic design criterion is that
engines must be capable of accepting
all commercially available fuel oils, pro-
vided that they are adequately treated
on board.
For this purpose, a well-designed fuel
oil treatment system is a must. General
minimum recommendations for the lay-
out of such a system have been speci-
Fig. 1: Pressurised uni-fuel oil system for both main engine and gensets
Diesel oil
Heavy fuel oil
Heated pipe with insulation
- - - - - - - - - -
Automatic de-aerating valve
From centrifuges
Diesel oilservice
tank
Heavy fuel oilservice tank
Heater
Boosterpump
Supply pumps Circulatingpumps
Fuel oildrain tank
Main engine
Deck
Common fuel oil supply unit
To fresh water cooling pump suction
Full flow filterOverflow valve adjusted to 4 bar
Venting box
Auxiliary engines
Auxiliary engines
Auxiliary engines
9Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels
fied and should be complied with in
order to ensure proper treatment of the
fuel permitted by the guiding specifica-
tion. The operation of the fuel prepara-
tion system is the responsibility of the
operator. Good results require both the
correct system and the correct opera-
tion of the system.
The fuel oil system consists of a clean-
ing plant (comprising centrifuging) and
a pressurised fuel oil system.
Fig. 1 shows the pressurised fuel oil
system common for MAN B&W main
and GenSet engines.
Centrifuging Recommendations
Fuel oils, whether HFO or DO, should
always be considered as contaminated
upon delivery and should therefore be
thoroughly cleaned to remove solid as
well as liquid contaminants before use.
The solid contaminants in the fuel are
mainly rust, sand, dust and refinery cat-
alysts. Liquid contaminants are mainly
water, i.e. either fresh water or salt wa-
ter.
Impurities in the fuel can cause damage
to fuel pumps and fuel valves, and can
result in increased cylinder liner wear
and deterioration of the exhaust valve
seats. Also increased fouling of gas-
ways and turbocharger blades could
result from the use of inadequately
cleaned fuel oil.
Effective cleaning can only be ensured
by using a centrifuge. We recommend
that the capacity of the installed centri-
fuges should, at least, be according to
the centrifuge maker’s specifications.
To obtain optimum cleaning, it is of the
utmost importance that the centrifuge
is operated with as low a fuel oil viscos-
ity as possible, and that the fuel oil is al-
lowed to remain in the centrifuge bowl
for as long as possible.
Temperature of HFO before centrifuges
It is often seen that the HFO preheat-
ers are too small, or the steam supply
of the preheater is limited, or that they
have too low a set point in tempera-
ture. Often the heater surface is partly
clogged by deposits. These factors all
lead to reducing the separation tem-
perature and hence the efficiency of the
centrifuge.
In some cases, the temperature of the
HFO from the preheater is unstable and
fluctuates, which again results in im-
proper cleaning of the fuel.
In order to ensure that the centrifugal
forces separate the heavy contaminants in
the relatively limited time that they are
present in the centrifuge, the centrifuge
should always be operated with an inlet
temperature of 98°C.
A temperature decrease has to be fol-
lowed by a reduced throughput to en-
sure the same cleaning efficiency, see
Fig. 2.
The fuel is kept in the centrifuge as long
as possible by adjusting the flow rate
through the centrifuge so that it corre-
sponds to the amount of fuel required
by the engine without excessive recir-
culation. Consequently, the centrifuge
should operate for 24 hours a day ex-
cept during necessary cleaning.
Centrifuges with separate feed pumps
with a capacity matched to the engine
output are to be preferred.
Taking today’s fuel qualities into con-
sideration, the need for maintenance of
the centrifuges should not be underes-
timated.
100
90
80
70
77 90 92 94 96 98 100
Capacity for same separation (%)
cSt at 50 C
180 cSt300 cSt700 cSt
o
Fig. 2: Relationship of throughput and temperature
10 Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels
On centrifuges equipped with adjusting
screws and/or gravity disks, their cor-
rect choice and adjustment is of special
importance for the efficient removal of
water.
The centrifuge manual states which
disk or screw adjustment should be
chosen on the basis of the density of
the fuel.
The normal practice is to have at least
two centrifuges available for fuel clean-
ing purposes, operating in serial or par-
allel mode.
For old type centrifuges, results from
experimental work on the centrifuge
treatment of today’s residual fuel quali-
ties have shown that the best cleaning
effect, particularly in regard to removal
of catalytic fines, is achieved when the
centrifuges are operated in series, i.e.
in purifier/clarifier mode.
For the automatically operating centri-
fuges delivered from the mid-1980s,
suitable for treating fuels with densi-
ties higher than 991 kg/m3 at 15°C, it
is recommended to operate the centri-
fuges in parallel, as this results in reduced
throughput, i.e. longer retention time in the
centrifuge. However, the maker’s specific
instructions should be followed.
In this context, see section on high
density fuels. If the centrifuge capacity
installed is on the low side, in relation
to the specific viscosity of the fuel oil
used, and if more than one centrifuge is
available, parallel operation should be
considered as a means of obtaining an
even lower flow rate. However, in view
of the above results and recommenda-
tions, serious consideration should be
given to installing new equipment in
compliance with today’s fuel qualities
and flow recommendations.
For determination of the centrifuging
capacity, we generally advise that the
recommendations of the centrifuge
maker be followed, but the curves in
Fig. 3 can be used as a guide.
It is recommended that new centrifuges
have gone through a separation perfor-
mance standard test according to the in-
dustry standard CWA 15375.
In order to check the performance of
the centrifuge, fuel samples taken reg-
ularly before and after the centrifuge
should be analysed.
High Density Fuels
In view of the fact that some fuel oil
standards incorporate fuel grades with-
out a density limit, and also the fact
that the traditional limit of 991 kg/m3
at 15°C is occasionally exceeded on
actual deliveries, some improvements
in the centrifuging treatment have been
introduced to enable treatment of fuels
with higher density.
Since the density limit used so far is, as
informed by centrifuge makers, given
mainly to ensure interface control of the
purifier, new improved clarifiers, with
automatic desludging, have been in-
troduced, which means that the purifier
can be dispensed with.
With such equipment, adequate sepa-
ration of water and fuel can be carried
out in the centrifuge, for fuels up to a
density of 1010 kg/m3 at 15°C.
Therefore, this has been selected as
the density limit for new high density
fuel grades.
Thus we have no objections to the use of
such high density fuels in our engines,
provided that these types of centrifuges
are installed. They should be operated
in parallel or according to the centri-
fuge maker’s instructions.
Rate of flow, related to rated capacity of centrifuge80
60
40
20
200 400 600 1500 3500 7000 sec RI/100 Fo
%
Fig. 3: Centrifuge makers´ capacity specification
11Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels
Fuel SamplingSampling
To be able to check whether the speci-
fication indicated and/or the stipulated
delivery conditions have been complied
with, we recommend that a minimum
of one sample of each bunker fuel lot
be retained. In order to ensure that
the sample is representative for the oil
bunkered, the sample should be con-
tinuously taken at the ship manifold
throughout the bunkering period. This
is done by a continuous collection of
drip sample during the bunker delivery,
see Ref. [3].
This is without including the BDN (bun-
ker delivery note) for compliance with
IMO Annex VI.
Analysis of samples
The samples received from the bunker-
ing company are frequently not identi-
cal with the heavy fuel oil actually bun-
kered. It is also appropriate to verify the
heavy fuel oil properties stated in the
bunker documents, such as density,
viscosity and pour point. If these values
deviate from those of the heavy fuel oil
bunkered, there is a risk that the heavy
fuel oil separator and the preheating
temperature are not set correctly for the
given injection viscosity.
Sampling equipment
Several suppliers of sampling and fuel
test equipment are available on the
market, but for more detailed and ac-
curate analyses, a fuel analysing insti-
tute should be contacted.
Supplementary Fuel Oil Treatment
In a traditional system, the presence of
large amounts of water and sludge will
hamper the functioning of a clarifier, for
which reason a purifier has been used
as the first step in the cleaning process.
With the new automatic desludging
clarifiers, the purifier can, as mentioned,
be dispensed with. We consider the re-
moval of solids to be the main purpose
of fuel treatment.
Although not necessarily harmful in its
own right, the presence of an uncon-
trolled amount of water and sludge in
the fuel makes it difficult to remove the
solid particles by centrifuging.
Therefore, the following additional equip-
ment has been developed:
Homogenisers
Homogenisers are used to disperse
any sludge and water remaining in the
fuel after centrifuging. A homogeniser
placed after the centrifuge will render
fresh water (not removed by centrifug-
ing) harmless to the engine.
Homogenising may also be a means
to cope with the more and more fre-
quently occurring incompatibility prob-
lems, which are not really safeguarded
against in any fuel specification. Both
ultrasonic and mechanical homogenis-
ers are available.
Homogenisers can also be used for
moderate emission control in conjunc-
tion with emulsification of freshwater
into the fuel.
Homogenisers installed before the fuel
centrifuge can, when considering the
full range of the ISO 8217 fuel specifi-
cation, reduce the efficiency of the cen-
trifuge and, thus, the cleanliness of the
fuel delivered to the engine. The sodi-
um will not be removed from the fuel in
the form of salt water. The cat fines and
other abrasive material might be split
up into very small particles, which are
difficult for the centrifuge to separate
and which will still have a harmful wear
effect on the engine components.
Installation of homogenisers before the
centrifuge, see Fig. 4, is therefore not
advisable.
12 Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels
In order to reduce the NOx level in the
engine exhaust gas, water can be add-
ed to the fuel oil to create an emulsion.
Clean freshwater should be used, and
this is homogenised into the fuel oil at
a maximum ratio of approx. one part of
water to two parts of fuel oil. The water
emulsion can be stable with HFO but
with lighter fuels, such as gas oil and
diesel oil, it may be necessary to add
an emulsifier to the fuel oil before ho-
mogenising the fuel and water. The ho-
mogeniser is located between the HFO
service tank and the engine, i.e. after
the fuel oil purifiers.
Fine filters
Fine filters are placed directly after the
centrifuge, or in the supply line to the
engine, in order to remove any solid
particles not taken by centrifuging. The
mesh is very fine, i.e. down to 5 μm.
Homogenising before a fine filter can
reduce the risk of fine filter blocking by
the agglomeration of asphaltenes.
To F.W. coolingpump suction Full flow filter
Mainengine
Circulating pumps
Acceptable locationof homogeniser
Supply pumps
Heavy fuel oilservice tank
Dieseloil
servicetank From diesel centrifuges
Fuelstorage
tank
Suggested location of homogeniserby some suppliers.
Not acceptablefor engine performance
Deck
Automatic deaerating valve
Venting tank
Diesel oilHeavy fuel oilHeated pipe with insulation
To drain tank
F.O. draintank
TSA
304
PI PI
PSA307
TI TI
VSA303
Centrifuges
Preheater
TE 8005
PT 8002
VT 8004
Fig. 4: Pressurised fuel oil system, with homogeniser
13Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels
Fuel Oil System
A pressurised fuel oil system, as shown
in Fig. 1, is necessary when operating
on high viscosity fuels. When using high
viscosity fuels requiring high preheating
temperatures, the oil from the engine
fuel oil system to the return line will also
have a relatively high temperature.
The fuel oil pressure measured on the
engine (at fuel pump level) should be
about 8 bar, which is equivalent to a cir-
culating pump delivery pressure of up
to 10 bar. This maintains a pressure mar-
gin against gasification and cavitation in
the fuel system, even at 150°C preheat.
In order to ensure correct atomisation,
the fuel oil temperature must be ad-
justed according to the specific fuel oil
viscosity used.
An inadequate temperature can influ-
ence the combustion and could cause
increased wear on cylinder liners and
piston rings, as well as deterioration
of the exhaust valve seats. Too low a
heating temperature, i.e. too high vis-
cosity, could also result in a too high
injection pressure, leading to excessive
mechanical stresses in the fuel oil sys-
tem.
In most installations, heating is carried
out by means of steam, and the viscosity
is kept at the specified level by a viscosity
regulator controlling the steam supply.
Depending on the viscosity/tempera-
ture relationship of the fuel oil (the vis-
cosity index), an outlet temperature of
up to 150°C might be necessary, as in-
dicated on the guidance curves shown
in Fig. 5, which illustrate the expected
heating temperature as a function of the
specific fuel oil viscosity in cSt/50°C.
The recommended viscosity meter set-
ting is 10-15 cSt. However, service ex-
perience has shown that the viscosity
of the fuel before the fuel pump is not
a too critical parameter, for which rea-
son we allow a viscosity of up to 20 cSt
after the heater. In order to avoid too
rapid fouling of the heater, the temper-
ature should not exceed 150°C.
7 43
10 52
12 5915 69
20 87
30 125
cSt SecRW
Normal heating limit
Approximate pumping limit
10 15 25 35 45 55 cSt/100 Co
30 60 100 180 380 600 cSt/50 Co
200 400 800 1500 3500 6000 sec. RW/100 Fo
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
Temperature after heater
Co
Approximate viscosityafter heater
Viscosity of fuel
Fig. 5: Heating chart for heavy fuel oil
14 Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels
Operational Aspects
All low speed engines from and in-
cluding the K-GF types (from around
1973) are equipped with uncooled, all-
symmetrical lightweight fuel injection
valves.
These allow constant operation on
heavy fuel, due to the built-in possibility
of circulating heated heavy fuel through
the high-pressure fuel pipes, and fuel
valves during engine standstill.
In view of the emission regulations and
the increased use of low-sulphur fuels,
a special procedure is made to protect
the engine when changing between fu-
els (see the chapter: ‘‘Low-sulphur Fuel
Operation’’).
If a change to diesel oil is necessary as
a result of, for instance, the need for
a major repair of the fuel oil system, a
prolonged stop, or the use of very low-
sulphur fuels, as required by environ-
mental legislation, the heavy fuel in the
system can be changed with diesel oil
at any time, provided the change-over
procedure is followed, even when the
engine is not running. See also the en-
gine instruction book.
During engine standstill, the heated fuel
oil circulating through the fuel system
does not require the same low viscosity
as recommended for injection.
Thus, in order to save steam, the heat-
ing temperature may be lowered by
some 20°C, giving the circulating oil a
viscosity of up to 30 cSt.
The temperature should be raised to
the recommended service value, as il-
lustrated in Fig. 5, about 30 minutes
before starting-up is expected.
As previously mentioned, the heating
temperature must not exceed 150°C,
and during operation it is not necessary
to apply pipe heating by means of heat
tracing. When running on diesel oil, the
heat tracing system must not be used
at all.
However, it should be noted that the
pipe heating system on drain pipes
should remain in operation when run-
ning on heavy fuel.
Engine
Compatibilityof mixed fuels!
Tank systemconsiderations!
Fuel change-over unit
Viscosity!
OilBN10-40-70!
High S% Low S%
Fig. 6: Considerations to be made to before changing between high/low sulphur fuels
Fig. 7: Recommended cylinder oil feed rates depending on the fuel sulphur level
15Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels
Low-sulphur Fuel Operation
Today, there are ECAs (emission control
area, based on EU and IMO regulations)
in the Baltic Sea, the North Sea and the
English Channel. And more such areas
are expected to come. In the USA, the
EPA (Environmental Protection Agency)
is considering to designate Long Beach
an ECA very soon.
The sulphur content has an impact on
the sulphur acid emission to the air, sea
and land, as well as a major impact on
the particle level in the exhaust gas.
Even though MAN B&W two-stroke en-
gines are largely insensitive to the fuel
quality, changing between fuels with
different levels of viscosity is an impor-
tant consideration to make.
The cylinder lube oil base number must
be considered. Operating on normal
BN70 cylinder oil for too long when
burning low-sulphur fuel will prevent
controlled corrosion on the cylinder lin-
ers.
The mechanism is a creation of an ex-
cess of deposits originating from the
cylinder oil’s additives. Low-BN oil is
available from the major oil companies,
and recommendations on the use of
low and high-BN oils are also available.
The fuel change-over process must fol-
low the thermal expansion of both the
fuel pump plunger and the barrel, and
a procedure has been created to avoid
causing damage to the fuel pumps.
An automatic change-over unit will be
available in 2009.
In order to ensure the creation of a hy-
drodynamic oil film between the fuel
pump plunger and barrel, a viscosity of
2 cSt is required at the engine inlet. This
may be difficult to achieve for some DO
and GOs, and some operators may
have to introduce a cooler in the fuel oil
system to ensure a satisfactory viscos-
ity level.
The ignition quality of a fuel oil is not
an issue for MAN B&W two-stroke en-
gines. MAN Diesel has conducted a
number of research tests showing that
the MAN B&W two-stroke engine is in-
sensitive to the poor ignition combus-
tion quality fuels on the market today.
A separate booklet called ‘‘Low-sulphur
fuel operation’’ is available from MAN
Diesel, Ref. [4].
Off-spec. Fuels
Several selected off-spec. fuels (i.e.
beyond ISO 8217) have been tested
on MAN B&W’s two-stroke research
engine:
� Natural gas
� Bitumen
� Orimulsion
� Tallow
Our research facility in Copenhagen is
available for such testing. In the event
that off-spec. fuels are considered for
use on MAN B&W engines, it is recom-
mended that MAN Diesel is contacted
for further information regarding opera-
tional experience and any necessary
precautions.
Table II shows the guiding biofuel spec-
ification for MAN B&W two-stroke low
speed diesel engines.
MAN Diesel can be contacted for fur-
ther recommendations on the use of
biofuels.
Guiding Biofuel Specification for MAN B&W
Two-stroke Low Speed Diesel Engines 1)
Designation
Density at 15 oC kg/m3 1010
Kinematic viscosity at 10 oC 2) cSt 55
Flash point oC >60
Carbon residue % (m/m) 22
Ash % (m/m) 0.15
Water % (m/m) 1.0
Sulphur 3) % (m/m) 5.0
Vanadium ppm (m/m) 600
Aluminium + Silicon mg/kg 80
Sodium plus potassium ppm (m/m) 200
Calcium ppm (m/m) 200
Lead ppm (m/m) 10
TAN (Total Acid Number) mg KOH/g 4) <25
SAN (Strong Acid Number) mg KOH/g 0
1) Valid at inlet to centrifuge plant 2) Pre-heating down to 15 cSt at engine inlet flange is to be ensured 3) Lodene, phosphorus and sulphur content according to agreement with emission controls maker 4) Experience shows that a high Total Acid Number has influence on the time between overhaul of the engine fuel system and, therefore, need to be adjusted accordingly
Table II
16 Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels
Lubricating Oil Qualities
Low speed diesel rust and oxidation in-
hibited alkaline engine oils of the SAE
30 viscosity grade should be chosen
for circulating oil. The oils should have
adequate dispersancy/detergency to
keep the crankcase and the piston
cooling spaces free from deposits.
For engines with an integrated gear
driven Power Take Off (PTO), a mini-
mum FZG load level (Foursquare gear
oil test) of 8 should be observed. For
electronically controlled engines, a min-
imum FZG load level of 10 is required.
Contamination of system lube oil
Increase of BN (Base Number) and vis-
cosity of the system lube oil during op-
eration is unavoidable.
The piston rod stuffing box separates
the combustion and scavenge air
spaces from the crankcase. Therefore,
lube oil will not be severely contami-
nated with combustion products and
used cylinder lube oil. However, some
cylinder lube oil leaks through the stuff-
ing box, down into the system lube oil
sump. This is revealed by increasing
BN and viscosity levels of the system
lube oil.
Normally, the increase will stop after
some time and remain at a stable level
where topping up with new system lube
oil, to make up for normal consump-
tion, will balance the degree of contam-
ination of the system oil with cylinder
lube oil.
Water may also contaminate system oil.
Excess water levels may harm tin-alu-
minum bearings, for which reason MAN
Diesel recommends that the water level
does not exceed 0.2% (0.5% water al-
lowed for shorter periods of time), Ref.
[5].
In some cases, fuel has been seen
leaking through the fuel pump umbrel-
la sealings into the system oil. Fuel is
known to form deposits on hot spots,
i.e. in the piston undercrown space. It
is therefore important to keep the rec-
ommended overhaul intervals on fuel
pumps to secure that the pump pack-
ings/sealings are replaced.
BN level consideration
The increase in BN can influence the
ability of the oil to reject water by the
usual centrifuging. Water together with
calcium compounds from oil additives
may form calcium hydroxide recom-
mended to ensure calcium carbonate
and build up a deposit of lacquer on
the bearings. Another risk is the in-
creased sludge formation when water
is present.
Experience shows, however, that many
engines are operating with up to 30 BN
(starting from approx. 6 BN) without
any operational problems, and without
any changes in the lube oil performance
that give reason for renewing the oil.
Table III
International brands of lubricating oils which have been applied with satisfactory results on MAN B&W engines, on a
large number of vessels
Lubricating oils - Low speed main engines
Type Circulating oil Cylinder oil
Requirement SAE 30, BN 5-10 SAE 50, BN 60-80 SAE 50, BN 40-50
Oil company
BP Energol OE-HT 30 Energol CLO-50M/CL 605 Energol CL 505/CL-DX 405
Castrol CDX 30 Cyltech 70/80 AW Cyltech 40 SX/50 S
Chevron (Chevron, Texaco, Caltex)
Veritas 800 Marine 30
Taro Special HT 70
Taro Special HT LS 40
Total Atlanta Marine D 3005 Talusia HR 70/Talusia Universal Talusia LS 40
Exxon Mobil Mobilgard 300 Mobilgard 570 Mobilgard L540
Shell Melina 30/30S Alexia 50 Alexia LS
* depending on load profile and sulphur content, see MD recommendation for cylinder feed rate
17Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels
An increase in BN to an equilibrium
value of up to 25 in BN and in viscosity
from SAE 30 to SAE 40 is considered
normal, and no action is called for. An
increase beyond that is not really harm-
ful and can, in most cases, be counter-
acted by new low-BN topping oil.
The circulation oil consumption on the
MC/ME/ME-B/C/S engines is very low
because the engines are designed to
have fewer leaks and because of the
much reduced stuffing box oil drain,
compared to previous engine types,
causing a higher increase in BN and
viscosity. Therefore, it may be neces-
sary to add some new oil to the lube oil
sump at times to ensure a proper qual-
ity and BN level of the lube oil. This is
done by exchanging part of the circula-
tion oil in the sump based on an analysis
of the oil.
Lube Oil Blending on Board
A new blending-on-board (BoB) con-
cept makes it possible to add addi-
tives to the engine system oil and then
utilise it as cylinder lube oil. By top-
ping up the thereby used system oil,
a steady renewal of the oil is ensured
as well as improved viscosity control
and cleanliness. The oil suppliers get
the advantage of supplying only one oil
and a limited amount of additives. The
traditionally consumed cylinder oil is re-
placed with the blended lube oil.
Furthermore, the idea with the BoB
concept is that the operator will ulti-
mately be able to adjust the cylinder oil
BN to the current fuel sulphur level by
changing the blending ratio. In 2007,
MAN Diesel issued a No Objection Let-
ter (NOL) on a BN70 blend. The NOL
applies to a specific additive in a spe-
cific system oil.
Testing of a BN60 blend on is ongoing,
on an engine in service, and the condi-
tion is so far found to be satisfactory.
Technically, it is currently being investi-
gated how the blending-on-board con-
cept could cover all BN levels on just
the same additive package.
Some considerations must be made in
this respect:
� System oil condition prior to blending
must be acceptable
� Quality control of the additives must
be ensured
� Technical performance of additive
package in different concentrations
(BN40, BN50, BN60…) must be
clarified
MAN Diesel shares a common inter-
est with the oil companies – to keep
the lube oil expenses predictable and
optimal. Therefore, also in this field it
is of the utmost importance to ensure
the reliable performance of the blended
products. This requires continuous veri-
fication tests.
No-objection letters will be issued as
the tests with BoB and lower BN oils
are successfully concluded.
MAN Diesel can be contacted for infor-
mation on the test status.
18 Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels
Cylinder Oil, Low Speed Diesels
For engines operating on heavy residual
fuel oil, a cylinder oil with a viscosity of
SAE 50 and BN of 70 is recommended.
In most cases the high BN cylinder lubri-
cant will also be satisfactory during tempo-
rary operation on diesel oil/gas oil.
In general, changing the cylinder oil
type to correspond to the fuel type
used (i.e. bunker fuel or diesel oil/gas
oil) is considered relevant only in cases
where operation on the respective fuel
type is to exceed two weeks. However,
cylinder oil feed rate adjustments might
be required.
There is a high risk when using BN70
cylinder oils in connection with frequent
bunkering of low-sulphur fuels, with a
sulphur content of below to 1.5%, see
Ref. [6]
The main problem has been the ac-
cumulation of unused cylinder oil ad-
ditives, resulting in excessive deposits
on the piston topland. This has led to
high wear, and to a situation where in-
creased lubrication does not improve
the condition. On the contrary, in-
creased lubrication increases the for-
mation of deposits, leading to accelera-
tion of the problem.
It has been established that a certain
degree of controlled corrosion en-
hances lubrication, in that the corro-
sion generates small “pockets” in the
cylinder liner running face from which
hydrodynamic lubrication from the oil in
the pocket is created. The alternative,
no corrosion, could lead to bore polish
and, subsequently, hamper the crea-
tion of the necessary oil film on the liner
surface, resulting, eventually, in accel-
erated wear. Controlled corrosion – not
avoiding corrosion – is therefore crucial,
and adjusting the BN to the fuel oil sul-
phur content is essential.
Low alkaline cylinder lubricants are
therefore available on request from the
major lubricating oil suppliers.
Table III shows typical lube oils used
on marine applications together with
the fuel oils specified in Table I. In or-
der to control and prevent uncontrolled
sulphur corrosion, it has become the
industry standard for marine engines to
use cylinder lubricants with a BN of 70
in combination with the average marine
fuels, i.e. 380 cSt and 2.7% sulphur
content.
Special running conditions because of
frequent bunkering of low-sulphur fuels
and environmental fuel regulations (by
the authorities or self imposed), requir-
ing the use of low-sulphur fuel and spe-
cial running conditions, might call for
a lowering of the total alkaline additive
content. This can be done by lowering
the dosage towards our minimum feed
rate or, alternatively, by using one of the
specially designed cylinder oils with a
lower BN and with full detergency.
Service tests with such specially de-
signed low-BN oils have shown good
results. However, it may be difficult to
determine whether changing to a BN40
or BN50 cylinder oil will be adequate for
operation of ultra-low sulphur fuels. A
lower BN than 40-50 might be the fu-
ture oil for low-sulphur operation.
For this reason, we recommend that
you contact MAN Diesel, or the engine
builder, before operation on ultra-low
sulphur fuel.
General
It should be considered that, irrespective
of the sulphur content being high or low,
the fuels used in low speed engines are
usually low quality heavy fuels.
Table IV
Stationary applications
Ambient conditions Stationary engines Marine engines
Tropical Design
Maximum Average Minimum
Cooling water temp. yearly site yearly site yearly site 32°C 25°C
Air inlet temp. climatic cond. climatic cond. climatic cond. 45°C 25°C
Blower inlet pressure Depends on height above sea level 1000 mbar 1000 mbar
19Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels
Therefore, the cylinder oils must have
full capacity in respect of detergency
and dispersancy, irrespective of the BN
specified. This is a technology which
has to be mastered by the lube oil sup-
pliers, who can individually tailor a cylin-
der lube oil to the relevant fuel.
Breaking-in cylinder lube oils for testbed
running
In addition to determining the optimum
oil design for normal operation of the
two-stroke MAN B&W engines, we
also investigate and test various lube
oil designs in cooperation with the oil
companies to find the optimum cylinder
lube oils for testbed running.
Most builders of MAN B&W two-stroke
engines are using low-sulphur DO fuels,
primarily for environmental reasons.
This, in combination with a relatively
high running-in lube oil dosage, re-
quires a high detergency level in the
oil. Therefore, we generally recommend
the use of a BN70 cylinder oil, irrespec-
tive of the sulphur content of the fuel oil.
When introducing alucoating on piston
rings and semi-honed cylinder liners,
we also introduced a shorter running-
in period which, furthermore, limits the
period in which excess cylinder lube oil
is supplied, and improves the running-
in conditions. This means that the en-
tire running-in period, up to 100 hours,
is fully acceptable for using BN70 cylin-
der lube oils.
Performance Verification of Cylinder Oils
All oils listed have gone through a per-
formance test for about 4,000 running
hours on a relevant engine type in ser-
vice and have, during the test, been in-
spected by engineers from MAN Diesel,
in cooperation with the oil supplier.
When satisfactory results have been
achieved, MAN Diesel issues a ‘Let-
ter of No Objection’ for the use of the
oil on MAN B&W two-stroke engines.
However, MAN Diesel does not assume
responsibility for any damage caused
due to the quality of an oil mentioned in
a ‘Letter of No Objection’. The perfor-
mance of the oil is the responsibility of
the oil supplier. It is up to the operator
to obtain guarantees from the oil sup-
plier that the oil is suitable for operation
on the plant in question in conjunction
with the currently used fuel.
If an oil on the list fails to provide ac-
ceptable performance, then MAN
Diesel will work together with the oil
company to clarify the reasons and, if
needed, have a better oil introduced.
If an oil fails, the ‘Letter of No Objec-
tion’ will be withdrawn.
The list should not be considered com-
plete, and oils from other companies
may be equally suitable. Upon request,
MAN Diesel will inform whether a given
oil has been tested and whether the
test results were acceptable.
Further information about the oil test
and ‘Letter of No Objection’ can be
obtained by contacting MAN Diesel in
Copenhagen.
Fuels and Lubes for Stationary Two-stroke MAN B&W Engines
Stationary engines operate at load pat-
terns and ambient conditions which
differ widely from those of their marine
counterparts. This is illustrated in Fig. 8
and Table IV showing the typical oper-
ating conditions for both applications.
Thus, Fig. 8 shows that for stationary
engines, the average load is 95-100%
during 8,000 hours, or more, per year in
operation, whereas for marine engines
the average load is around 80% and,
furthermore, often only for 6,000 hours
per year in operation. This means that
stationary engines typically have a more
than 60% higher load factor than ma-
rine engines.
Stationary engines are exposed to
widely varying ambient conditions, i.e.
higher and lower air and cooling water
temperatures, see Table IV. Further-
more, stationary engines are frequently
exposed to fuel oils of non-marine qual-
ities. The fuel is often delivered from
one permanent supplier, meaning that
the quality from this supplier, good or
bad, will prevail.
Fig. 8: Typical load profile during a year in opera-tion
60
70
80
90
100
110
0 2,000 8,000hours
Time in service over one year
% load
Marine
Stationary
4,000 6,000
20 Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels
Therefore, lube oils, especially cylinder
oil, have to be individually selected and,
at times, even individually specified and
optimised in order to match the fuel oil
available.
Table III shows typical lube oils to be
used for marine applications together
with the fuel oils specified according to
ISO 8217. In order to control/prevent
sulphur corrosion, it has become the
industry standard for marine engines to
use cylinder lubricants with a BN of 70
for use with the average marine fuels.
This simple rule does not apply to sta-
tionary engines, where the sulphur level
in the fuel usually remains constant, i.e.
at the level set by the supplies avail-
able, or, when regulated by local leg-
islation, often shows a decreasing ten-
dency over the lifetime of the plant.
Hence, the constant use of a higher
than average sulphur content, possibly
even higher than that found in the ma-
rine specification, will call for the use of
a higher BN, and for this situation lube
oils with a BN of up to 100 are avail-
able.
Correspondingly, long-term use of
lower-than-average sulphur fuels will
call for the use of lower BN lube oils, as
described for low-sulphur marine fuels.
In addition, the engine load for station-
ary engines is usually very high, and the
ambient temperature is often higher as
well, ref. Fig. 8 and Table IV.
Hence, temperatures are high in the
combustion chamber, and the need to
counteract cold corrosion with alkaline
additives is lower, thus reducing the BN
requirement.
List of References
[1] “Heavy Fuel Oil Treatment”, Service
Letter SL05-452, Kjeld Aabo, MAN
Diesel, Copenhagen, Denmark
[2] “Marine diesel engines, catalytic
fines and a new standard to ensure
safe operation”, by Alfa Laval, BP
Marine and MAN B&W Diesel
[3] “Guidelines for the sampling of fuel
oil for determination of compliance
with Annex VI of MARPOL 73/78”,
Resolution by the IMO Marine En-
vironment Protection Committee,
MEPC 96
[4] “Operation on Low-sulphur Fuel”,
by Kjeld Aabo, MAN Diesel,
Copenhagen, Denmark, publica-
tion no.: 5510-0001-01ppr, Janu-
ary 2006
[5] “Cylinder Lubrication Guidelines
Operation on Fuels with Varying
Sulphur Contents All MC/MC-C
and ME/ME-C type engines Mk 6
and higher, with Alpha ACC Sys-
tem”, and “Cylinder Lubrication
New ACC Guidelines All MC/MC-C
and ME/ME-C type engines Mk
6 and higher, with Alpha ACC
System”, Service Letters SL05-
455 and SL07-479, Henrik Rol-
sted, MAN Diesel, Copenhagen,
Denmark
21Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels
MAN Diesel & TurboTeglholmsgade 412450 Copenhagen SV, DenmarkPhone +45 33 85 11 00Fax +45 33 85 10 30info-cph@mandieselturbo.comwww.marine.man.eu
MAN Diesel & Turbo – a member of the MAN Group
All data provided in this document is non-binding. This data serves informational purposes only and is especially not guaranteed in any way. Depending on the subsequent specific individual projects, the relevant data may be subject to changes and will be assessed and determined individually for each project. This will depend on the particular characteristics of each individual project, especially specific site and operational conditions. Copyright © MAN Diesel & Turbo. 5510-0041-02ppr Aug 2014 Printed in Denmark